3 Phase Short Circuit
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Short Circuit Analysis ProgramANSI/IEC/IEEE and Protective Device Evaluation User’s Guide Power Analytics Corporation 10805 Rancho Bernardo Road, Suite 270 San Diego, California 92127 U.S.A. U.S. Toll Free Phone: 800-362-0603 Fax: 858-675-9724 www.PowerAnalytics.com © Copyright 2012 All Rights Reserved Version 7.00.00 November 2012 Short Circuit Analysis Program ANSI/IEC/IEEE Table of Contents 1 UNIQUE FEATURES OF PALADIN DESIGNBASE SHORT CIRCUIT PROGRAM .......................................................... 1 1.1 2 INTRODUCTION .................................................................................................................................................. 3 2.1 2.2 2.3 3 W HAT’S NEW IN THIS RELEASE ......................................................................................................................... 2 TYPE OF FAULTS .............................................................................................................................................. 3 TERMINOLOGY .................................................................................................................................................. 4 SOURCES IN FAULT ANALYSIS ......................................................................................................................... 7 CONDUCTING A SHORT CIRCUIT STUDY IN DESIGNBASE ..................................................................................... 9 3.1 3.2 3.3 3.4 3.5 3.6 3.7 CALCULATION METHODS AND TOOLS .............................................................................................................. 9 SHORT CIRCUIT ANALYSIS OPTIONS: ............................................................................................................ 10 SLIDING FAULT: .............................................................................................................................................. 13 SERIES FAULT: ............................................................................................................................................... 17 AC ANSI/IEEE STANDARD ........................................................................................................................... 21 AC CLASSICAL SHORT CIRCUIT..................................................................................................................... 22 AC IEC 60909 SHORT CIRCUIT .................................................................................................................... 23 4 AC IEC 61363 SHORT CIRCUIT METHOD ............................................................................................................ 30 5 AC SINGLE PHASE SHORT CIRCUIT METHOD ..................................................................................................... 36 6 USING DESIGNBASE SHORT REPORT MANAGER ............................................................................................... 36 7 PROTECTIVE DEVICE EVALUATION (PDE) BASED ON ANSI/IEEE AND IEC-60909 ................................................ 41 8 SHORT CIRCUIT BACK ANNOTATION ................................................................................................................. 46 9 MANAGING SCHEDULES IN SHORT CIRCUIT CALCULATIONS ............................................................................. 47 10 NETWORK REDUCTION/EQUIVALENT ............................................................................................................... 54 10.1 10.2 10.3 10.4 11 APPENDIX I: SHORT CIRCUIT ANALYSIS INPUT DATA......................................................................................... 64 11.1 11.2 11.3 11.4 11.5 11.6 11.7 11.8 11.9 11.10 12 INTRODUCTION ............................................................................................................................................... 54 HOW TO PERFORM EQUIVALENT/REDUCTION CALCULATIONS ..................................................................... 54 SIMPLIFYING THE ORIGINAL SYSTEM BY USING THE COMPUTED EQUIVALENT ............................................ 58 VALIDATION AND VERIFICATION OF THE EQUIVALENT ................................................................................... 62 POWER GRID INPUT DATA ............................................................................................................................. 64 SYNCHRONOUS GENERATOR SHORT CIRCUIT INPUT DATA ......................................................................... 65 INDUCTION MOTOR SHORT CIRCUIT INPUT DATA ......................................................................................... 66 SYNCHRONOUS MOTOR SHORT CIRCUIT INPUT DATA.................................................................................. 67 HIGH VOLTAGE ANSI/IEEE CIRCUIT BREAKER SHORT CIRCUIT INPUT DATA ............................................ 68 LOW VOLTAGE ANSI/IEEE CIRCUIT BREAKER SHORT CIRCUIT INPUT DATA ............................................. 69 LOW VOLTAGE IEC CIRCUIT BREAKER SHORT CIRCUIT INPUT DATA .......................................................... 69 LOW VOLTAGE ANSI/IEEE FUSE SHORT CIRCUIT INPUT DATA .................................................................. 70 MEDIUM / LOW VOLTAGE IEC FUSE SHORT CIRCUIT INPUT DATA............................................................... 70 UPS ........................................................................................................................................................... 71 APPENDIX II: THEORETICAL BACKGROUND ....................................................................................................... 72 12.1 ANSI/IEEE STANDARD.................................................................................................................................. 72 i ................................................. 115 ii .......................................... 60 Figure 27: Equivalent Feeder between Buses BBB138 and GGG138 ... 19 Figure 7: IEC-61363 Short Circuit Chart ................................................................................................................................4 12........................... 45 Figure 13: Short Circuit Annotation Window ............................. 101 Figure 34: Percentage D................................................... 48 Figure 16: Motor Status inside a Schedule .................................................... 13 Figure 4: Report Manager for Sliding Fault Calculation .............................................................. Part 2 ........................................................................................................... 10 Figure 2: 3-Phase Annotation Results ............ 55 Figure 21: Selecting Network Equivalent Report Option .......................................................................... 100 Figure 33: Device Evaluation.......................................................................................................................................................................................................................... 59 Figure 26: Equivalent Generator at Bus ZZZ69 ..........................2 12..................................................... 63 Figure 32: Device Evaluation................................................................................ 114 Figure 37: IEC PDE Flow Chart – Part 3 .................. 14 Figure 5: Unbalanced system ...................... 74 ANSI/IEEE STANDARD BASED DEVICE EVALUATION (PDE IEEE) .............................................................................................................................................. 38 Figure 10: Short Circuit Professional Report ................................................ 49 Figure 17: Motor Loading / Usage inside a schedule ....................................... 92 IEC STANDARD BASED DEVICE EVALUATION (PDE IEC) ............................................................................................................................................................ 49 Figure 18: Short Circuit at MCC bus and branch contributions .............................................................................................................................................................................................................................................................................................. 17 Figure 6: Report Manager for Series Fault Calculation .................... 48 Figure 15: Feeder Representation inside a Schedule ...............5 IEC 60909 ..................................................................................................................................... 102 PROTECTIVE DEVICE EVALUATION BASED ON IEC STANDARD ........................ 62 Figure 31: Fault Currents the Reconstructed System ...................................3 12........................................................................................................................................................... 39 Figure 11: Protective Device Evaluation List .................................................. 113 Figure 36: IEC PDE Flow Chart – Part 2 ........................................................... .................................... ANSI Standard.................. 35 Figure 8: Short Circuit Report Manager ...........................................................Short Circuit Analysis Program ANSI/IEC/IEEE 12.......... 43 Figure 12: ANSI PDE Summary Report .......................................................... 59 Figure 25: Equivalent Generator at Bus GGG138 ................................... 51 Figure 19: Part of the System to be Reduced ......................... 12 Figure 3: Sliding Fault .................................................. 46 Figure 14: Motors inside schedule ................................................................................................................................................................................................................................. 58 Figure 24: Equivalent Generator at Bus BBB138 .................................................................... 61 Figure 29: Equivalent Transformer Between Buses BBB138 and ZZZ69 ............................................................................................................ 113 List of Figures Figure 1: Short Circuit Analysis Basic Option .................................................................................................................................................................................................... 56 Figure 22: Sample Network Equivalent Report ............................ 61 Figure 30: Fault Currents in Original Network ..................................................... 57 Figure 23: Reconstructed System Using the Calculated Equivalent ............................................................................................ ANSI Standard................................................................................................C......................................................................................................................................... for different time constant. Part 1 ............................................................................................................................................ 60 Figure 28: Equivalent Transformer between Buses GGG138 and ZZZ69 ................................................................................. current component in relation to the time interval from initiation of short-circuit current........ 36 Figure 9: Short Circuit Excel Report ..................................................................... 54 Figure 20: Selecting Buses for Network Equivalence ....................... 106 Figure 35: IEC PDE Flow Chart – Part 1 ................... ......................... 85 Table 5: IEC voltage factor............................................................................................................................... Please accept and respect the fact that Power Analytics Corporation has enabled you to make an authorized disk as a backup to prevent losing the contents that might occur to your original disk drive........................................................................pdf You will find the Test/Job files used in this tutorial in the following location: C:\DesignBase\Samples\3PhaseSC Test Files: ANSI-YY............................ lease.......... If you do not have or are unfamiliar with the contents of your EULA for this software........................ They are not substitutes for your professional judgment or for independent verification and testing of results as they pertain to your specific application........... REDUCTION_ORIGNAL... 104 Table 10: Icu and k factor............. rent or otherwise distribute Power Analytics Corporation programs / User's Guides to anyone without prior written permission from Power Analytics Corporation.............................................................................. 8 Table 3: IEC c factor ........................................................ The file name is: Short Circuit Analysis Program 3_Phase_Short_Circuit................................................................ You must comply with these terms and conditions in applying the instructional material in this manual. 108 Table 11: CB Name plate data ......................................... DO NOT sell........... 92 Table 7: K factor ............ 109 Note: You can view this manual on your CD as an Adobe Acrobat PDF file................. and understand a copy of your EULA before proceeding...... iii ................... IEC3632.......... 7 Table 2: 30 cycles calculation impedance ........................... read..... SC_MCC_SCHEDULE.. 86 Table 6: CB rated interrupting time in cycles .............................................................. REDUCTION_EQUIVALENT IMPORTANT NOTE: Power Analytics Corporation’s software products are tools intended to be used by trained professionals only............................ Use of all Power Analytics Corporation software products is governed by the terms and conditions of the EndUser License Agreement (“EULA”) you accepted when purchasing and installing the software............................................ 96 Table 9: n factor based on PF and short circuit level ...........Short Circuit Analysis Program ANSI/IEC/IEEE List of Tables Table 1: Recommended ANSI Source Impedance Multipliers for 1st Cycle and Interrupting Times .................................................................................................................................... give........................................................ 29 Table 4: Resistivity and equivalent earth penetration ........ All Rights Reserved............................ lend................ No part of this publication may be reproduced without prior written consent from Power Analytics Corporation............................................................ T123.... you should request.............. 95 Table 8: Default Device X/R Values Using DesignBase’s Library .................... . 000 buses Modeling Exact short circuit current and contributions computation using Three-Sequence Simulate sliding and open conductor faults High speed simulation by utilizing state-of-the-art techniques in matrix operations (sparse matrix and vector methods) Automated reactor sizing for 3 Phase networks Exporting and importing data from and to Excel Import system data from Siemens/PTI format into Paladin DesignBase Customize reports Professional report tool based on Crystal Reports UPS source bypass Support of ANSI and IEC standards for PDC (protective device coordination) Support of ANSI and IEC standards for PDE (protective device evaluation) Fully integrated with ARC flash program Fully integrated with PDC Minimum and maximum utility fault contribution UPS bypass mode and motors fed from VFD features 1 .Short Circuit Analysis Program ANSI/IEC/IEEE 1 Unique Features of Paladin DesignBase Short Circuit Program The salient features of the Paladin DesignBase advanced short circuit program: Fault analysis of complex power systems having over 50. Short Circuit Analysis Program ANSI/IEC/IEEE 1.1 What’s new in this release New Bus Short Circuit Evaluation feature (PDE). Additional flexible annotations. Augments IEC-61363 motor short circuit model with a new user defined percent rating of let-through current. transformers and feeders. New Case Study feature that enables to save customized short circuit options. Introduces advanced inverter options for accurate calculations. 2 . Improved photovoltaic short circuit model. Enables easy setup of multiple maximum and minimum fault calculations. and LLG faults. Extended computation of thermal currents to LG. LL. Provides options to simultaneously display several short circuit components on the one line diagram. New Impedance Tolerance feature for generators. New VFD Regenerative Mode. Seamlessly provides instant comparison of short circuit results and bus ratings. the total energy is less than a three-phase fault. Such cases include faults that are close to the following types of equipment: The Wye side of a solidly grounded delta-wy transformer / auto-transformer The Wye-Wye solidly grounded side of a three winding transformer with a delta tertiary winding A synchronous generator solidly connected to ground The Wye side of several Wye grounded transformers running in parallel 3 . 2. Protective devices such as circuit breakers and fuses are applied to isolate faults and to minimize damage and disruption to plant’s operation. There are cases that can lead to single phase fault currents exceeding the three-phase fault currents.1 Type of Faults The most common faults are: Three-Phase Fault. with or without ground (3P.Short Circuit Analysis Program ANSI/IEC/IEEE 2 INTRODUCTION A short circuit is an accidental electrical contact between two or more conductors. however. or 3P-G) Single line to ground Fault (L-G) Line to Line Fault (L-L) Line to line to ground Fault (L-L-G) Estimated frequency of occurrence of different kinds of fault in power system is: 3P or 3P-G: L-L: L-L-G: L-G: 8% 12 % 10 % 70 % Severity of fault: Normally three-phase symmetrical short circuit (3P) can be regarded as the most severe condition. the current in a pole of a switching device at the instant of arc initiation (pole separation). 4 . Fault – an abnormal connection.the maximum rms value of calculated short circuit current for medium and highvoltage circuit breakers. Breaking Current .2 Terminology Arcing Time . It is the sum of the relay or release delay and opening time.6 factor to the first cycle symmetrical AC rms short circuit current. Contact Parting Time . with any applicable multipliers with regard to fault current X/R ratio.6 times the circuit breaker rated maximum symmetrical AC rms interrupting current. between two points of different voltage potentials.the maximum short circuit current that the power system could deliver at a given circuit point assuming negligible short circuit fault impedance.the interval of time between the instant of the first initiation of the arc in the protective device and the instant of final arc extinction in all phases. b):L-L. and immediately thereafter latch closed.the maximum asymmetrical current capability of a medium or high-voltage circuit breaker to close. for normal frequency making current. line-to-line-to-ground. The close and latch asymmetrical rms current capability is 1. line-to-ground 2. and d): L-G. including the arc. c):L-L-G. of relative low impedance. It is also known as “Interrupting Current” in ANSI Standards.” The rms asymmetrical rating was formerly called momentary rating. whether made accidentally or intentionally. Often. Close and latch duty is also called “first cycle duty. during the first cycle. the close and latching duty calculation is simplified by applying a 1. Crest Current / Peak Current – the highest instantaneous current during a period. line-to-line. Close and Latch Duty .the interval between the beginning of a specified over current and the instant when the primary arcing contacts have just begun to part in all poles.Short Circuit Analysis Program ANSI/IEC/IEEE Type of Short Circuits: a):3P – three-phase. Available Short Circuit Current . Close and Latch Capability .” and was formerly called momentary duty. Often called “first cycle capability. Initial short circuit current IK" is the rms value of the symmetrical short circuit current at the instant of occurrence of the short circuit. Making Current – the current in a pole of a switching device at the instant the device closes and latches into a fault. Momentary Current Rating – the maximum available first cycle rms asymmetrical current which the device or assembly is required to withstand. Sometimes referred to as “Breaking Current”. Depending on the Standard.circuit power S K " is the product of System breaking power S B is the product of 3 *I a * UN 5 3 *I K "*UN . Rated voltage VR the phase-to-phase voltage. Short circuit current is the current that flows at the short circuit location during the short circuit period time. is the rms value of the symmetrical short circuit current flowing through the switching device at the instant of the first contact separation. IEC U R the rated voltage is the maximum phase-to-phase voltage. Interrupting Current – the current in a pole of a switching device at the instant of arc initiation. according to which the power system is designated. Branch short circuit currents are the parts of the short circuit current in the various branches of the power network. First Cycle Rating – the maximum specified rms asymmetrical or symmetrical peak current capability of a piece of equipment during the first cycle of a fault. Initial symmetrical short . Maximum asymmetrical short circuit current Is is the highest instantaneous rms value of the short circuit current following the occurrence of the short circuit. on the opening of a mechanical switching device under short circuit conditions. Peak Current – the maximum possible instantaneous value of a short circuit current during a period. I b . Offset Current . Symmetrical breaking current Ia . First Cycle Duty – the maximum value of calculated peak or rms asymmetrical current or symmetrical short circuit current for the first cycle with any applicable multipliers for fault current X/R ratio. IEC 60909. IEC60909. Symmetrical short circuit current is the power frequency component of the short circuit current. Nominal Voltage UN – (IEC) the nominal operating voltage of the bus. It was used on medium and high-voltage circuit breakers manufactured before 1965.Short Circuit Analysis Program ANSI/IEC/IEEE Fault Point X/R – the calculated fault point reactance to resistance ratio (X/R). different calculation procedures are used to determine this ratio.an AC current waveform whose baseline is offset from the AC symmetrical current zero axis. present terminology: “Close and Latch Capability”. Short-circuit currents in three-phase AC systems. 399 – 1997. IEEE Recommended Practice for Power Systems Analysis (IEEE Brown Book) ANSI/IEEE Standard C37. Low-voltage switchgear and controlgear – Part 3: Switches. Standard for Safety for Molded-Case Circuit Breaker. Short Circuit Current Calculation in ThreePhase Ac Systems UL 489_9 – 1996. Molded-Case Switches. switchdisconnectors and fuse-combination units BS EN 62271-100:2001. Direct earthing / effective earthing is the direct earthing of the neutral points of the power transformers.010 – 1979. Low-voltage switchgear and controlgear – Part 2: Circuit breakers EN 60947-3:1999. Low-voltage switchgear and controlgear – Part 1: General rules IEC 60947-2:2003. IEEE Recommended Practice for Electric Power Distribution of Industrial Plants (IEEE Red Book) ANSI/IEEE Std. Short-circuit currents in three-phase AC systems. IEEE Application Guide for AC High-Voltage Circuit Breakers Rated on a Total Current Basis ANSI/IEEE Standard C37. Short circuit earth current is the short circuit current.5-1979. that flows back to the system through the earth. High-voltage switchgear and controlgear – Part 100: High-voltage alternatingcurrent circuit-breakers IEC 62271-111:2005-11. Pierre IEC 60909-0/2001-07. IEEE Application Guide for AC High-Voltage Circuit Breakers Rated on a Symmetrical Current Basis ANSI/IEEE Standard C37. Part 3: Currents during two separate simultaneous line-to-earth short-circuits and partial short-circuit currents flowing through earth IEC 60947-1:2000-10. dry vault and submersible automatic circuit reclosers and fault interrupters for alternating current systems up to 38 kV 6 . by Conrad St. or part of it. pad-mounted. Dynamic stress is the effect of electromechanical forces during the short circuit conditions. Equivalent generator is a generator that can be considered as equivalent to a number of generators feeding into a given system. disconnectors. Part 0: Calculation of currents IEC 60909-3/2003. and Circuit-Breaker Enclosures “A Practical Guide to Short-Circuit Calculations”. IEEE Standard for Low-Voltage AC Power Circuit Breakers Used in Enclosures IEC-909 – 1988. International Electro technical Commission.Short Circuit Analysis Program ANSI/IEC/IEEE Minimum time delay t min is the shortest possible time interval between the occurrence of the short circuit and the first contact separation of one pole of the switching device. DesignBase Short Circuit Analysis Program is based on ANSI/IEEE and IEC Standards and fully complies with the latest ANSI/IEEE/IEC Standards: ANSI/IEEE Std.13-1990. Thermal stress is the effect of electrical heating during the short circuit conditions. 141 – 1993. High-voltage switchgear and controlgear – Part 111: Overhead. 13 . The following table shows the type of device and its associated duties using the ½ cycle network.5* Z Medium Induction Motors 50 to 249 HP or 250 to 1000 HP <2poles 1.010 ANSI C37.010 " 1.010 " ANSI C37.67* Z " 3* Z ∞ " 7 " ANSI C37. The ½ cycle network is also referred to as the sub transient network.010 " dv ANSI C37.Short Circuit Analysis Program ANSI/IEC/IEEE 2. low voltage molded-case breakers.3 Sources in Fault Analysis Power utilities. and regenerative drives are sources in fault calculations.5* Z dv ANSI C37.010 1. because all rotating machines are represented by their sub transient reactance. high and low voltage fuses and withstand currents for switches and highvoltage breakers. ½ Cycle Network Duty The decay of short circuit current is due to the decay of stored magnetic energy in the equipment. all rotating electric machinery.2* Z Small Induction Motors <50 HP 1. Type of Device Duty High voltage circuit breaker Low voltage circuit breaker Fuse Switchgear and MCC Relay Closing and latching capability Interrupting capability Bus bracing Instantaneous settings Table 1: Recommended ANSI Source Impedance Multipliers for 1st Cycle and Interrupting Times Source Type 1/2-Cycle Calculations Interrupting Time calculations Reference (1.5 to 4 cycles cpt) Remote Utility (equivalent) Z " s Local Generator Z Synchronous Motor " Z dv Large Induction Motors: >1000 HP or 250 HP and 2 poles Zs " dv Z Z" ANSI C37. ½ cycle short circuit currents are used to evaluate the interrupting duties for low-voltage power breakers. The impedance used during the first ½ cycle is the sub-transient impedance. It is generally used for the first ½ cycles up to a few cycles. The type of power system components and their representations in 30-cycle networks are shown in the following table. Table 2: 30 cycles calculation impedance Source Type 30 Cycle Calculation Impedance Power Utility /Grid Z s" Generators ' Z dv Induction Motors Synchronous Motors Infinite impedance Xd 8 . synchronous motors.5 – 4) cycles after the fault. Type of Device Duty High voltage circuit breaker (>1.Short Circuit Analysis Program ANSI/IEC/IEEE Harmonic Filters Z% 100 Tuned _ harmonic X”d = / 1 LRC For Induction Motors 1.5-4 Cycle Network This network is used to calculate the interrupting short circuit current and protective device duties (1. Note that induction machines. and condensers are not considered in 30-cycle fault calculation.0 kV) Unfused Low Voltage PCB without instantaneous All Other Low voltage circuit breaker Fuse Switchgear and MCC bus Interrupting capability Interrupting capability N/A N/A N/A Steady State or 30-Cycle Network This network is used to calculate the steady state short circuit current and duties for some of the protective devices 30 cycles after the fault occurs (delayed protective devices). The following short circuit calculation methods are available: AC ANSI/IEEE (separate R and X. Open the “T123” sample file under the C:\DesignBase\Samples folder and click on the short circuit icon as shown below: The short circuit toolbar will appear showing the analysis method pick list and their corresponding tools Paladin DesignBase provides several short circuit calculation methods based on ANSI/IEEE Standards and IEC Standards for both AC three-phase and single-phase networks. (Academic Z complex method.Short Circuit Analysis Program ANSI/IEC/IEEE 3 CONDUCTING A SHORT CIRCUIT STUDY IN DESIGNBASE 3. as per ANSI/IEEE Standard) AC Classical. X/R from the complex Z) AC IEC 60909 AC IEC 61363 AC 1 Phase DC Classical DC IEC 61660 Their associated tools are listed below: Options Report Manager Back Annotation Analyze Reactor Sizing 9 .1 Calculation Methods and Tools To start DesignBase Short Circuit program. load flow calculated bus voltage or actual/name plate voltage Default output: Annotation or report 10 . AC IEC 60909.2 Short Circuit Analysis Options: While the “T123” sample file is open in DesignBase. Tolerance Tab: this tab enables to specify equipment impedance tolerances The Calculation Tab allows selecting the followings: Case Study: enables users to save combination of customized short circuit options Base voltage: o Adjusted by tap/turn ratio if power transformer is run on “off nominal” taps o System voltage Prefault voltage represents the bus voltage at the instant the fault is applied at that bus. faults can be performed only at all buses in this release. Click on the “Options” icon and the window below will appear.Short Circuit Analysis Program ANSI/IEC/IEEE 3. AC IEC 61363 and AC Single Phase calculation. Control Tab: this tab depends on the short circuit method that user selects. It can be: system voltage. AC Classical. AC Single Phase. Figure 1: Short Circuit Analysis Basic Option The Options window has three tabs: Calculation Tab: This tab has the same fields for AC ANSI/IEEE. line-to-line. and line-to-line-to-ground fault at all buses which are faulted for short circuit studies. line-to-line. by a simple click on the desired bus symbol. and lineto-line-to-ground fault at each selected bus which is faulted for short circuit studies. The highlighted bus/buses will be transferred to the “All Buses” List. line-to-ground. Select Base Voltage: System Voltage Select Prefault Voltage: System Voltage Contribution Level from fault location: 3 Default Output: Annotation Bus Type to select: All Buses 11 . while the “shift key” is being held down. or By highlighting the bus name in the Short Circuit Option window and then clicking on the “Add” button. This option is applied if the fault is calculated at one bus only Fault location: selected buses. select each bus individually Menu Driven: highlight the desired bus ID in the Short Circuit Option and then click on “Add”. If one Bus is selected. Notes: Faults at more than one bus. To remove a bus from the “Selected Buses” list highlight the bus name and click on the “Remove” button. then hold down the “shift key”. To remove a bus or several buses from the “Selected Buses” List. Selecting All Buses: Fault at all buses can be simulated by selecting the “All Buses” option under the “Short Circuit Analysis Basic Option”. not simultaneously. not simultaneously. line-to-ground. the program will place a three-phase. All faulted buses are colored in “Red”. are faulted individually in turn. sliding fault or series fault. the selected bus will be transferred to the “Selected Buses” list. the selected buses will be transferred to the “Selected Buses” list. (Sliding and series fault does not apply to IEC61363 or AC Single phase calculation) Miscellaneous options: use only X to calculate the faults Duty type for PDE based on: maximum branch fault flow or total bus fault current Fault Location Selection of One Bus: A Bus can be selected: Graphically on the one line diagram. are faulted individually. the short circuit program can determine the bus post-fault voltage and branch contributions up to 50 levels away of that fault. Selecting More Than One Bus: Graphically on the drawing space: click onto the desired first bus. all buses. Faults at “All Buses”. highlight the bus ID and click on the Remove button. On the drawing are displayed short circuit components and units as per user selection in the Short Circuit Back Annotation window.Short Circuit Analysis Program ANSI/IEC/IEEE Contribution level: Branch contribution levels away from the fault location to be shown in results. the program will place a three-phase. For this tutorial select in the Options window the following options: Default Output: Annotation. The calculated results are displayed either on the one-line diagram (if Default Output: Annotation is selected by the user) or printed in the output report (if Default Output: Report is selected by the user) Fault impedance. Depending on the specified fault type. Depending on the specified fault type. Figure 2: 3-Phase Annotation Results 12 . The following results will be displayed on the drawing.Short Circuit Analysis Program ANSI/IEC/IEEE Fault location: 18 Then click on the analyze icon. Short Circuit Analysis Program ANSI/IEC/IEEE 3. Figure 3: Sliding Fault 13 . The figure below shows examples of evenly spaced sliding faults (F1. “To” Bus “From” Bus F1 Click on the “Options” icon F F2 F3 F4 to select “Sliding Fault” as shown below. F3.3 Sliding Fault: Paladin DesignBase Short Circuit Program can simulate a fault along a feeder/cable/transmission line. and F4) and single point sliding fault at a specific location (F). F2. Using this option eliminates the need to create a dummy bus at a location along the feeder. To remove a Feeder/Cable from the “Selected Feeders and Cables” box. only one Feeder/Cable can be selected for Sliding fault calculation at a time. highlight the Feeder/Cable and click on the “Remove” button. In the latter option.Short Circuit Analysis Program ANSI/IEC/IEEE Selecting a Feeder / Branch: Highlight the desired Feeder/Cable in the “All Feeders and Cables” Box and then click on the Add button. In this release. Select feeder “3C – 12”. and then press on the “OK” button. Contributions from both ends of the feeder/line for each fault location as well as the voltages at the faulted location and at both ends are also reported: Fault type: 3-Phase Fault 14 . the program automatically divides the feeder/line into equidistant segments and fault currents are calculated for each intermediate point. The Report Manager for Sliding Fault Calculation will appear as shown below: Figure 4: Report Manager for Sliding Fault Calculation The program allows users to specify the Fault location on the selected Feeder at “Any Position” away from the “From Bus” or at a “Number of Fault Spots” evenly spaced alongside the selected feeder. The highlighted Feeder/Cable will be transferred to the “All Feeders / and Cables Box / List. the selected Feeder/Cable will be transferred to the “Selected Feeders and Cables” Box. Short Circuit Analysis Program ANSI/IEC/IEEE Units: Note: Line-to-line fault Line-to-ground fault Double-Line-to-Ground fault For fault Current: A or kA, with user defined decimal places For Capacity: kVA or MVA, with user defined decimal places For Bus Voltages: V or kV, with user-defined decimal places Per Unit MF, %X/R: with user-defined decimal places Sliding fault does not apply to IEC61363 and AC Single Phase calculation. For this tutorial, select branch contribution, then the “Any Position” option. Enter 150 feet in the “Away From Bus” field and click “OK”. The following report will be generated after clicking on the “Analyze” icon on the Short Circuit toolbar. Paladin DesignBase 3-Phase Short Circuit v7.00.00 Project No. : Page : 1 Project Name: Date : 10/23/2012 Title : Time : 02:53:14 pm Drawing No. : Company : Revision No.: Engineer: Jobfile Name: T123 Check by: Scenario : 1 : mode1 Case : 1 : Base -------------------------------------------------------------------------------Electrical One-Line 3-Phase Network for ANSI PDE -------------------Calculation Options -------------------Calculating Single Bus Fault with Fault Z = 0.00000 + j 0.00000 Ohms Fault Phases: Phase A for Line-Ground Fault Phase B,C for Line-Line or Line-Line-Ground Fault ANSI/IEEE Calculation: Using ANSI Std. C37.010-1979 or above. Separate R and X for X/R, Complex Z for Fault Current The Multiplying Factors to calculate Asym and Peak are Based on Actual X/R Peak Time Applies ATPC Equation Transformer Phase Shift is considered. Generator and Motor X/R is constant. Base Voltages : Use System Voltages Prefault Voltages : Use System Voltages 15 Short Circuit Analysis Program ANSI/IEC/IEEE Jobfile Name: T123 Page : 2 ------------------------------------------------------------Fault Spot Report for Sliding Fault Bus Results: 0.5 Cycle--Symmetrical--3P/LL/LG/LLG Faults ------------------------------------------------------------Fault Feeder From Bus To Bus Fault Spot : : : : 3C 3C 12 150 ->12 Fault R(Ohms) : Fault X(Ohms) : Length(Feet) : 0 0 300 Feet away from 'From Bus' Thevenin Imped. ANSI Pre-Flt 3P Flt. LL Flt. LG Flt. LLG Flt --------------- -----Bus Name kV kA kA kA kA Z+(pu) Zo(pu) 3P X/R ------------------------ ------- ------- ------- ------- ------- ------- ------- -------Fault Spot--0.48 31.17 27.00 28.73 31.31 3.8584 4.8751 10.678 Jobfile Name: T123 Page : 3 ---------------------------------------------------3.4------------Branch Report for Sliding Fault Branch Results: 0.5 Cycle--Symmetrical--3P/LG Faults ---------------------------------------------------------------Fault Feeder From Bus To Bus Fault Spot : : : : System Volt: 0.48 Fault Type Spot RMS( kA Spot X/R 3C 3C 12 150 : ): : ->12 Fault R(Ohms) : Fault X(Ohms) : Length(Feet) : 0 0 300 Prefault Volt: 0.48 Feet away from 'From Bus' kV 3-phase 31.17 10.68 Base Volt: L-L 27.00 0.48 L-G 28.73 kV kV L-L-G 31.31 * Stands for Secondary or Tertiary Side of Transformer or To Bus --> Fault Spot for Sliding Fault Feeder. 3-Phase Fault Line-Ground Fault Thevenin --------------- ------------------------------- --------------From Bus (kA) From Bus (kA) Impedance Branch Name %V Ia %Va %Vb Ia 3Io Z+(pu) Zo(pu) ------------------------ ------- ------- ------- ------- ------- ------- ------- ------0001 29.9 0.00 39.6 98.0 0.00 0.00 2.9575 2.5520 0002 29.9 0.00 39.6 98.0 0.00 0.00 2.9575 2.5520 0003 29.9 29.19 39.6 98.0 26.95 27.05 2.9575 2.5520 0004 29.9 -1.41 39.6 98.0 -0.87 -0.00 2.9575 2.5520 0005 29.9 0.00 39.6 98.0 0.00 0.00 2.9575 2.5520 0006 29.9 0.00 39.6 98.0 0.00 0.00 2.9575 2.5520 0007 29.9 0.00 39.6 98.0 0.00 0.00 2.9575 2.5520 16 Short Circuit Analysis Program ANSI/IEC/IEEE 3.4 Series Fault: Series fault types (one phase open, two phases open, and unequal series impedances) with or without neutral unbalance are supported in the Paladin DesignBase short circuit program. The series fault types are shown in the figure below. It should be noted that series faults are meaningful only if pre-fault loads have been taken into account (i.e. load flow solution is considered). For series faults, the equivalent voltage at the opening point is computed from the pre-fault system current at the unbalance point. The default fault impedances Za, Zb, and Zn are: Figure 5: Unbalanced system 17 Click “Ok” and the “Report Manager for Series Fault Calculation” will appear. B. the series fault feature is only supported by the “AC Classical” short circuit analysis method. 18 .0 In the current version of the program. open the Short Circuit Analysis Options and select “LF Voltage” under the Prefault voltage menu and the “Series Fault” field to perform open phase study on branch “3C->12”. using the same short circuit sample file “T123” as in previous sections.0 For two open phases (phases B and C) Default values: Za=Zn=0. select “AC Classical” under the “Analysis” short circuit toolbar menu. and C) Default values: Za=Zb=Zn=0. Then.Short Circuit Analysis Program ANSI/IEC/IEEE For one open phase (phase A).0 +j0.0+j0.0+j0. Only one feeder can be selected at a time to performed series faults. Hence. Default values: Zb=Zn=0.0 For Series Unbalance (phases A. For this tutorial. the “One Phase Open” option is used.Short Circuit Analysis Program ANSI/IEC/IEEE Figure 6: Report Manager for Series Fault Calculation The program allows users to select: one phase (one phase open) two phases open unbalanced series fault At the fault (open location) the user can select the fault impedance in ohms. 19 . The following report will be generated after clicking on the “Analyze” button on the Short Circuit toolbar. 0.48 0.94 -0.C for Two Phases Open Fault Classical Calculation: Complex Z for X/R and Fault Current Transformer Phase Shift is not considered.-------.-------Magn.-------.Unbalance fault ----Item Phase A Phase B Phase C ----.-------.00 Project No.10 Angle -6 -126 113.48 0.00.: Engineer: Jobfile Name: T123 Check by: Scenario : 1 : mode1 Case : 1 : Base -------------------------------------------------------------------------------Electrical One-Line 3-Phase Network for ANSI PDE -------------------Calculation Options -------------------Calculating Series Fault Fault Phases: Phase A for One Phase Open Fault Phase B.48 0.-----------------------.10 0.-------.48 99.48 100.10 0.7 20 and Angle in Degree) .-------.48 0. : Page : 1 Project Name: Date : 10/23/2012 Title : Time : 03:56:14 pm Drawing No.-------From 3C 0. : Company : Revision No.-------. Generator and Motor X/R is constant.0 Fault Impedance(Ohms) : Za = Zb = Zc = Zn = Fault Current Direction : 0 +j 0 +j 0 +j 0 0 0 From Bus --> To Bus Phase Sym Fault Current at 1/2 Cycle (Magnitude in kA ---.05 To 12 0. Base Voltages : Use System Voltages Prefault Voltages : Use Load Flow Results -----------------------------------Feeder/Cable Series Fault Report -----------------------------------Fault Feeder : 3C ->12 Prefault Voltage System Base -------------------------Bus Bus Name kV kV kV % Degree ----.Short Circuit Analysis Program ANSI/IEC/IEEE Paladin DesignBase 3-Phase Short Circuit v7.10 0. 0 Or regardless of the X/R value. For calculating the MF. The tab provides also information on ANSI Standard impedances – first cycle and interrupting cycles: 2-8 cycles as per ANSI/IEEE Std. users can also select: Empirical value for Or = T = 0.5 21 .Short Circuit Analysis Program ANSI/IEC/IEEE 3. the MF is fixed In calculating the MF. users can select: Based on X/R using the equations in section 2.5 AC ANSI/IEEE Standard The AC ANSI/IEEE short circuit analysis method is based on a separate R and X matrix method: Fault current multiplying factors allow setting up marginal coefficients while fault calculations are performed. The Calculation Tab is the same as in AC ANSI/IEEE Standard and provides the same options. The first option uses constant X/R ratio (which is defined in the generator and motor input dialogs).Short Circuit Analysis Program ANSI/IEC/IEEE The short circuit program supports two options for the generators and motors resistances. In the second option. positive). zero. in cycles. the generator/motor resistance is computed from the following X/R ratio: R X" X /R The above resistance is maintained constant for all time bands and sequences (negative. The user can also select the Machine Current Decay. 3. 22 . Fault Current Multiplying Factors allow setting up marginal coefficients while fault calculations are performed.6 AC Classical Short Circuit The AC Classical short circuit analysis method is based on the Complex E/Z calculation method and the X/R ratio is extracted from the complex impedance matrix (X/R). 7 AC IEC 60909 Short Circuit This analysis method is based on the IEC60909 Standard. the generator/motor resistance is computed from the following X/R ratio: R X" X /R The above resistance is maintained constant for all time bands and sequences (negative. the second option. The first option uses constant X/R ratio (which is defined in the generator and motor input dialogs). The Calculation Tab is similar to the AC and ANSI/IEEE Standard and provides the same options. variable X/R (see the lower left part of the above figure).e. positive).Short Circuit Analysis Program ANSI/IEC/IEEE The short circuit program supports two options for generator and motor resistances. zero. 3. Users can select calculations based on different versions of the standard: 1988 Version 2001 Version 23 . In this case the X/R ratio will be variable for different time bands and sequences. i. Method C: applies to the calculation of peak current in mesh networks. zero.1 Method A: uniform ratio R/X.Short Circuit Analysis Program ANSI/IEC/IEEE The short circuit program supports two options for generators and motors resistances. C or Classical Thevenin) Also. Xb from Fig. The first option uses constant X/R ratio (which is defined in the generator and motor input dialogs). This is the case when short circuit currents are calculated at generator terminals. In this case the X/R ratio will be variable for different time bands and sequences. The value of X is calculated from Fig. see the lower left part of the following figure). the control tab allows users to select: Fault Current Multiplying Factors The method employed in calculating the Peak Current (method A.15 multiplied by the X b. In the IEC 60909 short circuit program. In the second option (variable X/R. users can select: System Voltage IEC maximum Voltage IEC minimum Voltage Peak current method: 3. The smallest X/R ratio determines the k factor Method B: applies to the calculation of peak current in mesh networks X=1. B. IEC 60909 and depends on X/R ratio of the network DesignBase Thevenin: X is calculated from the Thevenin equivalent Impedance Correction Factors: Apply K g factor to Generator Z g impedance: This field should be selected when calculating the initial short circuit current in systems fed directly from generators without unit transformers. 8.8 page 47 IEC 60909 Std. positive). the generator/motor resistance is computed from the following X/R ratio: R X" X /R The above resistance is maintained constant for all time bands and sequences (negative. 24 . as per IEC 60909 standard.7. IEC 60909 Std.Short Circuit Analysis Program ANSI/IEC/IEEE The K g factor is given by formula (18) – IEC Std.: KG Un cmax (18.the generator rated voltage X d" - generator sub transient reactance referred to generator rated impedance sin G .generator phase angle between current and terminal voltage 25 .is the system rated voltage U rG .) U rG 1 X d" sin G Where: U n . Short Circuit Analysis Program ANSI/IEC/IEEE Apply Kt factor to network transformer Zt : Users should check the above field if the short circuit occurs from a network transformer. A network transformer (see the figure below) is when a transformer is connecting two or more networks at different voltages (IEC Std.). For two-winding transformers with and without on-load tap-changer, an impedance correction factor KT is to be introduced in addition to the impedance evaluated according to IEC (equation (7) to (9)). K T 0.95 cmax 1 0.6 X T 26 Short Circuit Analysis Program ANSI/IEC/IEEE Where, X T is the relative reactance of the transformer and Cmax is related to the nominal voltage of the network connected to the low-voltage side of the network transformer. This correction factor shall not be introduced for unit transformers of power station units (IEC, see 3.7). This factor is active only if the user selects the “Network Transformer (used in IEC 60909 method)” checkbox in the transformer editor, as shown below: 27 Short Circuit Analysis Program ANSI/IEC/IEEE Apply Adjust Z t factor by using actual tap: If this option is selected, DesignBase adjusts Z T by using actual transformer tap. In this case, the program considers the transformer impedance as a function of the transformer tap position. If the 1988 IEC 60909 version is selected, the “c” factor values are provided by the program, as in table 3: 28 3P3W/4W Other voltage levels 3P3W/4W If the user select the 2001 IEC 60909 version then the “c” factor values are provided by the program.1 1. as follows: cmax cmin Standard: Above 1000 V: A Other 1.05 1 0.05 0.05 1. 3P4W 1 1.95 1 Per user selection per user selection per user selection per user selection per user selection per user selection User Defined: Above 1000 V: Low voltage networks: 230/400V. 3P3W 1.1 1. 3P4W Other voltage levels.Short Circuit Analysis Program ANSI/IEC/IEEE Table 3: IEC c factor cmax cmin Standard: Above 1000 V: Low Voltage networks: 230/400V. 3P3W Other voltage levels.05 1 1 1 Low voltage networks: 230/400V.95 User Defined: Above 1000 V: Other Per user selection per user selection per user selection per user selection 29 . The sub-transient and transient time constants and dc time constants are also considered in the calculations.Short Circuit Analysis Program ANSI/IEC/IEEE 4 AC IEC 61363 SHORT CIRCUIT METHOD IEC 61363 Standard calculates the short circuit instantaneous current as a function of time and displays its instantaneous values. and plot short circuit results varying with time. DesignBase AC IEC 363 Short Circuit program tools are shown below: Options Report Manager Back Annotation Analyze Generators are modeled by their positive sequence sub-transient reactance. open the IEC3632 sample file under the IEC363SC sample folder and then follow the steps below: 1. Launch the short Circuit program. annotate results on the one line diagram. by clicking on the short circuit program icon. and motors are modeled by their locked-rotor impedance. The method provides an accurate evaluation of the short circuit current for sizing protective devices and coordinating relays for isolated systems (off-shore platforms and ships electrical design). and then click on the “Options” icon to open the Short Circuit Analysis Basic Option window. This application allows users to display results in a standard report format. For this tutorial. The machine’s sub-transient reactance and time constants are used by this method. 30 . 2. The Calculation Tab is similar to the AC ANSI/IEEE Standard and provides the same options. The “Options” features are similar to the ANSI Method. Select the “AC IEC 61363” analysis method. Short Circuit Analysis Program ANSI/IEC/IEEE Click “OK”. 31 . and then open the Report Manager. Reports can be set to the following options: Fast User Defined Curve with Time Users can also see and modify: Input Report & Abbreviations: Input Data and Abbreviation.Short Circuit Analysis Program ANSI/IEC/IEEE As can be seen from the window above. Report Style. Units & Log: Print Layout. Unit. View Log File. The AC IEC 61363 Short Circuit program “Abbreviations” are displayed below: 32 . the following dialog window will be displayed: If User Defined Report is selected the additional “User Defined Output Options” will appear: 33 .Short Circuit Analysis Program ANSI/IEC/IEEE If Fast Report is selected. cycle 1 – cycle 3 – cycle 5 . Select Bus B1. click on the “Report Manager” icon. 34 . Then.Short Circuit Analysis Program ANSI/IEC/IEEE Similarly to ANSI and IEC 60909 analysis methods. Fast or User Defined report allow users to select: Time Bands: 0 – cycle ½ .cycle 8 – cycle 30 – cycle User defined output options: Td –DC Time constant. Select “Curve with Time” and then click “OK”. rms value Idc –Short circuit DC component Ienv-Short circuit envelope In order to display Short Circuit Results varying with time. in seconds Iac –Short circuit AC symmetrical component. The following graphs will be displayed: Figure 7: IEC-61363 Short Circuit Chart The following Short circuit components can be individually displayed or in combinations: Idc – dc component of SC Current iac – instantaneous ac component Ienv – Upper Envelope of Sc current I – Instantaneous total short circuit current Im – magnitude of ac component 35 .Short Circuit Analysis Program ANSI/IEC/IEEE Click the analyze icon. All the following steps and explanations are applicable to AC Classical. “Time Bands”. If the fault is at one bus. LL-G. 6 USING DESIGNBASE REPORT MANAGER Open the ANSI-YY sample file located in the short circuit sample folder. L-G. ANSI/IEEE.Short Circuit Analysis Program ANSI/IEC/IEEE 5 AC SINGLE PHASE SHORT CIRCUIT METHOD The AC Single Phase Method is based on the Complex E/Z calculation method and the X/R ratio is extracted from the complex impedance matrix (X/R). Launch the short circuit toolbar. Abbreviation. Unit & Log. Misc. and IEC-60909 short circuit analysis methods. Select the Fault Types as shown below: 3-P. Report Style. L-L. Figure 8: Short Circuit Report Manager 36 . User Defined. the “Branch Contribution” option can be used. PDE. Output Destination: output to CSV or output to Text File Fast Report: Users can select “Fault Type”. Input Data. and click on the report manager Icon The Report Manager provides: Output Reports: Fast. The Calculation Tab is the same as in AC ANSI/IEEE Standard and provides the same options. Time Bands ½ cycle. but additionally users can select the Phase Bus/Branch Components: X/R. AC.Short Circuit Analysis Program ANSI/IEC/IEEE Click “OK” and then run the program by clicking the “Analyze” icon. Asym. proceed as follows: Select Output to CSV or Text File Click on “Browse” icon and assign the path and the file title Click “OK” Then click the “Analyze” icon on the short circuit toolbar 37 . In order to get a tabulated output report. DC. The positive. User Defined Reports: It is similar to the “Fast Report”. The rms short circuit currents values at 1/2 Cycle are calculated at selected buses or at all buses depending on the bus selection (in the short circuit Options dialog or directly on the drawing). Angle. negative. Motors are normally not grounded and therefore the grounding option should be none. and zero sequence sub-transient reactance X” are used in modeling both the generators and motors. Figure 9: Short Circuit Excel Report 38 .Short Circuit Analysis Program ANSI/IEC/IEEE An excel report will be generated under the DesignBase output folder as shown below. Select “Fast” output report.Short Circuit Analysis Program ANSI/IEC/IEEE Professional Report: Open the report manager. The program will display the Report shown below: Figure 10: Short Circuit Professional Report Notes: In all the unbalanced fault calculations it is assumed that the negative sequence impedance of a machine is equal to its positive sequence impedance 39 . ANSI Bus Summary and then click on “Professional Report Writer Wizard”. and transformer grounding types and winding connections are taken into consideration while building up the system positive. negative. and the generators are modeled by their positive sequence transient reactance X’. motor. generators are modeled by their positive. The short circuit current contributions from motors are ignored. and zero sequence sub-transient reactance is used for modeling both the Generators and motors For steady short circuit. negative. negative.Short Circuit Analysis Program ANSI/IEC/IEEE Generator. and zero sequence networks The positive. 40 . and zero sequence reactance Short circuit current contributions from motors are ignored in steady short circuit calculations The rms short circuit currents values after 30 cycles are calculated (as per ANSI/IEEE Standards or IEC 60909 Standard) at selected buses or at all buses based on user bus selection (in the short circuit Options dialog or directly on the drawing). momentary asymmetrical crest. The program calculates momentary symmetrical and asymmetrical rms. and if: I Circuit _ Duty I Equip. The circuit duties are checked against equipment interrupting capabilities. or as a Text Report. The fault study is per the Standard selected by the user: IEEE/ANSI C37 Standard or IEC 60909. fuses. based on user selection.Short Circuit Analysis Program ANSI/IEC/IEEE 7 PROTECTIVE DEVICE EVALUATION (PDE) BASED ON ANSI/IEEE AND IEC-60909 Paladin DesignBase PDE is a fast and accurate tool which evaluates buses and protective devices such as: LV. Some features of the PDE program are: Equipment operating voltage can be set to: o Load Flow calculated Voltage o Actual Voltage o System voltage The PDE program includes CB impedances and CB’s X/R ratio Equipment can be: o Buses (ANSI only) o Protective Devices (ANSI and IEC) Output results can be organized by: o Equipment Input Rated Data o PDE Calculated Data o Circuit Duty calculated data PDE output results are either graphically displayed onto the one line diagram (in green if the equipment passes or in red if they fail). otherwise it fails. and interrupting adjusted symmetrical rms short circuit currents at faulted buses. 41 . interrupting symmetrical rms. MV and HV CBs. and switches based on ANSI/IEEE and IEC Standards. _ Intrr The equipment passes. select “All buses”. protective device evaluation will be done based on branch short circuit current versus total bus fault current. All the following steps and explanations are applicable to both the ANSI/IEEE and IEC-60909 short circuit analysis methods. This option is present in both ANSI/IEEE and IEC-60909. If “Max Branch Fault Flow” is selected under the “Duty Type for PDE”. 42 . In the Short Circuit Analysis Basic Option.Short Circuit Analysis Program ANSI/IEC/IEEE Open the ANSI-YY sample file located in the short circuit sample folder. Note: The “Total Bus Fault Current” method is the most conservative method. the PDE results will be displayed on the one line Diagram. default output “Report”. and then click “OK” as shown below: If “Annotation” is selected as the “Default Output”. select PDE: Click “OK” and then run the short circuit program. The Protective Device Evaluation List shown below will be displayed: Figure 11: Protective Device Evaluation List 43 .Short Circuit Analysis Program ANSI/IEC/IEEE In the Report manager. More details regarding equipment failing and data error can be seen under the “Detailed Report”: Double click on breaker A10 in the equipment list.Short Circuit Analysis Program ANSI/IEC/IEEE Notes: User can select evaluation of branches or buses by toggling the “List Equipment of type” field: In general Data error is displayed if: o The equipment voltage is not equal or lower than the system voltage o The equipment voltage in the editor is zero o The equipment short circuit ratings in the editor are zero or not consistent with their definitions. 44 . Change the Peak current to 50 kA and the data error message will disappear. The Peak closing and latching current is 0 when it should be bigger than the 40 kA Asymmetrical current to be consistent. Short Circuit Analysis Program ANSI/IEC/IEEE Click on “Summary Report” to display the summary report. Figure 12: ANSI PDE Summary Report 45 . size and font color for additional customizations. Font Style.-Fault Voltage/ Residual Voltage Select the unit Fault Current to be displayed Select this option to display the current flow arrows Figure 13: Short Circuit Annotation Window Select the back annotation ON or OFF. Font. 46 . Auto-refresh. click on the Short Circuit Back Annotation icon The Annotation window below will appear: Select this option to display the bus Pre-Fault Voltage Select the color and font size Select this option to display the Fault Branch Current Select this option to display the Bus Sym. To customize the annotation.Short Circuit Analysis Program ANSI/IEC/IEEE 8 SHORT CIRCUIT BACK ANNOTATION Short circuit results can be displayed on the one the one-line diagram by selecting “Annotation” in the short circuit Options. The following networks are represented: a) Model with each motor individually represented b) Model with the three motors in a) combined inside a MCC schedule Double click on the motor “MCC” symbol to see the motors representation inside the schedule.Short Circuit Analysis Program ANSI/IEC/IEEE 9 MANAGING SCHEDULES IN SHORT CIRCUIT CALCULATIONS Schedule is a Paladin DesignBase feature that allows users to combine several motors and loads in a single symbol. Open the “SC_MCC_SCHEDULE” sample file under C:\DesignBase\Samples\3PhaseSC. 47 . Figure 15: Feeder Representation inside a Schedule 48 .Short Circuit Analysis Program ANSI/IEC/IEEE Figure 14: Motors inside schedule Click on the “Prot Dev/Cable” button to see the cables associated with each motor. Figure 17: Motor Loading / Usage inside a schedule 49 .Short Circuit Analysis Program ANSI/IEC/IEEE Click on the “Status” button to switch “ON” or “OFF” motors. Figure 16: Motor Status inside a Schedule Click on the “Usage” button to change each motor percent running. Short Circuit Analysis Program ANSI/IEC/IEEE To display the schedule short circuit results onto the drawing and Report. Fault Type. and Time Band shown below: 50 . Step 2: Open the Short Circuit Basic Option shown below: Step 3: In the Report Manager select the “Fast” report. click on the AC short circuit icon and follow the steps below: Step 1: Select the “MCC” bus symbol. 51 . proceed as follows: Step 5: Open the Report Manager and select “Misc” then “MCC/Schedule.Short Circuit Analysis Program ANSI/IEC/IEEE Step 4: Click the “Analyze” icon and the Short Circuit Results will be displayed onto the drawing: Figure 18: Short Circuit at MCC bus and branch contributions In order to see the detailed short circuit results for each motor inside the “Schedule”. ---------------------X/R Sym Asym X/R X Device Name Status kVA HP Ratio kA kA Ratio (%) ---------------.C for Line-Line or Line-Line-Ground Fault Classical Calculation: Complex Z for X/R and Fault Current Transformer Phase Shift is not considered.-----.----.00 52 Cable Data -----------------Length R X (Feet) Ohms/K Ohms/K -----.----.-----.0433 0. Generator and Motor X/R is constant.-----100 0.3 Phase Faults --------------------------------------------------MCC/Schedule Bus Name : Item ---1 2 3 Cd -MI MI MI MCC Prefault Voltage: 480.0433 0.0338 100 0.0433 0.0338 .------.5 Cycle -.00 17.60 4.----1 200.21 10575 13898 9.-----.97 10100 12633 9.0 V Motor Bus fault Motor Data Rating --------------------.00 2 200.60 4.00 3 100.00 218. Base Voltages : Adjusted by Tap/Turn Ratio Prefault Voltages : Use System Voltages Jobfile Name: SC_MCC_SCHEDULE Page : 2 --------------------------------------------------Bus Schedule Results: 0.00 104.00 218.----.------.Short Circuit Analysis Program ANSI/IEC/IEEE Step 6: Click “Analyze” icon.00000 Ohms Fault Phases: Phase A for Line-Ground Fault Phase B.00 20.00 17.59 6.00000 + j 0.0338 50 0.97 10100 12633 9. The fault results will be displayed as a “Text output Report”: -------------------Calculation Options -------------------Calculating Single Bus Fault with Fault Z = 0. Short Circuit Analysis Program ANSI/IEC/IEEE MCC Schedule Results Validation: Perform short circuit calculation at bus “Motor Bus” and compare it to the results obtained previously at “MCC”. The fault results match in the both motor representation. 53 . A verification and validation is also performed to verify the results.Short Circuit Analysis Program ANSI/IEC/IEEE 10 NETWORK REDUCTION/EQUIVALENT 10. go to File>Open Drawing File>C:\DesignBase\Samples\Network Reduction. GGG138. 10. DesignBase short circuit program allows the computation of network equivalent systems that can be used for any type of fault analysis.axd” will be used. This section illustrates step-by-step instructions on how to compute power system equivalents at given buses. However.1 Introduction In an interconnected power system. Let assume the right part of the system. the part of the system that need to be reduced should be first identified. To open it. need to be replaced by an equivalent at buses BBB138.2 How to Perform Equivalent/Reduction Calculations To perform the equivalent calculation of a power system. it is not necessary to model the entire neighboring system if an exact equivalent representation can be obtained. circled in red blow. and ZZZ69: Figure 19: Part of the System to be Reduced 54 . In this tutorial the sample file “REDUCTION_ORIGINAL. engineers are often required to exchange their system models with their neighboring utilities in order to study the entire system. open the “Report Manager”. and AAA138 ->BBB138 in the original system should be placed out of service to compute an equivalent system seen from buses BBB138. Step2: Specify where the equivalent should be computed. After switching “OFF” the aforementioned feeders proceed as follows: Step1: Launch the short circuit program and select the Options icon as shown below. BBB138. Figure 20: Selecting Buses for Network Equivalence Step3: To obtain a report of the equivalent system at the selected buses. The “Options” of the short circuit program should be set as shown below. ZZZ69.Short Circuit Analysis Program ANSI/IEC/IEEE Feeders ZZZ69->JJJ69. It can be seen that buses GGG139. HHH138->GGG138. AAA69->ZZZ69. and GGG138 without the right side of the network. and ZZZ69 are selected. 55 . choose the “Misc” option. Figure 21: Selecting Network Equivalent Report Option 56 . and then select “Equivalent Sys.Short Circuit Analysis Program ANSI/IEC/IEEE Step4: To select the equivalent system report.” as shown below. Click “OK”. Once the computations are completed. In this example connection between BBB138 and ZZZ69 is a transformer. it is safe to ignore the link.e. generators) represent a part of a complex system. The report contains a set of “Equivalent Generators” that should be placed at the equivalent buses (see column marked as “Type” in the report below toward the bottom). 3) If the impedance value of a link between two buses is extremely high (i. we can proceed to the equivalent computations by selecting the “Analyze” icon. there are equivalent branches (feeder/transformer) that should be connecting the equivalent buses. Also. Again. no coupling between buses). the report of the equivalent system will be displayed. 2) The positive and negative sequence values of the links (feeders/transformers) can be assumed to be the same even though their computed values may not be equal. 57 .Short Circuit Analysis Program ANSI/IEC/IEEE Step5: At this point. the column marked as “Type” shows the links between the equivalent buses as feeder/line or transformers (TRSF). the following can occur: 1) The impedances may have negative resistances and/or reactances. Figure 22: Sample Network Equivalent Report Important Note: Since the equivalent elements (feeders/transformers. Figure 23: Reconstructed System Using the Calculated Equivalent 58 . In order to reconstruct the original system with the equivalent.Short Circuit Analysis Program ANSI/IEC/IEEE 10. the left side of the network) to the new equivalent part.axd” under C:\DesignBase\Samples\Network Reduction. we need to join the part of the system which was not reduced (in our example. Based on the report obtained in the previous section. feeders and transformers).3 Simplifying the Original System by Using the Computed Equivalent As described in the previous section. the data for each equivalent element was used to build the network “Reduction_Equivalent. the equivalent system contains equivalent elements (generators. Short Circuit Analysis Program ANSI/IEC/IEEE Figure 24: Equivalent Generator at Bus BBB138 Figure 25: Equivalent Generator at Bus GGG138 59 . Short Circuit Analysis Program ANSI/IEC/IEEE Figure 26: Equivalent Generator at Bus ZZZ69 Figure 27: Equivalent Feeder between Buses BBB138 and GGG138 60 . Short Circuit Analysis Program ANSI/IEC/IEEE Figure 28: Equivalent Transformer between Buses GGG138 and ZZZ69 Figure 29: Equivalent Transformer Between Buses BBB138 and ZZZ69 61 . and ZZZ69-EQUI. Figure 30: Fault Currents in Original Network 62 . GGG138. the steps below are performed: 1) In the original system (without reduction) compute a three-phase and single line to ground fault at buses BBB138. 3) The results obtained in step 1 should agree with the results obtained in step 2 above. and ZZZ69 2) In the reconstructed system (remaining system joined with the equivalent system compute a threephase and single line to ground fault at buses BBB138-EQUI.Short Circuit Analysis Program ANSI/IEC/IEEE 10.4 Validation and Verification of the Equivalent To verify and validate the network equivalent feature. GGG138-EQUI. Comparative Short Circuit Results and errors in %: Bus Name Pre_Flt Voltage.04 1726 1957 3240 1728 1959 3242 0. in A L.07 0.08 0.G Flt. in % 1272 1464 2644 1273 1465 2645 0. in A Original Net. in V BBB138 GGG138 ZZZ69 138000 138000 69000 3 P Flt.12 0. The errors are less than 0.Short Circuit Analysis Program ANSI/IEC/IEEE Figure 31: Fault Currents the Reconstructed System Comparison of these results shows that the equivalent system was accurately modeled and can be used reliably in short circuit studies.06 63 . Equivalent Net Error. in % Original Net Equivalent Net Error.10 0.3%. Short Circuit Analysis Program ANSI/IEC/IEEE 11 APPENDIX I: SHORT CIRCUIT ANALYSIS INPUT DATA 11.1 Power Grid Input Data Users have the option to input the Power Utility Maximum and Minimum Contribution and the associated X/R ratio. 64 . 2 Synchronous Generator Short Circuit Input Data 65 .Short Circuit Analysis Program ANSI/IEC/IEEE 11. 66 .3 Induction Motor Short Circuit Input Data Whenever there is a schedule. The HP is the average value of the motor in schedules.Short Circuit Analysis Program ANSI/IEC/IEEE 11. User will need to activate this field for all motors fed from VFD. you will see the composition rating on this screen. Motors fed from VFD are not considered during short circuit calculations. 4 Synchronous Motor Short Circuit Input Data Synchronous Motor required data for short circuit calculations 67 .Short Circuit Analysis Program ANSI/IEC/IEEE 11. 5 High Voltage ANSI/IEEE Circuit Breaker Short Circuit Input Data 68 .Short Circuit Analysis Program ANSI/IEC/IEEE 11. 7 Low Voltage IEC Circuit Breaker Short Circuit Input Data 69 .6 Low Voltage ANSI/IEEE Circuit Breaker Short Circuit Input Data 11.Short Circuit Analysis Program ANSI/IEC/IEEE 11. 8 Low Voltage ANSI/IEEE Fuse Short Circuit Input Data 11.Short Circuit Analysis Program ANSI/IEC/IEEE 11.9 Medium / Low Voltage IEC Fuse Short Circuit Input Data 70 . usually two scenarios are considered: Scenario during Power Flow. when the Transfer Switch is “OPEN” Scenario during a Short Circuit downstream UPS source when the Transfer Switch is “CLOSED” These two scenarios can be modeled simultaneously by simply putting the UPS source in “Bypass” mode and specifying the corresponding Bypass Protective Device as shown below: In Bypass mode.Short Circuit Analysis Program ANSI/IEC/IEEE 11. 71 .10 UPS While using UPS units. the fault contribution to a Short Circuit downstream of the UPS unit will only come from the Utility source via the Bypass branch. the fault current has the AC component only.1 Multiplying Factors (MF) The short circuit waveform for a balanced three-phase fault at the terminal bus of a machine is generally asymmetrical and is composed of a unidirectional DC component and a symmetrical AC component. First Cycle (Asymmetrical) Total Short Circuit Current MF (Circuit Duty): Is defined as: MFm 1 2e For: 2 X R .1 X/R = 25. and the amplitude of the symmetrical AC component decays to constant amplitude in the steady-state. If the envelopes of the positive and negative peaks of the current are not symmetrical around the zero axis. The X/R ratio for ANSI breaker duties is calculated from separate R and X networks. The DC component decays to zero. 72 . X/R for ANSI breaker duties are calculated from separate R and X network. the MF is equal to 1.2 where is the instant of time when fault occurs. they are called “Symmetrical”. The MF is calculated based on the X/R ratio and the instant of time that the fault current happens.1 ANSI/IEEE Standard 12.6.Short Circuit Analysis Program ANSI/IEC/IEEE 12 APPENDIX II: THEORETICAL BACKGROUND 12.6 Peak Multiplying Factor Is defined as: MFPeak 2 (1 e 2 X /R ) . Note: In the short circuit option tab “Control for ANSI/IEEE” the user has the option to calculate MFm based on X/R or use MFm=1. If the envelopes of the positive and negative peaks of the current waveform are symmetrical around zero axis. If the DC fault component is not considered in the fault current. then the fault current is asymmetrical and is called asymmetrical or total fault current. and it is symmetrical. they are called “Asymmetrical”.1. The multiplying factors MF converts the rms value of the symmetrical AC component into asymmetrical rms current or short circuit current duty. if DC fault component is considered. 4 * where the EG . “No AC Decay” (NACD) at its initial value or it may reduce with time toward a residual AC current magnitude (ACD). the AC short circuit current decay will be slow and a conservative simplification is to assume that there is no AC decay (NACD) in the symmetrical AC component. Per ANSI Standards: A generator is a LOCAL SOURCE of the short circuit current if: The per unit reactance external to the generator is less than 1.5 times the generator per unit sub transient reactance on a common system base MVA The generator short circuit contribution may be written as: IG EG ( XExternal X d" ) .4 * where the EG .2 Local and Remote Contributions The magnitude of the symmetrical current (AC component) from remote sources remain essentially constant. If the fault is close to a generator.1. and X/R = 25 to one decimal place is Note: In the short circuit option tab “Control for ANSI/IEEE” the user has the option to calculate MFpeak based on X/R or use MFpeak = 2. when a generator is local or close to the faulted point.Short Circuit Analysis Program ANSI/IEC/IEEE For: MFPeak 2. X d" EG is the generator short circuit current for a three-phase fault at its terminal bus X d" 73 . then the AC component decays (ACD).7. 12. X d" EG is the generator short circuit current for a three-phase fault at its terminal bus X d" A generator is a REMOTE SOURCE of a short circuit current if: The per unit reactance external to the generator is equal to or exceeds 1. In other words. 3 Its location from the fault is two or more transformations or Its contribution to the total symmetrical rms Amperes is less than or equal to 0.7 .5 times the generator per-unit sub transient reactance on a common system base MVA Its contribution to the total symmetrical rms Amperes will be greater than 0. If the generator is remote from the faulted point. the short circuit current decays faster. = ½ Cycle. reactors. then NACD 0 12.1 System Parameters Power transformer parameters The impedance module ZT can be calculated from the rated transformer data as follows: 74 . 12. cables and other similar equipment. Z(0) U(0) / I(0) . then NACD 1 When all contributions are local. 6 The zero-sequence short-circuit impedance. positive-sequence and negative-sequence short-circuit impedances are equal: Z (1) Z ( 2 ) . network transformers (T) and power station units (S) will be multiplied with the impedance correction factors KG. feeders. In this case. overhead lines. cable sheath and cable armoring). No AC decay (NACD) Ratio The Total Short circuit Current is equal to: I Total I Local I Re mote 4 and: NACD I Re mote I Total 5 When all contributions are remote. the three-fold zero-sequence current flows through the joint return. earth wire. earthing arrangement. The impedances of generators (G).Short Circuit Analysis Program ANSI/IEC/IEEE The ANSI Standards provide multiplying factors (MF) based X/R ratio for three-phase faults and line-toground faults fed predominantly from generators and MF for faults fed predominantly from remote sources. 7 is determined by assuming an AC voltage between the three paralleled conductors and the joint return (for example earth.2. KT and KS or KSO when calculating short-circuit currents with the equivalent voltage source at the short-circuit location according to the standard [1]. or when there is no generator.2 IEC 60909 While using the IEC standard the following system components formulae are used: The network components like power transformers. neutral conductor. 3 I rT2 9 Where: PkrT is the total loss of the transformer in the windings at rated current. 75 . The positive-sequence short-circuit reactance XT of a two-winding transformer results as follows: X T ZT2 RT2 . . For large transformers. 12 Z(2) : . . Note: The resistance RT is to be considered if the peak short-circuit current ip or the DC component iDC is to be calculated. on the high-voltage or low-voltage side. when calculating short-circuit currents. which is equal to the negative-sequence short-circuit impedance Z T Z (1) Z ( 2 ) .the rated current of the transformer on the high-voltage or low-voltage side. 100 S rT 8 Where: UrT is the rated voltage of the transformer. The positive-sequence short-circuit resistance RT of a two-winding transformer is given by the relationship: RT PkrT .. ukr is the short-circuit voltage at rated current in percent. the resistance is so small that the impedance is represented by the reactance only. IrT . . SrT is the rated apparent power of the transformer. U rT2 11 Note: The ratio RT/XT generally decreases with transformer size. . 10 The relative reactance of the transformer xT is given by the formula xT S rT XT .Short Circuit Analysis Program ANSI/IEC/IEEE ZT u kr U rT2 . The impedance impedance Z (1) ZT of a two-winding power transformer is considered like positive-sequence short-circuit . Short Circuit Analysis Program ANSI/IEC/IEEE The actual data for two-winding transformers (used as network transformers or in power stations) are given in IEC 60909-2. The zero-sequence short-circuit impedance manufacturer: Z ( 0 )T may be obtained from the rating plate or from the Z ( 0 )T R( 0 )T jX ( 0 )T , 13 Zero-sequence impedance arrangements for the calculation of unbalanced short-circuit currents are given in IEC 60909-4. For two-winding power transformers with and without on-load tap-changer, an impedance correction factor KT is to be introduced in addition to the impedance evaluated according to equations (1.2) (1.4): KT 0.95 cmax , 1 0.6 xT 14 where cmax (from table 2.2) is related to the nominal voltage of the network connected to the LV side of the network transformer and the transformer relative reactance is calculated with the relationship (11). The correction factor will not be introduced for unit transformers of power station units. The correction factor KT is multiplying all the components of the transformer positive-sequence impedance, according to the following relationship: Z TK KT Z T KT RT j KT X T , 15 The impedance correction factor will be applied also to the negative-sequence and the zero-sequence impedance of the transformer when calculating unbalanced short circuit currents. If the long-term operating conditions of network transformers before the short circuit are known for sure, then the following equation may be used instead of equation (1.10) in order to calculate the correction factor KT: KT Un cmax , b b U 1 xT I T / I rT sin Tb 16 Where: cmax is the voltage factor from table 1.2, related to the nominal voltage of the network connected to the LV side of the network transformer. Ub - the highest operating voltage before short circuit. I Tb - the highest operating current before short circuit (this depends on network configuration and relevant reliability philosophy). 76 Short Circuit Analysis Program ANSI/IEC/IEEE tb - the angle of power factor before short circuit. The impedance correction factor will be applied also to the negative-sequence and the zero-sequence impedance of the transformer when calculating unbalanced short-circuit currents. The impedances between the star point of transformers and earth are to be introduced as (3 ZN) into the zero-sequence system without a correction factor. The rated transformation ratio tr of the power transformer: tr U rTHV , U rTLV 17 where UrTHV and UrTLV are transformer rated voltages of the HV and LV windings, respectively. Reactors Assuming geometric symmetry, the positive-sequence, the negative-sequence and the zero-sequence shortcircuit impedances of reactors are equal: Z (1) Z ( 2 ) Z ( 0 ) , 18 Short-circuit current-limiting reactors will be treated as a part of the short-circuit impedance. ZR X R ukR U n , 100 3 I rR 19 Where: ukR and IrR are given on the reactor rating plate. UN – the system nominal voltage. Synchronous Generators and Motors The synchronous generator rated impedance is given by: Z rG The relative subtransient reactance x"d 2 U rG ,, S rG 20 , related to the ated impedance is: 77 Short Circuit Analysis Program ANSI/IEC/IEEE X d" , x Z rG " d 21 The following values for the fictitious resistances RGf may be used for the calculation of the peak short-circuit current with sufficient accuracy: X d" for generators with UrG > 1 kV and SrG ≥ 100 MVA; X d" for generators with UrG > 1 kV and SrG < 100 MVA; RGf = 0.07 X d" for generators with UrG ≤ 1 kV. RGf = 0.15 RGf = 0.05 In addition to the decay of the DC component, the factors 0.05, 0.07, and 0.15 also take into account the decay of the AC component of the short-circuit current during the first half-cycle after the short circuit took place. The influence of various winding-temperatures on RGf is not considered. The values RGf cannot be used when calculating the aperiodic component iDC of the short-circuit current. When the effective resistance of the stator of synchronous machines lies much below the given values for RGf, the manufacturer’s values for RG should be used. The subtransient impedance the formula: ZG of the generator, in the positive-sequence system can be calculated with Z G RG jX d" , 22 When calculating initial symmetrical short-circuit currents in systems fed directly from generators without transformers unit, the corrected impedance Z GK of the SG has to be used in the positive-sequence system: Z GK K G Z G K G RG j K G X d" , 23 with the correction factor KG for SG, given by the relationship: KG cmax U n , 1 x sin rG U rG " d where: cmax is the voltage factor according to table 2.2. UN - the nominal voltage of the system. 78 24 If the terminal voltage of the generator is different from UrG. and the steady-state short-circuit current Ik. for the negative-sequence reactance SM. in the negative-sequence system. For the short-circuit impedance from equation (1. it may be necessary to introduce: U G U rG 1 pG .the rated voltage of the generator. their arithmetical mean can be used: X ( 2)G X d" X q" 2 The corrected short-circuit impedance of SG. following equation: . X" 25 X" q d and If the values of reactances are different. I" When calculating the initial symmetrical short-circuit current k .20): X ( 2 )G 27 of SG in the zero-sequence system. synchronous compensators are treated in the same way as SG. they are subject to additional considerations. U I rG . If not. 79 . the following applies with KG Z ( 0 )GK K G R( 0 )G jX ( 0 )G . The correction factor KG (equation 24) for the calculation of the corrected subtransient impedance cU / 3 Z GK has n been introduced because the equivalent voltage source is used instead of the subtransient voltage E″ behind the subtransient reactance of the synchronous generator.Short Circuit Analysis Program ANSI/IEC/IEEE x"d . by the Z ( 2)GK K G RG j K G X ( 2)G . the symmetrical short-circuit breaking current Ib. Z ( 0 )G of the 26 Z ( 2 )GK . rG is the phase angle between rG and UrG . according to the (21) relationship. 28 When an impedance is present between the star-point of the generator and earth. they are treated like synchronous generators. If synchronous motors have a voltage regulation. is given. the correction factor KG will not be applied to this impedance. the peak short-circuit current ip.the relative subtransient reactance of the generator related to the rated impedance. The contribution of AM in LV power supply systems to the short-circuit current I k" may be neglected if their I" contribution is not higher than 5 % of the initial short-circuit current k 0 M . those MV and LV motors may be neglected. 31 Where: I rM is the sum of the rated currents of motors connected directly (without transformers) to the network where the short-circuit occurs.05 I k 0 M . MV motors have to be considered in the calculation of maximum short-circuit current. for example in networks of chemical and steel industries and pump stations. providing that. they are not switched in at the same time.the initial symmetrical short-circuit current without influence of motors. for unbalanced short circuits. according to the circuit diagram (interlocking) or to the process (reversible drives). calculated without motors: " I rM 0. The rated current of the AM is given by the relationship: I rM 3 U rM PrM . I k" 0 M . The impedance module ZM of AM in the positive. LV motors are to be taken into account in auxiliaries of power stations and in industrial and similar installations. to the symmetrical short-circuit breaking current Ib and. I" MV and LV motors contribute to the initial symmetrical short-circuit current k . cos rM 29 where PrM. rated power factor and rated efficiency of the motor. cosrM and rM are respectively the active rated power. in accordance with its nameplate data. In the calculation of short-circuit currents.Short Circuit Analysis Program ANSI/IEC/IEEE Asynchronous Motors (AM) The rated apparent power of an AM can be calculated from the equation: S rM rM PrM . to the peak short-circuit current ip. also to the steady-state short-circuit current Ik. rM cos rM 30 where UrM is the rated line voltage of the AM.and negative-sequence systems can be determined by: 80 . Short Circuit Analysis Program ANSI/IEC/IEEE Z rM S rM 2 U rM . 34 For the determination of the initial short-circuit current according to the short-circuit currents calculation method.the ratio of the locked-rotor current to the rated current of the motor. may be neglected in the calculation of short-circuit currents for a short-circuit at the feeder connection point Q.989ZM for MV motors with rated powers per pair of poles (PrM/p)<1 MW. RM/XM=0. RM/XM=0. 33 However the motor resistance RM will be RM X M RM / X M . where p is the pair of poles number.15. Z M RM jX M" . MV and LV motors. if there is the following condition: 81 . SrM . with connection cables. AM are substituted by their impedances systems: ZM . If the ratio (RM/XM) is known. The following relations may be used with sufficient accuracy in order to calculate AM parameters: RM/XM=0. with XM=0. then the motor reactance XM will be calculated as follows: XM ZM 1 RM / X M 2 . with XM = 0.the rated apparent power of the motor (see relationship (1.10. (ILR/IrM) .922ZM for LV motor groups.42.25)). in the positive-sequence and negative-sequence 35 The zero-sequence system impedance Z(0)M of the motor will be given by the manufacturer. if needed.995ZM for MV motors with rated powers per pair of poles (PrM/p)≥1 MW. I LR / I rM 32 Where: UrM is the rated voltage of the motor. which are connected by two-winding transformers to the network in which the short circuit occurs. with XM=0. 34 31 Cu ' The effective resistance per unit length RLr of overhead lines at the conductor temperature 20°C may be calculated from the nominal cross-section qn and the resistivity ρ: ' RLr qn . 38 The line resistance RLr at the reference temperature θr=20C can be determined if its length lL is known: 82 . / m.the sum of the rated apparent powers of all transformers. UnQ . 37 may be calculated from the conductor data. 54 1 1 Al mm2 / m for Aluminum and Ala mm2 / m for Aluminum alloy.8 PrM S rT 100 c S rT " 3 U nQ I kQ . Z L RL jX L . qn and the centre-distances d of the The following values for resistivity may be used: 1 mm2 / m for Copper. S rT .the initial symmetrical short-circuit current at the feeder connection point Q without supplement of the motors. such as the cross-section conductors.the nominal voltage of the system at the feeder connection point Q. Lines Constants The positive-sequence short-circuit impedance. 36 0.3 Where: PrM is the sum of the rated active powers of the medium-voltage and the low-voltage motors which will be considered.Short Circuit Analysis Program ANSI/IEC/IEEE 0. through which the motors are directly fed. " I kQ . r . from: d 1 X L' 0 f ln .004 K-1 is the temperature factor of resistivity. 41 Where: dL1L2. 40 Where: α=0. r 4n Where: 83 43 .Short Circuit Analysis Program ANSI/IEC/IEEE ' RLr RLr lL . the equivalent radius rB can be determined by the following formula: rB n n r R n1 . The reactance per unit length X L' for overhead lines may be calculated.the reference conductor temperature in degrees Celsius. line conductors and neutral conductors) will be introduced at a higher temperature e r . when calculating minimum short-circuit currents: RL 1 e r RLr . θe . θr=20C . see also IEC 60865-1.the radius of a single conductor. .the resistance value at a reference temperature of 20°C. IEC 60949 and IEC 60986). 42 Where: n is the number of bundled conductors. valid with sufficient accuracy for most practical purposes for copper. dL2L3 and dL3L1 are geometric distances between conductors. RLr . 39 Line Resistances RL (overhead lines and cables. assuming transposition. aluminum and aluminum alloy. is determined by the relationship: d 3 d L1L 2 d L 2 L3 d L3L1 . or the center of bundles. In the case of bundle conductor. in the case of overhead lines. R is the bundle radius (see IEC 60909-2).the conductor temperature in degrees Celsius at the end of the short-circuit duration (for θe. The geometric mean distance between conductors. from the (43) relationship.the radius of a single conductor or. or n=1 for a single conductor. d . r is to be substituted by rB.85 E 0 . according to (2. However. from textbooks or manufacturer’s data. Z ( 0 ) R( 0 ) jX ( 0 ) . Where: 84 48 . Z Z The impedances ( 1 ) L and ( 0 ) L of LV and HV cables depend on national techniques and standards and may be taken from IEC 60909-2. in the case of conductor bundles. the impedance of a network feeder at the connection point Q is given by: ZQ where 2 c U nQ S " kQ c U nQ " 3 I kQ . . 46 (see IEC 60909-4). 45 and the zero-sequence short-circuit impedance. f – the nominal frequency of the power system. Earth Wire Impedance The equivalent earth penetration depth is given by the following relationship: 1. like in the resistance case. if its length l L is done: X L X L' l L .the geometric mean distance between conductors. n . 44 For measurement of the positive-sequence impedance Z ( 1 ) R( 1 ) jX ( 1 ) . Sometimes it is possible to estimate the zero-sequence impedances with the ratios R(0)L/RL and X(0)L/XL (see IEC 60909-2). The overhead line reactance XL follows to be determined.the number of bundled conductors.Short Circuit Analysis Program ANSI/IEC/IEEE μ0 = 4π10-7 H/m. 47 " I kQ is the initial symmetrical short-circuit current. m. r .37) relationship. for Steel wires. if there are two earth wires: 85 .06 / km .500 3 3 (5.2)10 70200 50100 Clay. Resistivity E and equivalent earth penetration depth for different soil types Table 4: Resistivity and equivalent earth penetration Resistivity E.32)10 660930 (1. rWW .781.711.945. ν . μr ≈ 5 .2)10 3 3 (2. ω= 2πf .19. having values in accordance with table 2. 0 μr .1 content.1)10 (2.the earth wires number. m Earth types 4 Granite Rocks Stony soil >10 3 (310)10 3 (13)10 Pebbles. loam Marshy soil 3 1050 <20 Equivalent earth penetration depth . 10.22)10 3 (0.22.equivalent earth wire radius. wet sand Farmland (0. μr ≈ 75. 0.3)10 (4.300 >8..05 / km . 49 Where: RW' is the earth wires resistance per unit length.323.relative permeability of earth wire. for f 60 Hz.658.21. 50 and calculated with following formula.angular frequency. equal to the earth wire radius rW if there is just one earth wire rWW rW . for other ACSR wires.694. for f 50 Hz. 8 0. m f=50 Hz f=60 Hz >9.2)10 600850 295660 <415 270600 <380 ' The earth wire impedance per unit length Z W is: Z W RW' ' 0 j 0 f r ln 8 rWW 4 .. For Aluminum core steel reinforced (ACSR) wires with one layer of aluminum.Short Circuit Analysis Program ANSI/IEC/IEEE E is the earth type resistivity. dry sand Calcareous soil. μ0 = 4π10−7 H/m – vide absolute magnetic permeability. μr ≈ 1.65)10 3 3 (1.94)10 3 (0. 10 Tolerance.95 1. 54 when there are two earth wires. Sources As per IEC 60909 the equivalent voltage source (rms) is given by the relationship U es c U n 3 .10 86 - .35kV 1.Short Circuit Analysis Program ANSI/IEC/IEEE rWW rW dW . U n 1. 53 when there is only one earth wire and by the next formula dWL 6 dW 1L1 dW 1L 2 dW 1L3 dW 2 L1 dW 2 L 2 dW 2 L3 .1000kV Voltage factor c for the calculation of Minimum short-circuit Maximum short-circuit 1) currents. L2 and L3. V. cmin currents.05 0. given by the formula dWL 3 dWL1 dWL2 dWL3 . % 6 10 Medium voltage.00 1. V Low voltage. cmax 1. having values according to the table 4: Table 5: IEC voltage factor Nominal voltage U n. 51 where dW is the distance between two earth wires. The mutual impedance per unit length between the earth wire and the parallel line conductors with common earth returns Z WL ' 0 j 0 f ln 8 dWL . 52 Where: dWL is the geometric mean distance between the earth wire and the line conductors L1. 55 where c is the voltage factor. U n 100. 12. synchronous and asynchronous machines are replaced by their internal impedances The equivalent voltage source is the only active voltage of the system When calculating short-circuit currents in systems with different voltage levels.the aperiodic DC component beginning with an initial value A and decaying to zero Single-fed short circuits supplied by a transformer may be regarded as far-from.e. U rTHV / U rTLV U nHV / U nLV . which differ in their magnitude. there is no change: o in the involved network o in the type of short-circuit involved Additional calculations about all different possible load flows at the moment of the short-circuit are superfluous General rules All network feeders. system no transformation is necessary if these systems are coherent. 56 for each transformer in the system with partial short-circuit currents. two short-circuit currents. usually to that voltage level at which the short-circuit current is to be calculated For p.u. In the case of a far-from-generator short circuit.generator short circuits if 87 . are neglected Arc resistances are not taken into account For the duration of the short-circuit. voltages and currents are to be converted by the rated transformation ratio tr.9U m should be applied. the short-circuit current can be considered as the sum of the following two components: . In general. U n 35 kV 1) cmaxUn should not exceed the highest voltage Um for equipment of power systems: cmax U n U m .Short Circuit Analysis Program ANSI/IEC/IEEE 2) High voltage .2 Short Circuit Current Calculus Assumptions All line capacitances and shunt admittances are neglected Non-rotating loads.. the square of the rated transformation ratio tr. it is necessary to transfer impedances values from one voltage level to another.the AC component with constant amplitude during the whole short-circuit . i. The impedances of the equipment in superimposed or subordinated networks are to be divided or 2 multiplied by (tr) . 2) if no nominal voltage is defined U m cmaxU n or cminU n 0. except those of the zero-sequence system. are to be calculated.2. " For the calculation of the initial symmetrical short-circuit current I k the symmetrical short-circuit breaking current Ib. it is of interest not only to know the initial symmetrical short-circuit current I k" and the peak short-circuit current ip. 57 with XQt calculated in accordance with 11 and X TLVK KT X TLV . 58 In the case of a near-to-generator short circuit. From the calculated initial symmetrical short-circuit current and characteristic curves of the fuses or current-limiting circuit-breakers. the initial symmetrical short-circuit current is first calculated as if these devices were not available. it is necessary to distinguish between networks with and without parallel branches. This procedure is not allowed when calculating the peak short-circuit current ip. the cut-off current is determined. as the individual contributions to a balanced short circuit can be evaluated separately for each source. When sources are distributed in meshed network and for all cases of unbalanced short-circuits. Normally. and zero-sequence short-circuit impedances of the system. network reduction is necessary to calculate short-circuit impedances Z ( 1 ) Z ( 2 ) and Z ( 0 ) at the short-circuit location. negative-sequence. and the steady-state short-circuit current Ik at the short-circuit location. the symmetrical short-circuit breaking current Ib is smaller than the initial symmetrical short-circuit current I k" . In this case.Short Circuit Analysis Program ANSI/IEC/IEEE X TLVK 2 X Qt . Short-circuits may have one or more sources. In this case. Calculations are simplest for balanced short circuits on radial systems. the system may be converted by network reduction into an equivalent short-circuit impedance Zk at the short-circuit location.the AC component with decaying amplitude during the short circuit .the aperiodic DC component beginning with an initial value A and decaying to zero In the calculation of the short-circuit currents in systems supplied by generators. 88 . which is the peak short-circuit current of the downstream substation. While using fuses or current-limiting circuit-breakers to protect substations. power-station units and motors (near-to-generator and/or near-to-motor short circuits). the short-circuit current can be considered as the sum of the following two components: . The type of short circuit which leads to the highest short-circuit current depends on the values of the positive-sequence. but also the symmetrical short-circuit breaking current Ib and the steady-state short-circuit current Ik. the steady-state short-circuit current Ik is smaller than the symmetrical shortcircuit breaking current Ib. resistances RL of lines (overhead lines and cables.5 and 1 .motors will be neglected . 60 The initial symmetrical short-circuit current I k" I k" c U n 3 Rk2 X k2 .motors will be included if appropriate in accordance with 2. because for the common case Z( 0 ) Z( 1 ) Z( 2 ) . 61 89 .voltage factor cmax . the highest initial short-circuit current I kE 2 E will occur for a line-to-line short circuit with earth connection.4. 59 For short-circuits near transformers with low zero-sequence impedance. In that " case. it is necessary to introduce the following conditions: . Z ( 2 ) Z (1) . Z(0) may be smaller than Z(1).choose the system configuration and the minimum contribution from power stations and network feeders which lead to a minimum value of short-circuit current at the short-circuit location . and neutral conductors) will be introduced at a higher temperature Initial symmetrical short-circuit current The highest initial short-circuit current will occur for the three-phase short circuit. 2. line conductors. will be applied for the calculations of maximum short-circuit currents in the absence of a national standard .choose the system configuration and the maximum contribution from power plants and network feeders which lead to the maximum value of short-circuit current at the short-circuit location.lines resistance RL are to be introduced at a temperature of 20°C When calculating minimum short-circuit currents.voltage factor cmin for the calculation of minimum short-circuit currents will be applied according to table 3 . it is necessary to introduce the following conditions: .Short Circuit Analysis Program ANSI/IEC/IEEE Maximum and minimum short-circuit currents When calculating maximum short-circuit currents.when equivalent impedances ZQ are used to represent external networks. This situation is described by the following relationships: Z( 2 ) / Z( 0 ) 1. or for accepted sectioning of the network to control the short-circuit current . the minimum equivalent short-circuit impedance will be used which corresponds to the maximum short-circuit current contribution from the network feeders . 63 The impedance of the network feeder Z Qt RQt jX Qt is referred to the voltage of the transformer side connected to the short-circuit location. 64 may be neglected.. 67 where the factor κ will be calculated by the following expression: 90 . the contribution to the peak short-circuit current from each branch can be expressed by: i p 2 I k" . it is generally necessary to determine the short-circuit impedance Z k Z (1) . delta-star transformation) using the positivesequence short-circuit impedances of electrical equipment. The impedances in systems connected through transformers to the system. Resistances Rk Rk 0. 66 by network reduction (series connection. the initial symmetrical short-circuit current I k" at the short-circuit location F is the sum of the individual branch short-circuit currents. If there are several transformers with slightly differing rated transformation ratios (trT1. trTn).3 X k . have to be transferred by the square of the rated transformation ratio. 62 X k X Qt X TK X L . and the sources are unmeshed. trT2. 65 In meshed networks.. in between two systems.Short Circuit Analysis Program ANSI/IEC/IEEE where Rk and Xk are the sum of the series-connected resistances and reactances of the positive-sequence system respectively: Rk RQt RTK RL . the arithmetic mean value can be used. Each branch short-circuit current can be calculated as an independent single-source three-phase short-circuit current in accordance with equation: I k" c U n 3 Rk2 X k2 . in which the short-circuit occurs.. parallel connection.. The peak short-circuit current For three-phase short-circuits fed from non-meshed networks. When there is more than one source contributing to the short-circuit current. 98 e 3( R / X ) . according to IEC 60909-0/2001-07 1. the decay to the symmetrical short-circuit breaking current is taken into account by the factor μ according to equation: I b I k" . 70 Where: I k" is the initial symmetrical short-circuit current f . 71 For a near-to-generator short circuit.the time R/X .the resistance/reactance ratio Note: The correct resistance RG of the generator armature should be used and not RGf. 91 .02 0. is the sum of the partial short-circuit currents: i p i pi . fed from sources which are not meshed with one another. I b1 I k"1 . 69 i DC component of the short-circuit current The maximum DC component iDC of the short-circuit current may be calculated with sufficient accuracy by equation: id . in the case of a single fed short-circuit or from non-meshed networks. I b 2 E I k" 2 E . For far-from-generator short circuits.c . I b 2 I k" 2 . the short-circuit breaking currents are equal to the initial short-circuit currents: I b I k" . 68 The peak short-circuit current ip at a short-circuit location F.Short Circuit Analysis Program ANSI/IEC/IEEE 1. 2 I k" e 2f t ( R / X ) . 72 " where the factor μ depends on the minimum time delay tmin and the ratio I kG / I rG and IrG is the rated generator current. Symmetrical short-circuit breaking current The breaking current at the short-circuit location consists in general of a symmetrical current Ib and a DC current iDC at the time tmin For some near-to-generator short circuits the value of iDC at tmin may exceed the peak value of Ib and this can lead to missing current zeros.the nominal frequency t . in Cycles S 1. Table 6: CB rated interrupting time in cycles Circuit Breaker Rated Interrupting Time. The typical total rated interrupting time for MediumVoltage Circuit Breakers is 5 cycles (ANSI C37.0 S is the breakers’ asymmetrical capability factor and is determined based on the rating structure to which the breaker was manufactured.1 Standard Ratings for HV and MV Circuit Breakers (CB) The ANSI/IEEE Standards define the CB total interrupting time in cycles.2 1. 73 i The short-circuit breaking current Ib in meshed networks will be calculated by: I b I k" .06 – 1987). Most breakers manufactured after 1964 are breakers rated on a ‘symmetrical’ current basis. 12.3 ANSI/IEEE Standard Based Device Evaluation (PDE IEEE) 12.5 2 3 4 1. However. However. Peak (Crest) 3. 74 which is usually greater than the real symmetrical short-circuit breaking currents. Both the symmetrical and total current rated breakers have some DC interrupting capability included in their ratings and it is a matter of how it is accounted for in the total interrupting current.0 Medium voltage breakers duty is based on: 1. in Cycles 2 3 5 8 CPT. Momentary Duty Calculation (C & L): 92 .Short Circuit Analysis Program ANSI/IEC/IEEE For three-phase short circuits in non-meshed networks. The interrupting rating is calculated differently based on the formulae shown in the next sections. the Contact Parting Time (CPT) needs to be known for application of breakers. Interrupting The Momentary and Peak formulae apply to both breakers symmetrical and total current rated breakers.3. in the 2 -8 cycle network. the MV CBs interrupting time correspond to 3 cycle contact parting time for the short circuit current. the symmetrical breaking current at the short-circuit location can be calculated by the summation of the individual breaking current contributions: I b I bi .1 1. Momentary rating (C&L) 2. Those manufactured before 1965 were rated on a ‘total’ current basis. Note: For circuit breakers rated on Total Current S=1.4 1. asym.rms rating Peak Duty calculation (Crest): 1. 75 Note: In the short circuit option tab “Control for ANSI/IEEE” the user has the option to calculate MFm based on X/R or use MFm=1.rms). The closing and latching capability of a symmetrical current-rated CB is expressed in terms of Asymmetrical. 2. where: -2 MFm 1 2e X / R .asym = MFm*Isym.rms.rms ) value: If Device C&L.rms.6 3. DesignBase uses the following steps to calculate the circuit breaker momentary duty: 1.rms where: MFp (1 e -2 X /R ) 2 .49 .Short Circuit Analysis Program ANSI/IEC/IEEE The CB Closing and Latching Capability defines the CB ability to withstand (close and immediately latch) the maximum value of the first-cycle short circuit current.rms rating Imom.rms. Compare Imom. Calculate the ½ cycle interrupting short circuit (Isym. Calculate the % Rating = (Imom. Calculate asymmetrical current value using the following formula: Imom.76 and 0.1* e -X/R 3 77 93 . or peak current. Calculate the peak value of momentary SC using the following formula: Imom. 2.peak = MFp*Isym. Calculate the ½ cycle symmetrical short circuit (Isym.asym*100)/Device C&L. Total rms current.rms.rms.0.asym against the medium voltage circuit breaker (C&L. then the device Pass or otherwise it fails 4.rms). There are three options: “All Remote” i. Calculate NACD (No AC Decrement) ratio NACD 4. or otherwise it fails 4.peak against the medium voltage circuit breaker (Creat.peak. NACD = 0 “Adjusted”. Iremote (Itotal . i.7. NACD = 1.5-4) cycle network impedance 3.peak*100)/Device Crest. 3. this is based on actual calculations 1. Compare Imom. Calculate The % rating = (Imom. This is the most conservative solution “All Local”.e. If Device Creast. total local contribution.0.Short Circuit Analysis Program ANSI/IEC/IEEE Note: In the short circuit option tab “Control for ANSI/IEEE” the user has the option to calculate MFpeak based on X/R or use MFpeak = 2. or MFl) Remote – If Generator current contribution to fault is less than 40% of a generator terminal fault then this generator is Remote.peak ) value. For remote fault the multiplying factor is MFr: -4 MFr 1 2e X / R S C 80 94 .e. or equivalent impedance to generation terminals is > 1.5-4 cycles short circuit current. Calculate total remote contribution.peak rating Imom.5 times the Generator Z’’dv.Ilocal) Itotal (Iremote Ilocal) 79 Calculate the Multiplying factor based on the fault location (MFr.peak rating Interrupting Duty Calculation The Maximum Symmetrical Interrupting Capability for a Symmetrical Current-Rated CB is the maximum rms current of the symmetrical AC and DC component. The interrupting fault currents for the MV & HV circuit breakers is equal to 1. Determine if the generator is Local or Remote 2. then the NACD (the current is obtained by using the (1. then the device pass. For a system other than of 60 Hz adjust the calculated X/R as follows: ( X / R) mod (X/R) * 60 System Frequency (Hz) 78 The following steps are used to calculate the circuit breaker interrupting. which the CB can interrupt regardless of how low the operating voltage is. 0.sym Device Int Rating * Rated Max kV * Device Max Int Rating) Operating Voltage kV Compare Iint against the CB 3P Device Duty.007473(X/R) + 0.0. Calculate 3 phase Device Duty by adjusting the device interrupting duty based on rated voltage using the following formula: 3P Device Duty Min ( 7.أ. 8.0000611(X/R) .00002945(X/R) .0.0604 .sym Mixed local and remote: 6. Iint = AMFi*Iint. Calculate Iint.0000002427(X/R) 2 3 1.0. then the device Passes.00006919(X/R) .0494 .rms. The equations are not given in ANSI C37.101. 81 where: Table 7: K factor 1.0 5.rms.Short Circuit Analysis Program ANSI/IEC/IEEE Where C = CB Contact Parting Time in Cyc.0 then the program uses 1. -4 MFl K 2 2e X / R S C .00833(X/R) + 0. Calculate % rating = (Iint *100)/ (3P Device Duty) 95 .0.0.5 2 3 4 K= 2 3 1.rms. otherwise it Fails.1 CPT 1.0000002248(X/R) The Adjusted Multiplying Factor (AMFi) is equal to: AMFi = MFl +NACD (MFr-MFl). All Remote: All Local: Iint = MFr*Iint.0. Local – For any local fault the multiplying factor MFl is calculated using the following formula within DesignBase or look up tables.0278 . If 3P Device Duty Iint.0370 .0. 82 If AMFi is less than 1. but are empirical equations to match the curves within the ANSI breaker standard.008148(X/R) + 0.00006253(X/R) .sym Iint = MFl*Iint.1.000000075638(X/R) 2 3 1.004288(X/R) + 0.000000068368(X/R) 2 3 1. 3.2 Standard Ratings for Low Voltage Circuit Breakers (LV-CBs) For Low-Voltage CBs (LV-CBs) the time of short circuit current interruption occurs within the sub transient time interval.18 4.000 A Test %PF 15 20 Test X/R 6. ICCB rated > 20.59 4. 96 84 . ICCB rated 10. the interrupting capabilities of unfused LV-CBs are sensitive to the maximum peak magnitude of the total /asymmetrical fault current. ICCB (Insulated Case CB) Molded Case (MCCB). 83 Unfused PCB / MCCB / ICCB with Instantaneous setting LVFp (1 e - (1 e 2 πτ X/Rcalc 2 πT X/Rtest ) ) .rms). MCCB. 2.73 3. ICCB rated 10.000 A Molded Case (MCCB).90 The following steps are used to calculate the low voltage circuit breaker interrupting: 1. Calculate Low Voltage Multiplying Factor (LVF) PCB: Power Circuit Breaker ICCB: Insulated Case Circuit Breaker Fused PCB / MCCB / ICCB LVFasym (1 2e - (1 2e - 2 Calc X/R 2 Test X/R ) ( EQ 7) ) .Short Circuit Analysis Program ANSI/IEC/IEEE 12.9 50 30 20 1. However. If the device library does not have a value for X/R then the following default values are used as default by the program: Table 8: Default Device X/R Values Using DesignBase’s Library Breaker Type Unfused Power Circuit (PCB) Breaker Fused Power Circuit Breaker. Calculate the ½ cycle interrupting short circuit (Isym.001-20.000A Molded Case MCCB). Short Circuit Analysis Program ANSI/IEC/IEEE Where 0. LVFasym (1 2e - 4t X/Rcalc (1 2e - 4t X/Rtest ) ) 85 Where t is the breaker minimum short time trip in cycles at interrupting duty.49 . Therefore the LVFp and LVFasym are calculated. The peak interrupting rating is calculated as follows: LVFp (1 e - (1 e 2 πτ X/Rcalc 2 πT X/Rtest ) ) 86 Where 0.1e .X/Rtest 3 In Options of the short circuit Tab “Control for ANSI/IEEE” .49 .1e . Unfused PCB without Instantaneous setting If the breaker does not have an instantaneous setting then the breaker has two interrupting rating (peak and asymmetrical).49 .1e -X/Rcalc 3 and T 0. the user can select to use =T = 0.0.5 Cycles”.5 instead of using the empirical formula by selecting “Applies 0.0.0. The default value used by DesignBase is 3 cycles.X/Rtest 3 97 .0.1e -X/Rcalc 3 and T 0.49 . adj = MFasym*Isym(1/2 Cyc) If the fuse is symmetrical rated.adj against the CB symmetrical interrupting rating. If any of the LVF is less than 1.rms (the ½ cycle interrupting short circuit) 5. then MFasym is calculated using the following formula: 98 .Short Circuit Analysis Program ANSI/IEC/IEEE 3.0 4. In some rare cases the fuse asymmetrical rating is provided. and Switches The LVFs interrupting capability is the maximum symmetrical rms current which the fuse can interrupt and still remain intact.rms (the 3-8 cycle interrupting short circuit) Unfused Breakers With Inst Iint.3 Standard Ratings for Low/High Voltage Fuses.adj = LVFp* Isym.3.adj = LVFasym* Isym.adj = LVFasym* Isym. 4. Evaluation procedure: 3. Compare Iint.adj = LVFp* Isym. While the fuse has a symmetrical current rating it can also interrupt the DC component up to a value based on its test X/R ratio. If Device Symmetrical rating Iint.rms).adj.rms (the 3-8 cycle interrupting short circuit) Iint. Calculate the ½ cycle interrupting short circuit (Isym. Calculate The % rating = (Iint.0 then uses 1. The interrupting capabilities of LV-Fs are classified by the UL according to symmetrical current ratings in rms Amperes.rms (the ½ cycle interrupting short circuit) Unfused Breakers Without Inst Iint.adj*100)/Device Symmetrical rating 12. or otherwise it fails 6. Calculate Iasym: Iasym. Calculate adjusted Interrupting factor Fused Breakers Iint. then the device passes. then the device Pass otherwise it Fails 6. Note: For standard switches the same formulae are used 99 . If Device Symmetrical rating Iasym.Short Circuit Analysis Program ANSI/IEC/IEEE MFasym (1 2e - 2 X/R ) 87 If the fuse is asymmetrical rated. Compare Iasym. Calculate The % rating = (Iasym.adj against the fuse symmetrical interrupting rating.adj*100)/Device Symmetrical rating. then MFasym is calculated using the following formula: MFasym (1 2e (1 2e - 2 Calc X/R 2 Test X/R ) ) . 88 5.adj. ANSI Standard.adj*100/ Device rating Is Device Symmetrical rating greater or Equal to Iint. (X/R)mod=(X/R)*60/(System Hz) For LVCB. MCCB.59 MCCB.73 = 3. selected: Calculate MF based on EQ-1 MVCB Fused? NO YES Fuse / Switch Asymmetrical Rating selected: Calculate MF based on EQ-10 Yes CB X/R is known? CB X/R is known? NO NO The X/R is equal to: The X/R is equal to: PCB.rms). ICCB = 6.Short Circuit Analysis Program ANSI/IEC/IEEE ANSI DEVICE EVALUATION Perform Short-Circuit Study & Update Answer File. Calculate LVF based on EQ-7 For PCB without instantaneous use EQ-8 & EQ-9 Go to Page 2 IF LVF < 1. For frequency other than 60 Hz.001-20.rms(3-8 Cyc) NO Pass Fail Calculate %rating=Isym. ICCB rated > 20.adj*100/ Device rating Figure 32: Device Evaluation.000A MCCB.adj =LVFp*Isym. Part 1 100 YES PCB.adj =LVFasym*Isym.rms. then LVF =1 Is Device rating greater or Equal to Iasym.000 A = 1.rms(½ Cyc) int.18 = 4.adj? Yes Pass Fail Calculate %rating=Iint. MVCB & Fuses Calculate the ½ cycle short-circuit current (Isym. ICCB rated <=10. Run the PDE analysis Fuses/ Switches LVCB Fuse / Switch Symmetrical Rating.sym. then adjust the X/R where.adj? Yes NO MCCB/ICCB/PCBWith Instantaneous : Iint. ICCB rated 10.000 A MCCB.rms PCB Without Instantaneous: Iint.adj =LVF*Isym. ICCB = 4. MCCB and ICCB.9 Calculate LVF based on EQ-8 for PCB breaker with Instantaneous Setting.9 . For MVCB calculate the Iint. rms.6 MFp = 2.sym Is Device peak (crest) rating greater or Equal to Imom.asym*100/ device C&L.sym/S Yes NO Is Device Int rating greater or Equal to calculated Iint? Calculate %rating=Imom.rms.rms rating greater or Equal to Imom.rms.0 Iint = AMFi*Iint. Part 2 101 Momentary Duty (C&L) Is Device C&L.sym All Local Calculate MFp using EQ-2 Calculate MFm using EQ-1 Calculate Imom. If AMFl less than 1 use 1.rms.rms Calculate MFl using EQ-5 Iint=MFl*Iint.rms.peak? NACD Calculate: NACD using EQ-3 MFr using EQ-4 MFl using EQ-5 AMFi = using EQ-6.Short Circuit Analysis Program ANSI/IEC/IEEE MVCB From Page 1 ANSI DEVICE EVALUATION Page 2 Calculation Based on Generation: All Remote All Local NACD In the short circuit option tab “Control for ANSI/IEEE” the user has selected the fixed MF factor NO Interrupting Duty YES YES NO Calculate: Total Remote Contribution Total Local contribution Total Contribution (Iint.peak*100/ device peak (crest) rating NO Yes Pass Fail Pass Fail Calculate 3 phase device duty using EQ-6a NO Fail Calculate %rating=Iint*100/ 3P device Int rating Figure 33: Device Evaluation.7 ALL Remote Calculate MFr using EQ-4 Iint=MFr*Iint.rms.asym? Yes Pass Calculate %rating=Imom.rms Calculate Imom.asym=MFm*Isym.sym) NACD using (EQ-3) If NACD=0 then all contribution are Local If NACD=1 then all contribution are Remote Peak Duty (Crest) Peak Duty (Crest) Momentary Duty (C&L) MFm = 1.rms rating . ANSI Standard.peak=MFp*Isym. are factors which might prove particularly critical. This contrary to the tendency for reducing protection times in modern equipment. but this presents obvious difficulties if varying design technologies have specific sensitivities. This progression is also perceived to have led to an inevitable reduction in inherent design margins such that much of the older equipment. then the greatest represents the maximum rated voltage. interpolation of test evidence is relatively simple and accepted. High Voltage Breakers. such interpolations are far more difficult to achieve simply and it is quite conceivable that critical fault duties may be identified at fractional short-circuit levels. the high energies and relatively low di/dt values associated with an asymmetrical duty make it less onerous for such a device than an equivalent symmetrical duty. 102 . although this does not alleviate the duty on other associated equipment and may be inconvenient from an overall system viewpoint. However. However. in technologies where the basic interruption characteristics of the device are duty dependent. may have considerable margins in hand-over and above modern equipment. but non-preferred.Short Circuit Analysis Program ANSI/IEC/IEEE 12. This trend is not problematic in itself but further emphasizes the need for future testing regimes to be fully representative of the system conditions in which the equipment needs to function correctly. solution to problems of asymmetric switching is to increase circuit-breaker operating times. Normally the interrupting current is a constant current at any voltage. Ultimately. a2) Rated insulation level.4. for which extensive operating experience is available. The standard values for the rated frequency of high voltage circuit-breakers are 50 Hz and 60 Hz. Low Voltage Breakers. In principle. equipment testing should consider the equipment under test to be a "black box" model regardless of the technology being employed. the effect of low energy minor loops and the possibility of extended arcing periods. in what are generally very short overall travel times. However. An obvious. reduced size. The same standards are used for LVPCB and MCCB.4. On the HV breakers it may to check if the breaker voltage rating is greater than the system voltage. It must be stressed at this point that there is no intention to cast doubt on the capabilities of particular equipment design philosophies merely to emphasize that as refined design techniques lead to minimized designs so the importance of well constructed and realistic testing regimes increases. The voltage rating of IEC breakers is the maximum voltage that the breaker can be applied at. a3) Rated frequency fr. energy requirements and cost.4 IEC Standard Based Device Evaluation (PDE IEC) 12.1 Circuit-Breakers Circuit-breaker design techniques have improved over time leading to benefits of technical performances. some manufacturers do give a different current at various voltages. 12.: If the manufacturer indicates a few values for the rated voltage. weight. In technologies where the interruption capability is fundamentally constant regardless of the switching duty.2 Rated characteristics to be given for all circuit-breakers a1) Rated voltage Ur. It is necessary that the last mentioned value to be lower than the product between the short duration acceptable rated current and the factor n. 103 . pt . I e 2. The rated short-time withstand current Icw of a CB. admited. Tcw 1s . a5) Rated short-time withstand current Icw. indicated in table 3.Short Circuit Analysis Program ANSI/IEC/IEEE a4) Rated normal current Ir: Current which the main circuit of a circuit-breaker is capable of carrying continuously under specified conditions of use and behavior. 89 A complete determination of the rated short-time withstand current is made. The rated short-time withstand current must be greater than twelve times the rated maximum operation current and. The testing determination of this current for a concret equipment is made in standard conditions CEI 60947-1. pt . the current duration must be 1 s: I cw 12 I e . 90 I cw 30 kA. I e 2. indicated by a manufacturer. 5 kA. the time constants and the ratio n between the peak value and the rated shorttime withstand current. 92 Values of the power factor.5 kA.5 kA . pt . which the equipment can support without any damages. 91 InAC the rated short-time withstand current is compearing with the rms value of the periodical short-circuit current component. as follows: I cw Max12 I e . in accordance with CEI 60947-1: I k n I cw . disconector or swich-disconector means the rms value of a rated. short-time current. without other manufacturer’s indication. on the base of the mentioned standard. 41 1. a10) Rated pressures of compressed gas supply and/or of hydraulic supply for operation. for which the following normalized values are recommended: 0. 4. 0. 6 (6.33] EN 60947-3:1999 Low-voltage switchgear and controlgear – Part 3: Switches. interruption and insulation.5. a7) Rated duration of a short-circuit tk. 3 (3.5.20 At the same time. switchdisconnectors and fuse-combination units.25. Direct over current releases include integrated tripping systems. This break time is that required by the circuit-breaker with the over current release set for the maximum time lag when operating in accordance with its rated operating sequence.1. 0.5 (4. 20 (20. disconnectors.25 0. kA ≤1.3 0.47 1. When connected in a circuit the prospective breaking current of which is equal to its rated short-circuit breaking current. 0.42 1.53 1.00 2. as applicable.1 s The rated short-time withstand current is equal to the rated short-circuit breaking current [5. 50 50≤ Power Factor 0.10 2.95 0.2 Time constant.70 2. a9) Rated supply frequency of closing and opening devices and of auxiliary circuits. ms 5 10 15 n factor 1. a8) Rated supply voltage of closing and opening devices and of auxiliary circuits Ua.5 0. 10 (10. 104 .05. a6) Rated peak withstand current (Ip): It is equal to the rated short-circuit making current.9 0. p.8 0. the short duration acceptable rated current represents the upper limit value of the rms value of the short-circuit current periodical component which is presumed constant during the short timing .Short Circuit Analysis Program ANSI/IEC/IEEE Table 9: n factor based on PF and short circuit level Short-circuit current. A rated duration of a short-circuit need not be assigned to a self-tripping circuit-breaker provided that the following applies. the circuit-breaker shall be capable of carrying the resulting current for the break-time required.7 0.5.5 (1. associated with it.15 – 4 – 5 – 6.Short Circuit Analysis Program ANSI/IEC/IEEE a11) Rated short-circuit breaking current Icn. which is expected by the manufacturer to cover the entire population of the circuit-breaker concerned under any operational conditions when breaking asymmetrical currents.for a self-tripping circuit-breaker. For three-pole circuit-breakers. The following applies to a standard circuit-breaker: . The minimum opening time mentioned above is that specified by the manufacturer. the AC component relates to a three-phases short-circuit.6 – 2 – 2.at voltages above the rated voltage. no short-circuit breaking current is guaranteed. Time Tr in the formula (6) is to be set to 0 ms .3 – 8} n and their products by 10 .at voltages below and equal to the rated voltage. % . it shall be capable of breaking its rated short-circuit breaking current . The rated short-circuit breaking current is characterized by two values: – the rms value of its AC component. the percentage DC component shall correspond to a time interval equal to the minimum opening time of the first opening pole Top of the circuit breaker. the rated short-circuit breaking current is characterized only by the rms value of its AC component. The R10 series comprises the numbers {1 – 1. the percentage DC component shall correspond to a time interval equal to the minimum opening time of the first opening pole Top of the circuit-breaker plus one half-cycle of rated frequency Tr. The value of the percentage DC component shall be determined as follows: . under the conditions mentioned above. any percentage DC component up to that specified. The percentage value of the dc component (iDC%) is based on the time interval (Top + Tr) and the time constant using the formula: Top Tr id . The circuit-breaker shall be capable of breaking any short-circuit current up to its rated short-circuit breaking current containing any AC component up to the rated value and.c.5 – 3. Such a current is found in a circuit having a power-frequency recovery voltage corresponding to the rated voltage of the circuitbreaker and having a transient recovery voltage equal to a specified value. The rated short-circuit breaking current is the highest short-circuit current which the circuit breaker shall be capable of breaking under the conditions of use and behavior prescribed in standards. The standard value of the AC component of the rated short-circuit breaking current shall be selected from the R10 series specified in IEC 60059.25 – 1. % 100 exp 105 . – the percentage DC component. The minimum opening time is the shortest opening time.for a circuit-breaker which is tripped solely by any form of auxiliary power. If the DC component does not exceed 20%. current component in relation to the time interval from initiation of short-circuit current. In addition. etc. In these circumstances. These special case time constant values recognize that the standard value may be inadequate in some systems.C. for different time constant. design of lines.120 ms for rated voltages up to and including 52 kV .75 ms for rated voltages 550 kV and above Figure 34: Percentage D. some applications may require even higher values.Short Circuit Analysis Program ANSI/IEC/IEEE The graphs of the DC component against time given in figure 1 below are based on: a) standard time constant of 45 ms b) special case time constants. 106 . the required DC component and any additional test requirements should be specified in the inquiry. related to the rated voltage of the circuit-breaker: .60 ms for rated voltages from 72. They are provided as unified values for such special system needs. for example their particular system structures.5 kV up to and including 420 kV . for example if a circuit-breaker is close to a generator. a12) Rated ultimate short-circuit breaking capacity Icu The rated ultimate short-circuit breaking capacity Icu represents the highest rms value of the current that the device is able to interrupt without suffering significant damages. taking into account the characteristics of the different ranges of rated voltage. This parameter is indicated by the equipment manufacturer in the device catalogue data. by multiplying it to the factor k. a14) The rated short-circuit making current Icm of a circuit-breaker having simultaneity of poles is that which corresponds to the rated voltage and the rated frequency. In some cases. and where the short-circuit currents are relatively large in relation to the maximum short-circuit current at the point under consideration. is used for testing at short-circuit breaking currents equal to the rated value. for LVCB. particularly in systems with a voltage less than 100 kV. The rated short-circuit making capacity Icm of a circuit-breaker or switch represents the value of the shortcircuit closing capacity. the transient recovery voltage approximates to a damped single frequency oscillation. In other cases. or in systems with a voltage greater than 100 kV in conditions where the short-circuit currents are relatively small in relation to the maximum short-circuit currents and fed through transformers. the transient recovery voltage contains first a period of high rate of rise. According to IEC 60947-1 the rated short-circuit making capacity is established in comparison with the limit value of the short-circuit rated breaking capacity Icu. This waveform is adequately represented by an envelope consisting of two line segments defined by means of two parameters. This is taken into account by introducing a time delay. in accordance with the relationship: I cm k I cu 94 107 . given in the table 2. determined under the conditions specified in the product standard. particularly in systems with a voltage 100 kV and above. is the upper (superior/higher) limit of the short-circuit ac component (the dc component is considered null): I cu I k 93 a13) Transient recovery voltage . This waveform is generally adequately represented by an envelope consisting of three line segments defined by means of four parameters. followed by a later period of lower rate of rise. expressed by the highest instantaneous value of the current that the device can connect at the rated voltage and frequency and at a specified power factor. The influence of local capacitance on the source side of the circuit-breaker produces a slower rate of rise of the voltage during the first few microseconds of the TRV.TRV related to the rated short-circuit breaking current is the reference voltage which constitutes the limit of the prospective transient recovery voltage of circuits which the circuit-breaker shall be capable of withstanding under fault conditions.Short Circuit Analysis Program ANSI/IEC/IEEE The magnitude of this current. The transient recovery voltage corresponding to the rated short-circuit breaking current when a terminal fault occurs. 50 50 cos k 0.opening time of a circuit-breaker defined according to the tripping method as stated below and with any time delay device forming an integral part of the circuit-breaker adjusted to its minimum setting 108 .25 0.20 1. kA (6.Short Circuit Analysis Program ANSI/IEC/IEEE Values of the multiplying factor k when fixing the rated short-circuit making capacity Icm of the LVCB Table 10: Icu and k factor Icu. a16) Rated time quantities: . for a rated frequency of 60 Hz and the standard value of the time constant of 45 ms it is equal to 2.0 2. In this case.6 times the rms value of the AC component of its rated short-circuit breaking current for all special case time constants it is equal to 2.5 times the rms value of the AC component of its rated short-circuit breaking current (Icn).50 0. 96 where the multiplying factor kH was introduced. 20 (20.7 2.7 times the rms value of the AC component of its rated short-circuit breaking current.2 The rated short-circuit making capacity implies that the breaker is able to connect the current suitable to this rated capacity at an applied voltage corresponding to the use rated voltage.30 0. the rated short-circuit making capacity Icm of an CB is compared with the peak current ip and the next inequality have to be fulfilled in order that the device withstands the short-circuit action: I cm i p 95 The following values apply for the high voltage CB (Ur >1 kV): for a rated frequency of 50 Hz and the standard value of the time constant of 45 ms it is equal to 2. so a following relationship can be written: I cm k H I cn . Being an instantaneous value. 10 (10. independent of the rated frequency of the circuit-breaker a15) Rated operating sequence.5.1 2. kH=2. Short Circuit Analysis Program ANSI/IEC/IEEE . Releases shall bear the appropriate data. the opening time is the interval of time between the instant at which.arcing time (of a multipole switching device): interval of time between the instant of the first initiation of an arc and the instant of final arc extinction in all poles . the circuit-breaker being in the closed position. and the instant when the arcing contacts have separated in all poles .for a circuit-breaker tripped by any form of auxiliary power. the circuit-breaker being in the closed position. the current in the main circuit reaches the operating value of the over current release and the instant when the arcing contacts have separated in all poles The opening time may vary with the breaking current. the opening time is the interval of time between the instant of energizing the opening release.4.break time: interval of time between the beginning of the opening time of a mechanical switching device and the end of the arcing time 12. the instant when the arcing contacts have separated in all poles is determined as the instant of contact separation in the first unit of the last pole.for a self-tripping circuit-breaker. The nameplate shall be visible in the position of normal service and installation. The main nameplate information is indicated in the Table 10 below. 109 . .3 Circuit Breaker Name Plate Data The nameplates of a CB and its operating devices shall be marked and must contain data in accordance with the standards IEC Standards. Table 11: CB Name plate data Information Abbreviation Unit Ur kV Up kV Us kV fr Hz Ir Isc A kA (idc%) % tk s Manufacturer Type designation and serial number Rated voltage Rated lightning impulse withstand voltage Rated switching impulse withstand voltage Rated frequency Rated normal current Rated short-circuit breaking current DC component of the rated short-circuit breaking current Rated duration of short-circuit Required marking condition Mandatory for CB and operation device “ Mandatory “ Rated voltage 300 kV and above Rating is not applicable at both 50 Hz and 60 Hz Mandatory “ More than 20 % Different from 1 s Coils of operating devices shall have a reference mark permitting the complete data to be obtained from the manufacturer. For circuit-breakers with more than one interrupting unit per pole. The opening time includes the operating time of any auxiliary equipment necessary to open the circuit breaker and forming an integral part of the circuitbreaker. and a slow-blow fuse may require twice its rated current for tens of seconds to blow. The speed at which a fuse blows depends on how much current flows through it and the material of which the fuse is made. At lower levels of distribution in an installation. Short-circuit currents initially contain DC components. characterized as "fast-blow".4. at lower distribution levels in an installation.4. Fuses have different characteristics of operating time compared to current. A standard fuse may require twice its rated current to open in one second. thereby minimizing danger and damage at the fault position. for AC). the DC transients (in this case) have an insignificant effect on the magnitude of the current peak.5 Fuse IEC Characteristic Quantities [IEC 60269-1] Prospective current (of a circuit with respect to a fuse) – current that would flow in the circuit if each pole of the fuse were replaced by a conductor of negligible impedance. The operating time is not a fixed interval. A characteristic of modern cartridge fuses is that. One of the most critical factors for optimum protection is proper fuse selection.g.4 FUSES The fuses can operate as single devices or can be combined with switch disconnectors. but decreases as the current increases.Short Circuit Analysis Program ANSI/IEC/IEEE 12. For AC.5 (standardized by IEC). 12. according to time required to respond to an over current condition. so that the fault current never reaches its prospective peak value [Schneider]. As already mentioned.41. a current cut-off begins before the occurrence of the first major peak. and fault levels are generally low. Fuse Breaking capacity – value of prospective current that a fuse is capable of breaking at a stated voltage under prescribed conditions of use and behavior (the rms value of the periodic component. R greatly predominates XL. This limitation of current reduces significantly the thermal and dynamic stresses which would otherwise occur. On the other hand. The choice depends on each application requirements and specific network conditions. the magnitude and duration of which depend on the XL/R ratio of the fault current loop. as previously noted. This can be done based on theoretical calculations but in many cases practical knowledge obtained from actual test results could make it easier and even more reliable. I t and cut-off current characteristics. the prospective current is expressed by the rms value of the AC component. Breaking range – range of prospective currents within which the breaking capacity of a fuse-link is assured. The peak-current-limitation effect occurs only when the prospective rms AC component of fault current attains a certain level. XL is small compared with R and so for final circuits Ipeak / Irms ~ 1. The rated short-circuit breaking current of the fuse is therefore based on the rms value of the AC component of the prospective fault current. can be as high as 2. a fast-blow fuse may require twice its rated current to blow in 0. owing to the rapidity of fusion in the case of high shortcircuit current levels. Note: the prospective current is the quantity to which the breaking capacity and characteristics of the fuse 2 are normally referred. No short-circuit current-making rating is assigned to fuses. Close to the source (MV/LV transformer) the relationship Ipeak / I rms (of AC component) immediately following the instant of fault. This means that the level of fault current may not attain values high enough to cause peak current limitation.1 seconds. Cut-off current – maximum instantaneous value reached by the current during the breaking operation of a fuse-link when it operates in such a manner as to prevent the current from reaching the otherwise attainable maximum. e. 110 . "slow-blow" or "time-delay". as previously mentioned. purposes the difference between pre-arcing and operating time is negligible.interval of time between the instant of the initiation of the arc in a fuse and the instant of final arc extinction in that fuse. Time-current characteristic – curve giving the time. let-through current characteristic – curve giving the cut-off current as a function of the prospective current under stated conditions of operation. Note: the peak withstands current is not less than the highest cut-off current of any fuse-link with which the fuse-holder is intended to be associated. melting time – interval of time between the beginning of a current large enough to cause a break in the fuse element(s) and the instant when an arc is initiated. under specified conditions. Note: in the case of AC. 2 I t zone – range contained by the minimum pre-arcing I2t characteristic and the maximum operating I2t characteristic. under specified conditions. 111 . Peak withstand current – value of the cut-off current that the fuse-holder can withstand. Arcing time of a fuse . Time-current zone – range contained by the minimum pre-arcing time-current characteristics and the maximum operating time-current characteristic. pre-arcing time or operating time as a function of the prospective current under stated conditions of operation.Short Circuit Analysis Program ANSI/IEC/IEEE Cut-off current characteristic. 2 I t (Joule integral) – integral of the square of the current over a given time interval: I 2t t 1 i 2 dt 0 t 97 Notes: 2 2 The pre-arcing I t is the I t integral extended over the pre-arcing time of the fuse 2 2 The operating I t is the I t integral extended over the operating time of the fuse The energy in Joules released in a 1Ω resistor in a circuit protected by a fuse is equal to the value of 2 2 the operating I t expressed in A s 2 I t characteristic – curve giving I2t values (pre-arcing I2t and/or operating I2t) as a function of prospective current under stated conditions of operation. Pre-arcing time. for practical. Conventional non-fusing current (Inf) – value of current specified as that which the fuse-link is capable of carrying for a specified time (conventional time) without melting. the values of the cut-off currents are the maximum values which can be reached whatever the degree of asymmetry. In the case of DC.g. Note: for times longer than 0. total clearing time – sum of the pre-arcing time and the arcing time. e.1 s. Rated current of a fuse-link (In) – value of current that the fuse-link can carry continuously without deterioration under specified conditions. the values of the cut-off currents are the maximum values reached related to the time constants as specified. Operating time. 4. 5. 6.Short Circuit Analysis Program ANSI/IEC/IEEE Conventional fusing current (If) .value of current specified as that which causes operation of the fuse-link within a specified time (conventional time). 3.4.6 Fuse nameplate data The follwoing data will generally be provided for a fuse: 1. fuse speed Approvals by national and international standards agencies Manufacturer / part number / series Breaking capacity 112 . 12.e. 2. i. Rated current (Ampere rating) of the fuse Voltage rating of the fuse Time-current characteristic. 5 Protective Device Evaluation Based on IEC Standard Figure 35: IEC PDE Flow Chart – Part 1 113 .Short Circuit Analysis Program ANSI/IEC/IEEE 12. Short Circuit Analysis Program ANSI/IEC/IEEE b Figure 36: IEC PDE Flow Chart – Part 2 114 . Short Circuit Analysis Program ANSI/IEC/IEEE c Figure 37: IEC PDE Flow Chart – Part 3 115 . Compare Icm with the peak short-circuit current. if Ur > Un then the real breaking capacity of the fuse will be used in the next steps. For the PASS situation Top Tr Calculate i dc % exp . if Ur = Un then the fuse breaking capacity rating (Irb) = the fuse real breaking capacity (Ib). otherwise Fail.a. Determination of the LVCB short-circuit making current Icm. for this situation calculate the fuse real breaking capacity: Ib Ur I rb . For both situations of the last comparison Calculate %rating I"k Ib 12. otherwise Fail. 116 . Un Compare the fuse real breaking capacity against the initial symmetrical short-circuit current I k" : " if Ib ≥ I k then the device Pass.5.5. b. if Icm ≥ ip then the device Pass. For the Ur ≥ Un case.2 LVCB Evaluation The LVCB evaluation begins after the comparison of the CB rated voltage presented in the right side of the figure 2.1 Fuses Evaluation Compare the voltage rating of the fuse (Ur) against the system voltage (Un) where the fuse is placed: if the fuse rated voltage Ur ≥ Un then the device Pass. otherwise Fail (the user have to verify the fuse ratings). there are two situations: a.Short Circuit Analysis Program ANSI/IEC/IEEE 12. For the FAIL situation Calculate % rating ip I cm 100 . 117 . 12. 100 Compare the asymmetrical short-circuit presumed current with the CB short-circuit breaking current Icn.Short Circuit Analysis Program ANSI/IEC/IEEE Where: Top represents the minimum opening time and it is specified by the manufacturer. For both situations of the last comparison calculate % rating I asymsc I cn 100 . τ – circuit time constant. presented in Figure 2.5. if Iasymsc < Icn then the LVCB Pass. 2 Calculate the asymmetrical short-circuit presumed current I asymsc I k i % 1 dc . otherwise Fail.b. Tr – according to the specifications from figure 2.c is similar to the LVCB one. according to the IEC standards calculus. given in paragraph. The differences occur just in the loop of the Icm determination.3 HVCB Evaluation The HVCB evaluation. 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