Section 531_grounding and Lightning Protection System

March 19, 2018 | Author: hani_pilevar3778 | Category: Cable, Electrical Conductor, Electrical Resistivity And Conductivity, Electrical Connector, Chimney



SECTION 531 - GROUNDING AND LIGHTNING PROTECTION SYSTEMNote: The highlighted texts are out of scope of BOP contract and only considered for contractor information. 1 1 A. Current transformers. in section 410. but not limited. Steam turbine and auxiliaries. Cable system. erection and testing of grounding. The primary grounding system for whole power plant is in the scope of the BOP contractor. in section 523. is subject to scope of work of MAPNA or BOP contractor accordingly: Power transformers (main. in section 46. Potential transformers. in section 583. station. The secondary grounding system for the following items. in section 584.PART 1 1. including transformer ground terminal in section 511. Generator and Auxiliaries. Generator. GENERAL Description Definition Grounding shall mean grid. connections. Related Work Specified in Other Sections Following items of works related to work of this section covered by other sections are. equipment and other materials and measures required to complete the grounding of generating plant and buildings under this contract. in section 585. in section 522. but not limited to those. Diesel Generator Set. manufacture. Transformer. in section 545. Also provision shall be made for the protection of building/equipments against lightning (NFPA 780). Work of this section includes design. in Section 516. and unit) Auxiliary Transforms 2 . High voltage and low voltage motor. Auxiliary power system. in section 532.6 kV switchgear. Extent of Work The extent of work shall include generating plant primary. ground rods. Control and Relay panels. Lightning arresters (surge arresters). in section 41. 6. Lighting. B. secondary grounding and lightning systems. in section 521. in section 515. including conduit and cable tray. as noted: (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) C. 1. fuel) Piping systems All other metallic items which may come in contact with or establish a dangerous voltage.1 Standards Work of this section shall comply with the requirements of the latest editions of IEC. ANSI. oil. BS. Alternative Minor alternations in conductor and connector locations to suit the equipment specifically offered will be considered.- D. Latest Revisions of publication listed below form part of this specification: ANSI A10 "ANSI Standards about Safety" 3 . NEMA. IEEE. (Standards and codes of other origin may be accepted with the Engineer's approval). Such alternations shall require the approval of the Engineers. and/or other contractual standards. Indoor switchgear Distribution panels Stack Main Buildings structures (Turbine hall and main and auxiliary boilers) Auxiliary Buildings Lighting and AC distribution panels Battery chargers and DC & UPS system Relay and control panels Cable trays Lightning Arresters and surge arresters Metallic conduits Wire armouring on power and control cables Main Generators Diesel Generators Grounding meshes and mechanism box of isolators Electric motors/pumps/fans Steel structures/gantries/towers Turbines Main and Auxiliary Boilers Main and Auxiliary Cooling Towers Fuel handling and storage tanks(Water. IPCEA. Bar and Wire for General Electrical Purposes BS EN 13601 Copper and Copper Alloys . Earth Potentials of a Ground System IEEE 81. Round of Wire Manufacture Electrical Conductors BS 13601 Copper And Copper Alloys . Surface Impedance. Extended or Interconnected Grounding Systems 4 .IEEE C2 BS EN 62305-3 National Electrical Safety Code Protection Physical Hazard against Damage to Lightning Structures Part and 3: Life IEC 62305 NFPA 780 Protection against Lightning Standard for the Installation of Lightning Protection Systems BS EN 13602 Copper Copper and Copper for Alloys the - Drawn.Copper Rod.2 Guide for Measurement of Impedance and Safety Characteristics of Large.Specification BS EN 50020 Electrical Apparatus for Potentially Explosive Atmospheres .Intrinsic Safety "I" BS 2754 Memorandum Construction of Electrical Equipment Protection against Electric Shock IEEE 80 IEEE 81 Guide for Safety in AC Substation Grounding Guide Ground for Measuring Earth and Resistivity.Copper Rod. Bar and Wire for General Electrical Purposes BS 951 Electrical Earthing Clamps for Earthing And Bonding . 3 A. Quality Assurance Design Criteria Apart from the specific requirements of this section. considered to last for a period of 0.2. 1. The maximum ground fault currents to be used when designing the ground grid shall be determined from maximum fault levels specified for HV Bus in Volume 2 section 50 general engineering. grounding and lightning protection shall be designed. The main grounding grid shall be formed from copper horizontal conductors at intervals of not greater than 10 meter and copper weld rods.5 second and a maximum temperature of 250C for bolted joints and 450C for brazed joints.IEEE 141 Recommended Practice for Electric Power Distribution for Industrial Plants IEEE 142 Recommended Practice for Grounding of Industrial and Commercial Power Systems IEEE 100 The Authoriative Dictionary of Ieee Standards Terms IEEE 665 IEEE 1050 Guide for Generating Station Grounding Guide for Instrumentation and Control Equipment Grounding in Generating Stations IEEE 1100 Powering and Grounding Sensitive Electronic Equipment 1. manufactured and tested according to the requirement of the standards referred to in IEEE 80 Article 1. Station ground grids shall be designed to obtain a station ground resistance of 0.3 ohms or less.4 Submittals 5 . A. 80 that safety of touch and step potentials. Calculation to show fault current sections of the grounding grid. The connectors shall be copper or tinned copper where fitted to aluminium. Detail drawings showing all equipment. Ground rods shall be "copper weld" minimum diameter 1. The conductor for connections between equipment etc. station ground fault potential rise.1 PRODUCTS Materials The materials used shall be as follows: The grounding conductor for the plant main grid shall be standard soft drawn annealed copper. minimum length. 3 meters. Detailed description of the various connectors connecting process used to form the grounding lightning system. with minimum spacing of 3 meters. Grounding conductor shall be connected to equipment by bolted connections. The data shall include but not be limited to the followings: (1) (2) (3) Layout drawings of each overall grounding grid.75cm. and main grid shall be of the same current carrying capacity as the main grid conductor and shall be of stranded soft drawn annealed copper. Manufacturer's Calculations capacity of and and (4) various B. conductor diameter. 6 . Minimum contact area of the conductor to the connector shall be 10 cm2. with a minimum of seven strands. Shop Drawings and Manufacturer's Literature Submit detailed drawings and calculations pertaining to each item supplied this section in accordance with the Article entitled "shop drawings" in submittals section 53.. The contractor shall check the soil resistance at site and shall show by the calculations carried out according to IEEE standard No. PART 2 2. The conductor size shall be 185 mm2 minimum. and calculation ground and lightning design are correct. Where grounding conductors would be exposed. At the completion of the project. No. cable supports. 3. the balance of material will be turned over to the client as spare parts. it can be decided as a reference of grounding conductor size selection for different equipment. Insulated grounding conductor shall be used for connecting power transformer core grounding resistor to the ground grid. The cross . It is sufficient to connect collective pipelines. An additional quantity representing ten percent of the total quantity of all material required for the completion of this section of the works shall be included in the shipment to cover possible damage or loss during shipment or erection. 1 2 Equipment 6.section of grounding conductor shall be such as to safely carry the appropriate fault current for the necessary length of time.All buried joints shall be either welded or brazed. shall be grounded. All equipment frames and metal parts of indoor/outdoor apparatuses including main pipes. etc.6 kV Switchgear 400 V Switchgear Conductor Size mm2 95-185 95-185 7 .1 A. vessels crane tracks. main supporting system and tracks at interval of 20 meters.8 meter below finished grade. Insulated cable or copper ground bus supported on insulators shall be used for connecting lightning arresters to lightning arrester counters. Installation and Erection General The main grounding grid shall be buried at depth of not less than 0. From the table below. the green/yellow PVC insulated grounding conductors suitable for a power frequency voltage to earth of 250 V (or conductor inside the plastic conduits) shall be used. 3 4 5 6 7 8 9 10 Control Panel Generator Transformers PT & SA . MV & LV switchgear shall be grounded at both ends of switchgear row.NGR Terminal Box Lighting Distribution Board High Voltage / MV. the additional connection can be considered for switchgear row having a length more than 15m.g. Motors Low Voltage Motors S<16 16<S<35 S>35 (S: Cable Phase Conductor Size in mm2) Tray system 70 185 185 185 50 50 185 S 16 S/2 95 11 Transformer neutrals and lightning arresters shall be connected directly to the earth electrode and main grid which their grounding conductors shall not be used for other equipments also the a. distribution boards and field mounted equipments etc. Do not use ground of lightning arresters as ground connection for other 8 . subjected to the engineer approval. Power cables carrying alternating currents shall have their armour bounded to the grounding system at both ends. The generator / transformers shall be grounded at two opposite side points. - - Ground all equipment frames to main ground grid. trays with I&C cables in cable ducts shall be covered to protect them against lightning and interference voltages. The cable tray/ladder sections shall be connected to the main grounding mesh interval between 20 to 30 m. conductors shall be short and straight.. may be connected to the earth through their associated cable armour. Grounding of screens of cables (less than 60V) for binary and analog signals shall be done at one end at electronic cabinet (I&C panels). small circuit breaker protected motors. Minor items of plant e.m. Electrically bond the metallic cable tray and conduit at all mechanical joints and connect at intervals to ground grid. Obtain approval of the client’s representative before covering the ground grid by permanent material. Metallic conduits shall be bonded at all mechanical joints and connected at intervals (subjected to the engineer) to main ground grid. Sensitive equipment using integrated circuits shall have their clean ground system connected to an independent ground mesh or the main ground system (subjected to the engineer's approval). contractor shall notify Engineer in writing as soon as installation is completed and at least 24 hours before embedding in concrete so Engineer may inspect quality of work. Make all connections to equipment by mechanical connections bolted or clamped to a vertical face with sufficient pressure and contact area to prevent burning due to fault currents. Provisions shall be made for restricting touch voltage to safe limits as per standard IEEE 80. All other connections shall be by an endothermic welding All equipment frames shall be grounded to the main ground grid. Each structure column shall be grounded where required by placing grounding conductor on inside surface of structure legs on girder chord angles and supported neatly by bolt type connectors. Keep ground straight. connections to lightning arresters short and Connections to equipment frames and to galvanize steel structures shall be made using bolted connections. All permanent / buried joints and connections shall be done by cad weld method or by an approved compression type method. and step Ground conductors in the switchgear and relay room and plant area shall be run in cable tray. Equipment and structures shall be connected not less than 300 mm above finished grade using bolted connectors. Should any conductor need to be embedded in concrete. The grounding system shall be so designed that all sections 9 . 3. luminaries frames. Air terminals shall be at least 30 mm diameter stainless steel rods. never upwards.e. Whenever a conductor is used to bond a metallic component to the lightning rod down conductors.2 Field Quality Control The resistance of the complete grounding system and step/touch voltage shall be measured by the contractor with an approved form of earth resistance system. the connection should run downwards from the connected part. lead covered medium hard drawn copper. and all in accordance with NFPA-780. If the grounding resistance of 10 . This shall comprise a sufficient number of air terminals. The value of the ground resistance for the stack grounding system shall not exceed one ohm. All power plant buildings which do not fall within the 15 degrees of protective cone of the stacks shall have their own lightning protection. shall be bonded to the nearest portion of the down conductor system. Liners. Lightning conductors and the stack grounding system shall not be used for grounding wiring systems or other electrical equipment. ladders.. etc. Reinforcing bars of the stack shell or the steel stack and its supports must be connected together and to the lightning protection down conductors at the top and at the bottom. shall be connected to the protective grounding system at both the top and bottom. lightning cables. The metal platforms shall be bonded to the internal down conductors. also the sheaths or conduits of cables which are attached to the stack structure shall be grounded. To prevent lightning damage to any control. Conductors for the lightning protection system and the down conductors for the stack grounding shall be stranded. Individual sections of the ladder shall be bonded together.can be isolated to do grounding measurements for each section after completion of installation. all conduits carrying cables shall be bonded by copper cable at their highest point to the nearest internal down conductor of the lightning protection system. All metal parts of the stack shall be bonded to the grounding system.. etc. Other metal parts i. The stack lightning protection shall be in accordance with the recommendations of the latest edition of NFPA-780. all suitably grounded. additional ground rods shall be used or an auxiliary ground grid may be installed to reduce the grounding resistance. section 5 or other contractual standards.the grid is greater than 0. The site testing of lightning system shall be as per BS 6651. 11 . Carry out testing of equipment in accordance with the approved test program on completion of installation.3 ohms.
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