39644125 Module 1 Medium Voltage Switchgear Assemblies

SUBSTATION COMMISSIONING COURSEPage 1 of 46 SUBSTATION COMMISSIONING COURSE MODULE ONE MEDIUM VOLTAGE SWITCHGEAR ASSEMBLIES Written by: Raymond Lee, Technical trainer Copyright ©2010 Electrical Industry Training Centre of Alberta 4234 – 93 Street Edmonton, Alberta, Canada Phone: (780) 462-5729 Fax: (780) 437-0248 Page 1 of 46 SUBSTATION COMMISSIONING COURSE Page 2 of 46 TABLE OF CONTENTS Headings Page Page 2 of 46 SUBSTATION COMMISSIONING COURSE Page 3 of 46 Introduction: Module One explains the construction aspects of the Medium Voltage (MV) switchgear assemblies from its physical attributes to the various compartmentalized functional sections By the end of this module, the participants should be knowledgeable in the construction aspects of the MV switchgear and be able to identify its major and basic parts. This knowledge will prepare the participants to work comfortably around the switchgear when performing commissioning tests. Page 3 of 46 SUBSTATION COMMISSIONING COURSE Page 4 of 46 1. Switchgear Standards Switchgear and control panels are found in power generating stations, distribution substations, commercial and institutional buildings, industrial plants, factories, paper mills and other facilities where electric energy is utilized or electric power is distributed. The major North American standards that govern the design, manufacture and testing of the medium voltage switchgear assemblies are CSA, ANSI/IEEE, IEC, EEMAC and NEMA. • CSA - Canadian Standards Association (1919) • ANSI - American National Standards Institute (1989) • IEEE - Institute of Electrical and Electronics Engineers (1963) • EEMAC - Electrical Equipment Manufacturers Association of Canada (1976) • NEMA - National Electrical Manufacturers Association (1926) • CEMA – Canadian Electrical Manufacturers Association (1944), became EEMAC with the merger of Electronic Association of Canada which developed out of the Radio Manufacturers Association of Canada (1929) 1.1Canadian Standards Canada has two electrical standards, Canadian Standards Association (CSA) and Electrical and Electronic Manufacturers Association of Canada (EEMAC). 1.1.1 CSA Standards Canadian Standards Association (CSA) Standard C22.2 No 31- 10 covers deadfront indoor enclosed and outdoor enclosed assemblies of switchgear devices, such as: • Switches • Interrupting devices • Air circuit breakers • Power circuit breakers • Control, metering, protective and regulating equipment with associated interconnections and supporting structures. Page 4 of 46 UL-C labels are affixed to equipment produced in the US that complies with the Underwriter Laboratories product safety certification program but tested to CSA standards. definitions and testing procedures. Equipment installed which does not bear the CSA or UL-C label are subjected to a special inspection by the Canadian inspection authorities for use in Canada and if approved.1. Current EEMAC Standard that are referenced in CSA standards are: • EEMAC G8-3. CEMA sister organization in the US is NEMA and comparable standards in Canada are the CEMA standards. EEMAC standards have referenced many of the applicable ANSI / IEEE standards for ratings. The components that are used to build the equipment must comply with the applicable requirements of the Canadian Electrical Code that governs such components. CSA approval Metal-clad switchgear approved for use in Canada will bear the CSA label.2 EEMAC and CEMA Standards CSA Standards references EEMAC standards within its writings which is the Electrical and Electronic Manufacturers Association of Canada standards.2 No 31-10 covers the construction and design features required for equipment with nominal voltage of 46kV or less.2. CSA labels are affixed by the manufacturers that have passed the CSA’s approval for their manufacturing process. a number of them continue to be referenced in CSA standards. 1. and are subject to ongoing regular inspection to be in compliance with the requirements of the applicable CSA standards. will be affixed by a special inspection sticker. Switchgear with UL-C labels are accepted by the Canadian inspection authorities. In turn. 1989.SUBSTATION COMMISSIONING COURSE Page 5 of 46 CSA Standard C22. While most EEMAC Standards are inactive and out of date. Standard for Metal-Clad and Station-Type Cubicle Switchgear Page 5 of 46 . EEMAC has not supported the development or updating of any EEMAC Industry Product Standards since 1994. 1972. • EEMAC G14-1. Year later AIEE merged with IRE to form IEEE and the AIEE Standard 27 became the IEEE 27.IEEE Standard for Indoor AC Switches (1kV – 38 kV) Page 6 of 46 .20. After World War II.20. These include: • low voltage power circuit breaker switchgear to 600 Vac • medium voltage metal-clad switchgear above 1000v up to 38k Vac • metal enclosed load interrupter switchgear above 1000v up to 38k Vac.20 covered switchgear assemblies across the voltage spectrum. is a membership organization that coordinates the development of US voluntary standards in both the private and public sector. Note: American National Standard Institute (ANSI).20. the various standard organization worked together to consolidate the standards requirements. In 1987 C37.IEEE Standard for Metal-Enclosed Interrupter Switchgear • C37.20 of today.IEEE Standard for Metal-Clad Switchgear • C37.SUBSTATION COMMISSIONING COURSE Page 6 of 46 • EEMAC G11-1.3 . • C37.2 American Switchgear Standards The evolution of the standards originated with the first written standard by The Electric Power Club which today became NEMA. which formed the basis for ANSI/IEEE C37. It is the US member body to ISO and IEC C37. NEMA was a merger between the Associated Manufacturers of Electric Supplies and The Electric Power Club.20 was revised into separate standards to produce 1 document for each major equipment classes. Guide for Measurement of Corona in Switchgear Assemblies.IEEE Standard for Metal-Enclosed Low-Voltage Power Circuit Breaker Switchgear • C37.2 . The resulting work culminated to form AIEE Standard 27.4 . 1987. The American Institute of Electrical Engineers (AIEE) was in existence at the time and they also worked on their own switchgear standards. Procedure for Testing The Resistance of Metalclad Switchgear Under Conditions of Arcing Due To Internal Fault 1.20.1 . September 1926. 2. C37. A special inspection sticker is still required for approval by the electrical inspection authority.010. IEC standards are synonymous with International standards. The more significant standards for switchgear are the switchgear standard C37.04. Page 7 of 46 . The standards listed is not all inclusive.20. IEC was founded in 1906. 1.09 and C37.06. IEC Standard 62271-200 ‘AC metal-enclosed switchgear and controlgear for rated voltage above 1kV and up to and including 52kV’ is the comparable to the ANSI / IEEE Standard C37.2 and the breaker standards C37. are quite different from what is expected of switchgear designed and tested to the North American Standards.3 International Standards The International Electrotechnical Commission (IEC) is the international standards and conformity assessment body for all fields of electrotechnology. IEC Standard related to metalclad switchgear. Ratings and test results are also different. C37. wires and other equipment or devices within the switchgear assemblies.SUBSTATION COMMISSIONING COURSE Page 7 of 46 for Use in Metal Enclosed Switchgear Table 1 lists the principle standards that are applicable to Medium Voltage Metal-Clad Switchgear of today.20. device numbers. It is beyond the scope of this module to discuss the difference and similarities of these two standards. There are other standards that are applicable to relays. but it is notable to say that the IEC designed switchgears can be in compliance to the requirements of the CSA standards. based in Geneva and is made up of national committees from over 60 countries. 2 G11-1 G14-1 2010 1989 1983 2009 1989 1972 1987 ANSI / NEMA ANSI / NEMA CSA CSA CSA CSA EEMAC EEMAC EEMAC Standard Rating Structure for AC HV Circuit Breakers Standard for AC HV Circuit Breakers Rated on a Symmetrical Current Basis – Preferred Ratings and Related Required Capabilities for voltages above 1000 V Test Procedure for AC HV Circuit Breakers Application Guide for AC HV Circuit Breakers Rated on a Symmetrical Current Basis Metal-Clad and Station-Type Cubicle Switchgear Standard for 4.2 # 31 C22.04 C37.55 2002 C37.2 1999 C37.2 # 193 C22.2 # 253 G8-3.6 2007 IEEE ANSI / IEEE ANSI / IEEE IEEE C37.010 1999 1999 C37.SUBSTATION COMMISSIONING COURSE Page 8 of 46 TABLE 1: NORTH AMERICAN SWITCHGEAR STANDARDS SPONSOR TITLE STANDARD REV C37.76 TO 38 Kv Rated Grounding and Test Devices Used in Enclosures Conformance Test Procedures for Indoor Alternating-Current MV Circuit Breakers Applied as Removable Elements in Metal Enclosed Switchgear Assemblies Metal-Clad Switchgear Assemblies – Conformance Test Procedures Switchgear .85 2002 C22.54 2002 ANSI / NEMA C37.2 # 58 C22.Alternating-Current High Voltage Power Vacuum Interrupters – Safety Requirements for X-Radiation Limits Switchgear Assemblies HV Isolating Switches HV Full-Load Interrupter Switches MV AC Contactors. Controllers and Control Centres Standard for Metal-Clad and Station-Type Cubicle Switchgear Guide for Measurement of Corona in Switchgear Assemblies Procedure for Testing The Resistance of Metalclad Switchgear Under Conditions of Arcing Due To Internal Fault WORKING GROUP IEEE NEMA IEEE IEEE IEEE IEEE NEMA NEMA NEMA CSA CSA CSA CSA Page 8 of 46 .06 1999 2009 IEEE IEEE C37.09 C37.20.20. ac assumed). CSA standard C22. power circuit breakers along with control. along with control. Local breaker control can be performed via with door mounted push buttons. they can be fitted with a electrical operator when required.2 Major Parts The major parts of the switchgear are provided within its definition.1 Control devices: Control devices provide local and / or remote control to operate the main switching or interrupting devices. MV Switchgear Definition: A MV switchgear are compartmentalized assemblies of switching and interrupting devices operating from 1000V to 38 kV supplied from an insulated main bus structure. air circuit breakers.2. 2.1 What is a Medium Voltage Switchgear? When we say “medium voltage.SUBSTATION COMMISSIONING COURSE Page 9 of 46 2.2 No 31-10 applies to deadfront indoor enclosed and outdoor enclosed assemblies of switchgear devices such as switches and interrupting devices. Page 9 of 46 . protective and regulating equipment with associated interconnections and supporting structure. metering. protective and regulating equipment with associated interconnections and supporting structure. Load-break disconnects are normally operated by a manual operating handle. Switchgear and Switchgear Assemblies 2.” we are referring to a range of voltage from 1000 volts to 38 kV (as per ANSI / IEEE 1585 – 2002. metering. They are listed as: • Control devices • Switching and Interrupting devices • Metering devices • Protective devices • Regulating devices • Interconnections • Supporting structure 2. pistol grip breaker control switch or local centralized breaker control panel. Load break switches / disconnects are designed to interrupt normal load current. Control devices are: • Local controls devices • Remote controls devices 2. Load break switches / disconnects are able to make short circuit currents for inadvertent situations when they are closed onto a faulted condition. No-load / isolating disconnects are used for no-load operation. load interruptors / disconnectors • No-load / isolating disconnects Page 10 of 46 . It main function is to provide a visible break and a lockable point for isolation purposes for maintenance / repair of downstream equipment. For those scenarios when load break switches are closed onto a fault. they are not designed to interrupt fault current.2 Switching and Interrupting Devices: Switching and Interrupting devices are installed in the primary circuit to control the flow electrical energy. the upstream protective device shall operate to interrupts the short circuit currents and isolate the faulted part of the power system. The rating of the switching or interrupting devices will determine if the device is able to make or break load current. They are fitted with a fast acting make / break mechanism and arc quenching devices.SUBSTATION COMMISSIONING COURSE Page 10 of 46 Remote operations can be initiated via SCADA or other communication equipment using interface / interposing relays or through a remote terminal unit (RTU) that sends control signals in parallels with the local controls.2. Switching and Interrupting devices are: • Circuit breakers • Load-break switches / disconnect. overload current or short-circuit current. Examples of abnormal operating conditions are: • Under-voltage / over-voltage • Under-frequency / over-frequency • Under-speed / over-speed • High temperature • High vibration • Reverse power • Overload • Short-circuit Some protective devices are: • Fuses • Overload relays • Temperature relays • Protective relays Page 11 of 46 . • Instrument transformers: Current transformers (CT). Amp. protective devices may trip the supply breaker to isolate the faulted part of the power system or initiate an alarm to signal the operator to take corrective action. frequency and phasing through the use of instrument transformers which convert and isolate the primary quantities into useable low voltage secondary quantities. Ammeter. Var.4 Protective Devices: Protective devices monitor the system’s operating parameters for abnormal operating conditions. Synchroscope (120V.SUBSTATION COMMISSIONING COURSE Page 11 of 46 2. Metering devices enables the operators to quantify the operating conditions of the system. Power Factor.2. Frequency. Depending on its function. Temperature • Revenue Meters: Watt-hour meter and Var-hour meter 2. Frequency.3 Metering devices Metering devices monitors the system parameters such as voltage. current.Watt.2. potential transformer (PT) • Switchboard instruments: Voltmeter. Var. Current Demand. Voltage transformer (VT). Watt. 5A) • Transducers: Volt. Capacitor banks are used to reduce the current demand during heavy load periods and / or reduce the voltage drop.SUBSTATION COMMISSIONING COURSE Page 12 of 46 2.6 Interconnections: Interconnection relates to the primary bus-bars connections between switchgear cubicles or between switchgear sections via enclosed bus structures / bus ways / ducts. The fan will stop if the load current drops below the setpoint value after a set time delay. 2. The general requirements as per ANSI. frequency. although it may vary for different classes of equipment.5 Regulating Devices: Regulating devices are used to control the operating parameters of the power system such as voltage. IEEE and NEMA standards for switchgear is a temperature rise of no more the 65°C. power. temperature and loading for machines. current. These devices are commonly associated with power generating equipment and become an integral part of the control systems. speed.2. Forced air-cooled circuit breakers employed a current sensing relay which initiate beaker cooling using fans when the load current approach 90-95% of the breaker continuous current rating. under-voltage sensing or both to control the application of capacitors by vacuum contactors. The requirement is to prevent overheating of the insulators and insulation support systems enclosing the bus bars since high temperature will reduce the life of the insulation. The efficiency of all types of heavy current busbars depends upon careful design. Regulating devices in switchgear are associated with forced air-cooled breakers and with metal enclosed capacitor banks. Temperature rise is the main design criteria used for establishing the continuous current rating for busbar design.2. tie lines or other apparatus. Factors affecting bus-bars temperature rise and bus bar design are: • Size and type of materials used (copper or aluminum alloys) • Insulated of un-insulated bars (insulated bars runs cooler from increased heat radiation due to darker color) • Maximizing the surface area for heat dissipation • Size and material of the enclosure around the bus • Air flow around the bus and enclosure • Not impeding the natural air currents due to busbars placement Page 12 of 46 . The control scheme for capacitor banks can utilize the reactive energy sensing. hot metal and gases away from the operator’s working area.SUBSTATION COMMISSIONING COURSE Page 13 of 46 • Achieving uniform current densities in all parts of the conductor • Minimizing skin effects and proximity effects for busbars Due to the complex interactions of the above and other factors. Insulators are integral to the design of the supporting structures which supports the busbars. • Insulated Main Bus and Connections All main bus and connections are insulated in a medium voltage metal-clad switchgear assembly. 2. The construction of the enclosures must be strong and rigid to withstand the operating mechanical forces of the equipment it supports / houses and withstand the magnetic forces that are produced from the flow of short circuit currents. Such features are standard for nuclear installations. Page 13 of 46 . This is not necessarily the case with other types of assemblies such as a panelboards.7 Supporting Structures: Supporting structure are the physical attributes of the switchgear enclosure. Arc resistant switchgear are designed to resist the explosive forces generated during an arc flash through the use of pressure relief vents to direct the rapidly expanding air.2. Seimic rated gear is another design feature to consider for installations in earthquake prone regions. continuous current tests are required as part of the standard to determine the temperature rise of a bus system design. where the main bus is not separated with the branch breaker distribution system. SUBSTATION COMMISSIONING COURSE Page 14 of 46 Switchgear examples: Switchgear brings a number of very important functions together in one package. Typical Medium Voltage Switchgear Assembly. Consisting of 5 Vertical Structures Figure 2. Figure 1. Typical 3 Vertical Structure Assembly with Upper Compartment Vacuum Circuit Breaker Removed from its Compartment on Extension Rails Page 14 of 46 . Higher ratings are available when fans are used to force-cool the equipment. they are: • 5 kV • 15 kV • 27 kV • 38 kV Current rating The main bus continuous current rating is a function of the protective device protecting the main bus.3. The current ratings are determined by the system requirements and the circuit breakers selected to provide the protection.SUBSTATION COMMISSIONING COURSE Page 15 of 46 2. 2000 or 3000 amperes.1 Electrical Voltage Category Medium voltage switchgear assemblies generally fall into one of four voltage category.3 Characteristics 2. 2000 or 3000 amp. Not all voltage levels offer the same continuous current ratings. control equipment compartments and other compartments for auxiliary equipment (such as VTs) • Insulated main bus and connections • Metal barriers separating each vertical structure and each compartment within each structure Page 15 of 46 . Frame sizes for circuit breakers are 1200. making the continuous current rating of the bus rated at 1200. Mechanical Aspects A typical medium voltage metal clad switchgear assembly has: • Removable / Draw-out circuit breakers • Main bus compartment • Incoming / outgoing compartments for line / cable connections • Circuit breakers. EEMAC G8-3-2 for Metalclad Structural Attributes Front and rear access (optional) Must have front and rear access Shutters not required Shutters required Comparmentalization not required All live parts are compartmentalized Adjacent compartments can be open Adjacent compartments are isolated Bus and primaries can be uninsulated Bus and primaries must be insulated Switching devices can be fixed mounted Switching devices must be draw-out Interrupting dev. Medium voltage switchgear assemblies are metal-clad. Metal Enclosed Metalclad Applicable Standards ANSI C37.2 for Breakers ANSI C37.2 # 31 includes Metalclad. However. but metal enclosed is not metalclad Page 16 of 46 .20. must be draw-out Overcurrent Protection Device Types Switches with or without fuses (typ) Vacuum circuit breakers with O/C PN.2 for Breakers ANSI C37. Metal enclosed assembly often associated with low voltage equipment encloses the equipment in metal vertical structures.2 # 31 for Switchgear Assy.3 for Switchgear CSA C22.20.3 Metal-Clad Vs Metal-Enclosed Medium voltage metal-clad switchgear has the structures and compartments within each structure physically separated from each other by grounded metal barriers.SUBSTATION COMMISSIONING COURSE Page 16 of 46 2. compartments are not separated from one another with metal barriers. CSA C22. Can be fixed mounted Interrupting dev. Overcurrent Protection Device Features Switches have low duty cycle Breakers have high duty cycle Metalclad is metal enclosed.20.3. C and D are performing other functions. Application Example The substation transformer steps the voltage down from 35 kV to 15 kV.SUBSTATION COMMISSIONING COURSE Page 17 of 46 Application Example Figure 3. It feeds a 15 kV medium voltage circuit breaker A. This is the main / incoming breaker of the medium voltage switchgear assembly Three other medium voltage circuit breakers B. Page 17 of 46 . Breaker B and C are feeder breakers and breaker C is the transformer breaker. Vertical structures are all bolted together to form one rigid. That could be one structure or many structures.1 Vertical Structure Width dimensions are usually 26.4. Access from the rear is provided through bolted. continuous assembly. 36 or 42 inches. Typical Medium Voltage Switchgear Assembly with One Circuit Breaker Compartment Door Open Page 18 of 46 . 2. or hinged doors. The front structures are normally hinged metal doors. and height of 90 to 100 inches. The exact dimensions of the vertical structure are dictated by the voltage class and specification requirements. Figure 4. 2. removable metal panels. 5 kV fussed motor starter and a 5 kV motor load.4 Basic Parts A switchgear assembly consists of as many vertical structures / sections required for the intended application.SUBSTATION COMMISSIONING COURSE Page 18 of 46 The rest of the system comprised of a 5 kV isolating switch. 4. with Several Rear Covers Removed 2. Compartment types are: • Circuit Breaker Compartment (A) • Main Bus Compartment (B) • Cable Connection / Line Compartment © • Low Voltage / Control Compartment (D) • Potential Transformer / Auxiliary Compartment (E) Page 19 of 46 .2 Compartments A medium voltage switchgear assembly is an integrated combination of a number of compartments. Page 19 of 46 Typical Medium Voltage Switchgear Assembly Rear View.SUBSTATION COMMISSIONING COURSE Figure 5. within which it performs its function. The circuit breaker compartment provides: • an enclosure for one circuit breaker • a means to physically move the circuit breaker into or out of the compartment between connected and disconnected position • a means to make primary electrical connections.4. prevents insertion of a closed breaker and prevent breaker operation until fully inserted. an upper VT compartment and a rear bus bar compartment. 2. Figure 6 shows a lower breaker compartment. Page 20 of 46 Sectional view of a Structure. self aligning and self coupling • disconnectable secondary control wiring connections • interlock to prevent insertion into the wrong compartment. Compartments and vertical structures are physically separated from one another by metal barriers. Each circuit breaker is provided with its own compartment.1 Circuit Breaker Compartment The removable draw-out circuit breaker is the heart of the switchgear.2. • extension rails to support the circuit breaker as it is pulled out of the compartment Page 20 of 46 .SUBSTATION COMMISSIONING COURSE Figure 6. Figure 7. Phase-B and Phase-C line and load side connections. Note: Do not move or handle the circuit breaker by the primary connecting device as damage may occur. Primary Electrical Connections Circuit breakers have six primary electrical connecting devices. and rear portions of the compartment. the faceplate of the circuit breaker itself acts as the front part of the compartment. Page 21 of 46 . They are arranged two per phase. When the circuit breaker is racked into its connected position. Breaker to primary bus connections is made via spring pressured contact finger clusters. bottom. Phase-A. Circuit Breaker Shown Being Manually Levered into Connected Position In this position. Each primary connecting device has multiple contact fingers which will mate with the bus bar stationary primary connecting stabs. the operating and current-carrying parts of the circuit breaker are compartmentalized from the rest of the assembly structure. Connections are automatically made as the circuit breaker is racked into position within the circuit breaker compartment and automatically disconnected as the breaker is racked out of the compartment. right and left sides.SUBSTATION COMMISSIONING COURSE Page 21 of 46 Enclosure The circuit breaker compartment includes a top. Control power is provided to the charging motor and other auxiliary devices through the plug connections. Showing Six Primary Finger Clusters When the circuit breaker is racked out of the connected position. The secondary contact plugs can be manually engaged when the circuit breaker is in the TEST position within its compartment (Figure 10). Page 22 of 46 .SUBSTATION COMMISSIONING COURSE Figure 8. Conversely the shutters move out of the way during breaker insertion for connection to the primary circuit. Once the plugs are connected. This safety device is called the automatic shutter system. Page 22 of 46 Rear View of Circuit Breaker. secondary male and female contact plug engages. the circuit breaker can be electrically operated while disconnected from the primary circuit. Secondary Electrical Connections When the circuit breaker is racked into the connected position. the rear bus connection points are covered via a closing shutter to prevent contact with the live primary circuit. When the circuit breaker is racked out of the connected position to the disconnected position. the secondary contacts plug disengages. SUBSTATION COMMISSIONING COURSE Figure 9. Page 23 of 46 Secondary Contacts Being Manually Engaged with Circuit Breaker in Test Position The secondary plug is often mounted on the underside of the circuit breaker. with the compartment’s secondary plug mounted on the compartment floor. Figure 10. Secondary Control Plug Shown Mounted on Floor of Circuit Breaker Compartment Page 23 of 46 . Safety interlocks in the compartment interact with matching circuit breaker interlocks. and must be supplied by all manufacturers.SUBSTATION COMMISSIONING COURSE Page 24 of 46 Safety Interlocks Safety interlocks are required by governing standards. The purpose of these interlocks is to ensure: • The circuit breaker cannot be removed from the test/disconnected to the connected position unless the main contacts are opened and secondary electrical connections are engaged • The circuit breaker cannot be removed from the connected to the test/disconnected position unless the main contacts are opened and secondary electrical connections are engaged • The secondary electrical connection cannot be broken when the circuit breaker is in the connected position • The circuit breaker cannot be removed from the compartment with the main contact closed or with the closing spring charged • Incorrect circuit breaker types are prevented from being inserted into the wrong circuit breaker compartment Extension Rails Extension rails provide equipment support and permit circuit breakers and other auxiliary devices such as large removable transformers to be withdrawn from the compartment for inspection and maintenance. There are both electrical and mechanical interlocks. Page 24 of 46 . 4.2 Main Bus Compartment The main bus comprised of a set of bus bars. The bushings are made of an insulating material. Page 25 of 46 Vacuum Circuit Breaker Withdrawn from Compartment on Extension Rails 2.2.SUBSTATION COMMISSIONING COURSE Figure 11. They typically copper of aluminum bus bars mounted on bushing. Two vacuum circuit breakers have been permitted to be installed in one vertical structure since the arcing current during contact part is contained within the vacuum bottles. Page 25 of 46 . SUBSTATION COMMISSIONING COURSE Figure 12. Page 26 of 46 . Bus connections between compartments must be insulated. Page 26 of 46 Two Vacuum Breakers In One Vertical Structure (Side View) Connections to the main bus within a vertical structure for circuit breakers and other devices are called Bus Joints. Three Main Bus Bars Extending Through Insulated Openings in the Side of Vertical Structure. Figure 13. the rated continuous current of the main bus is usually 1200. Isolating barriers are used within each vertical structure to compartmentalize the main bus from other compartments and equipment. In medium voltage switchgear assemblies. while maintaining the rated temperature requirements established by standards. Figure 14. Access to the main bus is provided by removing specific barriers. main bus bars are not usually one continuous piece or standard lengths bolted together. Page 27 of 46 . The bus system must be supported and braced to withstand the stresses created by short circuit currents. Rear View of Partial Assembly with Barriers Removed to Show Insulated Main Bus Bars Main bus conductors are sized to handle the current. To minimize occurrence of faults. buses are insulated with fluidized bonded epoxy insulation and bolted joints are covered with insulating boots. although higher ratings are possible using forced air cooling consisting of fans controlled via thermostats.SUBSTATION COMMISSIONING COURSE Page 27 of 46 Main Bus The main bus extends the length of the assembly from one vertical structure to another through insulated openings in the sides of the vertical structures. 2000 or 3000 amperes. Depending upon the length of the assembly. can also be mounted in the line compartment. Assembly designs permit entry and exit from the top or bottom. Figure 15. It is accessible via removable bolted rear panels or rear doors.2. The line compartment usually runs from top to bottom. Surge arresters and large control power transformers.SUBSTATION COMMISSIONING COURSE Page 28 of 46 2.4.3 Line Compartment The rearmost compartment is the line compartment. Space is provided in the compartment for incoming cable connections or other connecting means. Two Vertical Structures of One-High Circuit Breaker Switchgear.Rear Panels Removed (Rear View) Page 28 of 46 . Instruments.4. The rear portion of door-mounted devices protrudes into the compartment space. relays and other control equipment can be mounted on the rear door panel. Showing How Cable for Top Compartment Gets Through Bottom Compartment (Rear View).SUBSTATION COMMISSIONING COURSE Figure 16. control switches and other devices can be mounted in the door panel. Ground Bus An un-insulated ground bus runs the length of the assembly. Page 29 of 46 One Vertical Structure of Two-High Circuit Breakers.4 Control Compartment The control compartment is considered to be the space between the front of the circuit breaker face plate and the front door. it can alternatively be mounted in a dedicated auxiliary compartment. meters. Page 29 of 46 .2. indications. The ground bus is capable of carrying the rated short circuit current of the system. 2. If there is to be a large volume of control equipment. Relays. and is normally located in the lower part of the line compartment. 4.SUBSTATION COMMISSIONING COURSE Figure 17. Auxiliary Compartment Transformer Mounting Page 30 of 46 . An auxiliary compartment could be an entire full-height vertical structure.5 Auxiliary compartment Auxiliary compartment is usually located above or below a circuit breaker compartment.2. Page 30 of 46 Typical Circuit Breaker Compartment. Figure 18. Auxiliary compartments are frequently used to mount draw-out voltage transformers and large power control transformer. with Door-Mounted Devices Protruding Through Door 2. 5 Installations The two main installation types are: • Indoor • Outdoor Sub-classifications are based on enclosure types are: • NEMA 1 non-gasketed • NEMA 1A gasketed • NEMA 2 drip-proof • NEMA 12 dust-tight • NEMA 3R non-walk-in • NEMA 3R walk-in • and others Other sub-classification based of functionality are: • Sprinkler proof • Arc resistant • Dust proof • Seismic rated • Weatherproof Page 31 of 46 .SUBSTATION COMMISSIONING COURSE Figure 19. Page 31 of 46 Entire Vertical Structure Dedicated to Auxiliary Equipment 2. Longer life can be achieve if the environment within the enclosure can be controlled to mimicked an indoor environment.2 Outdoor Installation Outdoor switchgear incorporates and outdoor approved structure with an indoor switchgear components.5. Three primary outdoor installations are: • Aisle-Less switchgear • Sheltered Aisle Switchgear • Common Aisle Switchgear Page 32 of 46 . humidity and other environmental factors and still meeting design requirement.5. Not all manufacture will come up with the same configuration. 2. Figure 20.1 Indoor Installation All medium voltage switchgear assemblies start out as indoor assemblies.SUBSTATION COMMISSIONING COURSE Page 32 of 46 Switchgear assemblies are installed in a wide variety of locations under a wide range of climatic conditions. Typical Two-High Configurations 2. Configurations are designed to use the smallest amount of floor space and materials taking into account such factors as temperature. Page 33 of 46 . Weatherproof gasketed doors are normally at both end of the enclosure. Weatherproof gasketed sealed doors are located on the front to allow for the drawout and removal of the circuit breakers. Additional provision of added ventilation with space heater aids in minimizing condensation of moisture.SUBSTATION COMMISSIONING COURSE Page 33 of 46 Aisle-Less Switchgear Aisle-Less Switchgear are house in a weatherproof enclosure around an indoor switchgear assembly. Figure 26. An aisle is constructed as part of the enclosure at the front of the assembly. Removable weatherproof gasket panels or doors are provided for rear access. Typical Outdoor Aisle-Less Construction (Side View) Sheltered Aisle Switchgear An outdoor enclosure is constructed around an indoor switchgear assembly. Typical Outdoor Common Aisle Construction (Side View) Page 34 of 46 .SUBSTATION COMMISSIONING COURSE Figure 27. Figure 28. Page 34 of 46 Typical Outdoor Sheltered Aisle Construction (Side View) Common Aisle Switchgear This is a large assembly and installed in two parts on both sides of the aisle. The design of arc-resistant equipment is dedicated to the safe control and release of arcrelated overpressures. an assembly may frequently be required to meet specific local standards. A medium voltage switchgear assembly is built and tested in accordance with a specific set of engineering standards. Dominant Regional Standards Throughout the World In addition to regional standards. This is quite a task.SUBSTATION COMMISSIONING COURSE Page 35 of 46 3 Testing The design and proof testing and the production testing of a medium voltage switchgear assembly varies. IEEE. Depending of the geographical location some of the applicable standards may be ANSI. NEMA. Page 35 of 46 . considering the vast number of different devices and pieces that make up an assembly. Two such applications are seismically-qualified and arc-resistant equipment. depending upon whether it is compliant with ANSI or IEC standards. Very specific tests could even be required for the equipment before it can be permitted for use in certain areas or applications. the manufacturer must know and be able to prove by testing that each and every component functions properly when installed in the assembly. Unlike an individual component. CSA or EEMAC. which also must meet certain specific standards. Figure 29. and comply with all regional and local standards is an undertaking. Selecting each component and device to do the job. Every detail. if applicable A medium voltage switchgear is a built-to-order product with many details to be considered and many selections to be made.SUBSTATION COMMISSIONING COURSE Page 36 of 46 Design and Proof Testing The design and proof testing of the assembly to show compliance with applicable standards includes. control devices. latches and interlocks • Breaker operation at minimum.” Circuit breaker testing includes. be acceptable to the customer. but is not limited to: • Component nameplate verification for compatible application • Dielectric tests • Mechanical testing of all operational parts and devices • Control wiring continuity verification • Operation of all relays. These production tests are also referred to as “routine tests. meters and other devices • Control wiring insulation tests • Instrument transformer polarity verification tests • Sequence of operation tests. but is not limited to: • Control wiring insulation test • Charging motor insulation test • Operation of switches. but is not limited to: • Short circuit testing • BIL testing • Dielectric testing • Continuous current testing • Mechanical life testing • Thermal testing • Environmental testing Production Testing Production testing of an assembly is performed in compliance with specific standards for the circuit breaker and the assembled housing individually. from the electrical and mechanical Page 36 of 46 . and rated control voltages • Vacuum interrupter operation and withstand tests • Breaker contact resistance • Closing and opening timing tests • Dielectric tests The assembled housing’s testing includes. instruments. maximum. down to the finish and composition of the structure must be considered.SUBSTATION COMMISSIONING COURSE Page 37 of 46 requirements. Page 37 of 46 . ANSI American National Standards Institute. Bus Joint The connection between the main bus and a circuit breaker (or other devices). Common Aisle An outdoor installation solution for very large assemblies. it can be reset to protect the circuit again. relays and other control equipment are usually mounted. Arc-Resistant A special certification that equipment must have for use in certain circumstances. This is where instruments. Continuous The amount of current the breaker can carry continuously at 60 Current cycles without exceeding the temperature rise limit. Allow the circuit Page 38 of 46 . The design of arc-resistant equipment is dedicated to the safe control and release of arc-related overpressures. in which vertical structures are on both sides of the aisle. Circuit Breaker A compartment in a medium voltage switchgear assembly that Compartment contains and electrically connects one or more circuit breakers. contactors and other devices. Control Power A transformer that provides a safe. Extension Rails A common feature of the circuit breaker itself. After tripping to break the circuit. Auxiliary An optional compartment in a medium voltage switchgear Compartment assembly. Glossary of Terms Aisle Part of a sheltered aisle switchgear installation. Circuit Breaker A reusable overcurrent protection device. Connected accessway for multiple vertical enclosures in an outdoor installation. A Switchgear variation on sheltered aisle switchgear. usually located above or below a circuit breaker compartment. Bus joints must be insulated. Weatherproof access doors are normally supplied at both ends of the aisle. When the circuit Shutter System breaker is removed from its compartment. Control The space between the front of the circuit breaker and the front Compartment doors of the assembly.SUBSTATION COMMISSIONING COURSE Page 38 of 46 4. It was organized to simplify and standardize production and construction. meters. reasonable low voltage Transformer source for relays. Used when there is a significant volume of auxiliary and/or control equipment required in the assembly. the compartment’s fixed primary conductors are automatically covered to prevent contact with live primary current-carrying parts. according to ANSI charts. Automatic Circuit breaker compartment safety feature. often made of silver-plated copper. In medium voltage switchgear assemblies. When the circuit breaker is levered into the CONNECTED position. A reusable overcurrent protection device designed to protect a panel downstream from a medium voltage switchgear assembly. A professional organization of scientists and engineers whose purpose is the advancement of engineering.SUBSTATION COMMISSIONING COURSE Feeder Circuit Breaker Finger Cluster Ground Bus IEC IEEE Lever Line Compartment Main Bus Main Bus Compartment Page 39 of 46 breaker slide out of its compartment easily for inspection. A configuration of spring-loaded conductive fingers mounted on the circuit breaker. the main bus usually takes the form of solid copper bars. This organization is associated with equipment used internationally. Assembly designs usually permit entry and/or exit of cable or bus from the top or bottom of the compartment. its finger clusters engage the circuit breaker compartment’s stationary primary conductors to make electrical connection. usually three per set. Abbreviation for International Electro-technical Commission. A grounded bus that runs the length of the assembly. Institute of Electrical and Electronic Engineers. A term to describe the act of moving a circuit breaker from one position to another. A compartment in a medium voltage switchgear assembly through which the main bus runs. For safety reasons. A set of electrical conductors. and is normally located in the lower part of the line compartment. These individually insulated conductors provide for multiple connections into the electrical system. Page 39 of 46 . Space is provided in this compartment for line terminations or other special devices. the ground bus is capable of carrying the rated short circuit current of the installed circuit breakers for a certain amount of time. A special certification that equipment must have for use in certain earthquake-prone zones. An outdoor enclosure is constructed around an indoor switchgear assembly with an aisle constructed as part of the enclosure at the front of the assembly. Typically associated with medium voltage equipment. An arc extinguishing technology involving the use of sulfur hexafluoride gas. An outdoor installation solution. Basically. An outdoor installation solution. Typically associated with low voltage equipment. associated control devices. but not necessarily separated by barriers. removable circuit breakers with an insulated main bus. and must be supplied by all manufacturers. the assembly of a weatherproof enclosure around an indoor switchgear assembly. An integrated assembly of compartmentalized. An outdoor installation solution. Helps ensure safe and proper interfacing between the circuit breaker and its compartment. Equipment in the assembly is enclosed. and separated by metal barriers into individual compartments. Encloses all the equipment in one weatherproof house. the construction takes place at the manufacturer’s location and then moved to the installation site A feature of both the circuit breaker compartment and the circuit breaker itself. and auxiliary equipment designed to provide medium voltage circuit protection Equipment in the assembly is enclosed. Abbreviation for National Electrical Manufacturers Association.SUBSTATION COMMISSIONING COURSE Main Circuit Breaker Medium Voltage Switchgear Assembly Metal-Clad Metal-Enclosed NEMA Outdoor Aisleless Switchgear Outdoor Control Room Safety Interlock SeismicallyQualified SF 6 Sheltered Aisle Switchgear Surge Arrester Page 40 of 46 Also “Main Breaker.” A reusable overcurrent protection device designed to protect an entire medium voltage switchgear assembly. Normally. Page 40 of 46 . A device that protects equipment from electrical surges. Interlocks are required by governing standards. An organization of manufacturers of electrical products. A metal enclosure for the other switchgear components. A switch gear assembly can consist of practically any number of adjacent vertical structures. Page 41 of 46 . Because the environment inside the interrupter envelope is a vacuum. protective and regulating equipment.SUBSTATION COMMISSIONING COURSE Switchgear Vacuum Interrupter Vertical Structure Voltage Transformer Page 41 of 46 An assembly of switching and interrupting devices. an arc cannot be sustained easily. Also “potential transformer. along with control.” A step-down transformer that steps down supplied voltage to a voltage usable by control components such as relays and meters. An arc extinguishing technology. Features a pair of separable contacts enclosed in a vacuum-tight envelope. metering. A medium voltage switchgear assembly can be composed of as many as five different types of compartments. The exact dimensions of the vertical structure are dictated by the __________ _______ and _____________ _______________ for the application.SUBSTATION COMMISSIONING COURSE Page 42 of 46 5. Medium voltage switchgear is defined by its metal _______ construction. In your own words. 1. 5. The circuit breaker compartment accommodates the circuit breaker with a number of provisions. ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ 6. 2. The circuit breaker compartment is one of them. ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ 4. Name three of them. Self Test Quiz Quiz 1: Answer the following questions without referring to the material. Page 42 of 46 . Medium voltage refers to a voltage range from __________ to __________. Name three others. define the generic term “switchgear.” _____________________________________________________________ _____________________________________________________________ _____________________________________________________________ 3. means to move the breaker in and out of the enclosure. protective and regulating equipment. 3. auxiliary Compartment 4. The exact dimensions of the vertical structure are dictated by the voltage class and specification requirement for the application. 5. means to make primary and secondary connections. line Compartment. 2. metering. Name 3 of them: • An enclosure for the breaker. along with control. The circuit breaker compartment accommodates the circuit breaker with a number of provisions. control Compartment Area. Switchgear is assemblies of switching and interrupting devices. Page 43 of 46 . safety interlocks and extension rails. Types of compartments other than the breaker • Main Bus Compartment.SUBSTATION COMMISSIONING COURSE Page 43 of 46 Answer to Quiz 1: 1. Medium voltage refers to a voltage range from 1000 to 38 Kv. 1. There are two primary approaches to outdoor switchgear assembly installations. 2. while maintaining the rated ______________ _______________ established by standards. _____________________________________________________________ _____________________________________________________________ _____________________________________________________________ _____________________________________________________________ 3. In your own words. ____________________________________________________________ ____________________________________________________________ 4. ANSI design and proof testing for switchgear assembly includes many types of tests. describe where controls are generally found in a switchgear assembly.SUBSTATION COMMISSIONING COURSE Page 44 of 46 Quiz 2: Answer the following questions without referring to the material just presented. ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ Page 44 of 46 . Seven types were mentioned. Main bus conductors are sized to handle the __________. Name two of them. Name four. Main bus conductors are sized to handle the current. The space between the front of the circuit breaker and the front doors of the assembly is generally considered as the control compartment area.SUBSTATION COMMISSIONING COURSE Page 45 of 46 Answer to Quiz 2: 1. 3. Doormounted devices are viewable with the door closed. 2. it could be located in an auxiliary compartment. Three primary approaches to outdoor switchgear assembly installations are: Outdoor aisle-less switchgear. Thermal and Environmental. while maintaining the rated temperature rise established by standards. Sheltered aisle switchgear (or common aisle switchgear). BIL. Four of seven types of ANSI proof testing are: Short circuit. Dielectric. If there is a large volume of control equipment. 4. Page 45 of 46 . Continuous current. Mechanical life. ca [4] ANSI – American National Standards Intitute http://www.nema.org/ [3] CSA – Canadian Standards Association http://www.org [6] IEC – International Electrotechnical Commission http://www.electrofed. References and Suggested Readings: Acknowledgement: Special thanks to Clayton Engineering Company who allowed the use of their graphics and education materials for inclusion in this document. References and Suggested Readings [1] Caylton Engineering Company http://www.htm [2] NEMA – National Elelctrical Manufacturing Association http://www.org [5] IEEE – Institute of Electrical and Electronic Engineers http://www.SUBSTATION COMMISSIONING COURSE Page 46 of 46 6.iec.ieee.claytonengineering.com/cecoweb/pittsburgh. Acknowledgement.csa.ch/ [7] Electro Federation Canada http://www.ansi.com/councils/EEMAC/ Page 46 of 46 .