PARTICULAR SPECIFICATION E11: GENERAL ELECTRICAL EARTHING AND LIGHTNING PROTECTION

Transcription

1 E11 : General Electrical Earthing and LIGHTNING Protection PARTICULAR SPECIFICATION E11: GENERAL ELECTRICAL EARTHING AND LIGHTNING PROTECTION Review of Mechanical / Electrical and Control / Instrumentation Standards, plus New Design Guidance Rev Date Description Signature: JW Wastewater Partnership Signature: APPROVAL FROM JOHANNESBURG WATER

2 PARTICULAR SPECIFICATION : VOLUME E11 : GENERAL ELECTRICAL GENERAL EARTHING AND LIGHTNING PROTECTION CONTENTS E Standards... 2 E Particular Specifications to be read in conjunction with this specifications... 2 E Earthing Philosophy... 3 E Common Earth... 3 E Bonding... 3 E Earthing of Substation Buildings... 4 E Earthing of Miniature Substations and Transformers... 5 E Earth Continuity Conductors... 5 E Instrument Earth... 5 E Earthing of Distribution Boards... 6 E Earth Resistivity Test... 6 E Tests to be Carried Out... 6 E Lightning Protection Philosophy... 6 E Earthing... 6 E Protected Areas... 7 E Surge Protection... 7 E Main Distribution Board... 7 E Other Distribution Boards... 7 E Data and Communication Cables... 7 E Induced Surge... 8 E Specific Surge Protection... 8

3 This specification covers the detail requirements of the general earthing and lightning protection to be installed under the contract. The latest edition, including all amendments up to date of tender of the following particular national and international specifications, publications and codes of practice shall be read in conjunction with this specification and shall be deemed to form part thereof: E Standards The earthing and lightning protection of all installations shall comply with the following standards and statutory requirements (as amended): a) SANS The protection of structures against lightning b) SANS Series c) SANS Code of practice for the wiring of premises d) SANS The design and installation of an earth electrode e) Act 85/1993 Machinery and Occupational Safety Act E Particular Specifications to be read in conjunction with this specifications The following particular specifications shall be read in conjunction with the Project Specification: G01: PARTICULAR SPECIFICATION FOR COLOUR CODE G02: PARTICULAR SPECIFICATION FOR CORROSION PROTECTION E06: ELECTRICAL MEDIUM AND LOW VOLTAGE CABLE INSTALLATION E05: LOW VOLTAGE POWER AND CONTROL CABLE E08: WIRING The Contractor shall appoint an earthing and lightning protection specialist to perform resistance measurements. The obtained measurement/values shall form part of a certificate of compliance issued by the specialist, who shall be a professional Engineer, which shall contain: An evaluation of the obtained results; A statement that the earth network and earth electrode resistances are in accordance with the standards and requirements listed in Clause ; and, if necessary; Details of areas of non-conformance in this regard. Two copies of this certificate shall be submitted to the Engineer before handing over of any repair, modification or new installation involving earthing or lightning protection systems.

4 E Earthing Philosophy The earthing philosophy is based on two broad principles: Common Earth: The installation shall make use of only one earth system. Every earth shall be bonded to the main plant earth. Bonding: All Equipment likely to be subjected to surge currents shall be securely bonded together and to the earth network. E Common Earth Unless otherwise specified herein, the installation shall make use of only one earth system. This implies the following: Where an installation may typically consist of a main building or plant and one or more satellite subsystems, the various earth networks shall be interconnected to form one earth system. All main distribution boards and sub distribution boards shall be connected to an earth bar that is connected to the main earth conductor. Only in the rare instance of a subsystem being totally isolated, with no cables, pipes, fences or other conductive structures connecting it to the rest of the installation, may a system be provided with a separate earth network. Mains or safety earth networks and so called clean earth net-works shall be connected to each other, preferably somewhere outside the "clean" area. E E Bonding General The following items shall all be securely bonded, in an electrically continuous manner, to the earth network: E Earth busbars All metal parts (e.g. enclosures, lighting masts, frames, steel columns, gates fencing, pipes, cable ladders and trays, roofs and steel reinforcing). E Cable Armouring and Glands Cable screens. Safety or mains earth. Clean earth. Steel conduit. E Earthing Electrodes Bonding leads shall be short and shall run in straight or smoothly contoured routes. s such as fences, pipes, cables and conduit shall be earthed at both ends.

5 E Bonding Conductors Unless otherwise specified herein, bonding shall be done by means of 16 mm², green PVC insulated, hard drawn, stranded copper conductor and crimping lugs or ferrules. E Lugs Where the earth network is connected to the electrical system or bonded to structures, the earth or bonding conductor ends shall be fitted with lugs. The lugs shall be secured by means of a hydraulic compression crimping tool with hexagonal dies or by means of brazing or silver soldering. Dimple type indent crimping will not be acceptable. E Cable Armouring At cable ends, the armouring shall be made off separately and be fitted with lugs. Armouring strands shall not be cut away to fit lugs. Cable armouring shall be bonded to the earth network at both ends of the cable. E Cable Screens Cable screens shall normally be bonded to the earth network at both ends of the cable. In cases where cable screens are used for signalling purposes (e.g. coaxial cables), the screens shall either not be earthed or earthed at one end only, depending on the application. If not specified, the screens shall be earthed at one end only. In addition, the cable shall either run inside earthed steel conduit or a separate earth conductor shall be installed alongside the cable. Screens of 600/1000 V grade single core cables shall be earthed at one end only. E Cable Ladders and Tray Where there are breaks in the cable ladder or cable tray installation (e.g. at joints, bends or wall penetrations), the two sections shall be connected to each other. Both ends of cable ladder and cable tray runs shall be bonded to the earth network by means of 35 mm², stranded, bare copper conductor. E Roofs One 10 mm² bare copper conductor shall be installed over the full length of the ceiling void. This conductor shall be fixed to the top purlin and connected to the main earth conductor or earth bar of each distribution board. Conductive roof sections and gutters shall be connected to this conductor, at 15 m intervals, by means of 12 x 0, 8 mm copper strapping and galvanized bolts and nuts. Different roof levels and sections shall be bonded to each other. E Non-conductive Wireways Cables in PVC conduit or non-conductive sleeves shall be installed with stranded, bare copper earth conductors. These conductors shall be bonded to the earth network and other conductive items in the vicinity. E Earthing of Substation Buildings A substation copper earth bar, 50 mm x 6 mm x 600 mm, shall be fixed against the wall with cadmium bolts, in a suitably positioned cable duct, 200 mm above floor level. Ten holes of 10 mm diameter shall be provided in the earth bar. All earth conductors shall be stranded copper conductors with crimped cable lugs. The

6 following earth conductors shall be installed via the cable ducts: Two 70 mm separate conductors, from the medium-voltage switchgear earth bar or earth bolt to the substation earth bar. One 70 mm conductor from every medium-voltage cable box and/or cable box stand. One 70 mm conductor from every low-voltage board/panel. All double earth conductors shall be bound together neatly with plastic cable ties and be attached with the same bolt. Only cadmium plated bolts and nuts shall be used for fixing earth conductors. Final earthing shall be by means of three 70 mm 2 stranded copper conductors extending from the earth bar away from the substation, and installed in the ground in cable trenches, 900 mm deep and 50 m long and as close to 120 apart as possible. Furthermore, a 70 mm 2 bare copper earth conductor in a closed circuit around the substation building shall be installed at a depth of 900 mm and both ends shall be fixed together and to the earth bar. After completion the subcontractor shall arrange for an earthing-resistance test to be carried out in the presence of the engineer. Any further earthing that may be required will be determined by the test results. E Earthing of Miniature Substations and Transformers The earth shall comprise of a 70 mm² bare copper earth conductor installed in a ring around the miniature substation base at a depth of 1 metre. 1,8 metre earth spikes shall be installed at each corner of the miniature substation and shall be connected to the earth installed around the miniature substation. Two further 70mm² bare copper earth conductors connected to the earth spike at each corner of the miniature substation shall be installed radially away from the miniature substation for a distance of six metres. A 1,8 metre earth spike shall be installed at the end of the radial earth conductors. All earth conductors shall be terminated at the miniature substation, using crimped lugs securely bolted to the earth bar. The ends of the copper conductors shall be cleaned for a distance of 30 mm to obtain a good electrical contact with the lugs. All earthing shall be done to the satisfaction of the engineer. E Earth Continuity Conductors Bare stranded copper earth continuity conductors shall be laid with all low-voltage cables from the miniature substations or main distribution board to the distribution kiosks and distribution boards. Crimped lugs shall be used for the termination of the earth conductors. E Instrument Earth In each motor control centre a separate instrument earth shall be provided. The instrument earth shall consist of a 50 mm x 6 mm x 600 mm solid copper earth bar which shall be fixed against the wall of the substation (above the cable trench) with cadmium bolts. Ten holes of 8 mm diameter shall be provided in the earth bar. All earth conductors shall be green PVC insulated stranded copper conductors with crimped cable lugs. The following earth conductors shall be installed via the cable ducts: One 16 mm conductor from every instrument marshalling panel.

7 One 16 mm conductor from every controller on PLC. One removable link (bolted) between the instrument earth bar and the substation earth bar. Final earthing shall be as for substation earthing with the exception that the earth conductor shall be PVC covered up to the outside of the building and that the conductor size shall be 16 mm. The final earthing may share the same trench on condition that the two earths be separated by at least 400 mm. After completion the contractor shall arrange for an earthing-resistance test to be carried out in the presence of the engineer. E Earthing of Distribution Boards The earth bar or earth terminal of distribution boards and Equipment shall be connected to the earth bar of the supplying distribution board in accordance with SANS These connections shall consist of bare, stranded copper conductors, installed along the same routes as the supply cables. If the supply connections consist of conductors in conduit, the earth conductors shall be installed in the same conduit. Each earth bar shall be connected to the earth network by means of M8 lugs, brass bolts, nuts and locknuts. Unless otherwise specified herein, these connections shall be effected by means of 16 mm² copper earth conductor. Each earth conductor shall be connected to the busbar with its own bolt and nut. E Earth Resistivity Test Where specified in the Projection Specification, earth resistivity tests shall be carried out prior to the installation of the earthing installation by a Specialist Contractor and the results shall be submitted to the Engineer. E Tests to be Carried Out After completion the Contractor shall arrange for an earthing-resistance test to be carried out in the presence of the Engineer by a Specialist Contractor. Any further earthing that may be required will be determined by the test results. The following are the maximum acceptable earth electrode resistances: Main substations - 1 ohm Miniature substations and kiosks - 2 ohms Highmasts - 5 ohms. E Lightning Protection Philosophy The lightning protection philosophy is based on sound earthing and the creation of relatively surge free areas. These areas will be referred to as protected areas. E Earthing The installation shall be earthed as specified above.

8 E Protected Areas Main installations and subsystems shall be established as so-called protected areas. Protected areas shall be surrounded by a ring earth and all Equipment shall be bonded to the earth network as specified herein. All cables crossing the barriers of the protected area into the unprotected environment shall be supplied with surge protection. All conductive Equipment, such as pipes and fences, crossing the barriers of the protected area into the unprotected environment, shall be securely bonded to the earth network at the point of entry into the protected area. E Surge Protection Surge protection shall be provided to all power, data and communication cables entering or leaving the protected area. All types of surge protection utilized shall have a serviceability indication facility. E Main Distribution Board Course protection in the form of a high capacity 100KA surge arrester shall be installed at the main low voltage distribution board of the installation. All three phases, as well as neutral, shall be connected to earth via the arrester. The surge arrester shall be solidly bonded to the distribution board earth bar by means of 16 mm² green insulated copper conductor and shall be as accessible as circuit breakers and other distribution Equipment fitted to the distribution board. E Other Distribution Boards Distribution boards, other than the main low voltage distribution board, feeding loads outside the protected area or being fed from outside sources, shall be supplied with 15kA overvoltage arresters. These arresters shall be installed between each phase and earth, as well as between neutral and earth. Distribution boards, other than the main low voltage distribution board not feeding loads outside the protected area or being fed from outside sources, shall be supplied with 6.5kA overvoltage arresters. These arresters shall be installed between each phase and earth, as well as between neutral and earth. The overvoltage arrester units shall be solidly bonded to the distribution board earth bar by means of 4 mm² green insulated copper conductor and shall be as accessible as circuit breakers and other distribution Equipment fitted to the distribution board. Where use is made of more than one set of busbars in the same distribution board, all the busbar sets shall be provided with overvoltage arresters as specified herein. E Data and Communication Cables Data and communication cables entering or leaving the protected area shall be provided with suitable surge protection. The Contractor shall timeously submit detailed proposals of all surge and over-voltage protection Equipment to the Engineer for approval. The Contractor shall only utilise devices that are approved by TELKOM and which have levels of signal attenuation less than that specified as acceptable by the equipment manufacturer.

9 E Induced Surge Cable sections between surge protection Equipment and the barrier of the protected area may induce surge currents in nearby cables and shall be regarded as being part of the unprotected environment. No other cables shall be installed in the same trench or wireways as these cables. In addition, the following sets of cables, along parallel routes, shall not be installed closer than 500 mm from each other: "Raw" power and UPS power cables. Data/communication and mains power cables. E Specific Surge Protection The measures specified are aimed at generally limiting the impulse level to 1000 V. The Contractor shall ensure that all electrical and electronic Equipment will be suitable for continuous, reliable operation under these conditions and that all such Equipment is adequately protected in accordance with their own withstand levels, whether such protection has been specified or not. Earthing of substation building... Sum The tendered rate shall include full compensation for the supply of all material required and the installing of the earthing system and shall include for the testing of the earthing installation by a specialist contract. Earthing of miniature substations and transformers... Rate The t conductor and lugs, the laying of the bare copper conductors, the termination of the conductors and the connection thereof to the earth bar. Supply and lay earth continuity conductors... m The tendered rate shall include full compensation for the supply and laying of the specified earth continuity conductors. Terminating of earth continuity conductors... No The tendered rate shall include full compensation for supplying all the material required to terminate and connect the earth continuity conductors and the connecting thereof to the earth bars in the miniature substations, main distribution boards, distribution kiosks and distribution boards.

10 Extra over for the supply and installation of additional earth spikes of specified length including clamps for the connection of earth conductor... No The tendered rate shall include full compensation for the supplying and installation of the earth spikes. Provision for additional earthing as required...prov sum The provisional sum provided shall include for any additional earthing which may be specified by the Engineer after the acceptance of the contract. The Contractor shall submit a written quotation to the Engineer when requested to by the Engineer and shall not commence with the installation of any additional earthing without the written instruction of the Engineer. Provide an instrument earthing system... Sum The tendered rate shall include full compensation for the supply of all material required and the installing of the instrument earthing system and shall include for the testing of the earthing by a specialist contractor. Earth resistivity tests... No The tendered rate shall include for the carrying out of the earth resistivity tests by a Specialist Contractor. The unit for measurement shall be per point where such tests have to be carried out. Earth tests... No The unit of measurement shall be the number of earth tests undertaken. The tendered rate shall include full compensation for providing the equipment required to undertake the tests and the undertaking of the tests.