BULLETIN Title: Tunnel site electrical safety standards requirements - PowerPoint Presentation

1. BULLETINTitle: Tunnel site electrical safety standards requirements

2. Tunnel Boring Machines are designed, manufactured, including the day to day management of the operational execution works by recognised international standards (of which there are many. Germany/UK/Japanese/Indian & Others). These standards are to be followed to ensure minimum standards of regulations are adhered to. Furthermore these guidelines are recognised by the International Tunnelling Association (ITA)In India the common standard for Tunnelling Machinery Equipment would be covered by following European regulations;BSEN6164 – Health and safety in tunnelling in the construction industry.BSEN16191 – Tunnelling machinery-Safety requirementsSite electrical safety requirements(arrangements)

3. Company and site management hierarchyPlanning, management and control of the electrical systemSafe system of workMains supply connectionSite installations 5.1. Voltage 5.2. Fault ratings 5.3. Earthing 5.4. Residual current devices (RCDs) 5.5. Waterproofing, dustproofing, vibration, mechanical stress and impact protectionSite electrical safety requirements(arrangements) 6. Cables 6.1. Power supply cables 6.2. Trailing and flexible cables6.3. Control system cables6.4. Storage of cables6.5. Installation of cables6.6. Reuse of cables6.7. Fire Risk associated with cables6.8. Cable reeling drums7. Joints and termination8. Transformer and switchgear in tunnels9. Electrical plug and sockets10. Lighting installations11. Motors and generatorsCONTENT

4. Company and site management hierarchySite electrical safety requirements(Arrangements)As per BS6164 section 25.1: Appointments of the Electrical Duty Holders for any site along with the person in overall charge of implementing the ESRs should be made or endorsed by the company senior electrical engineer in the principal contractor’s organization in accordance with the site Electrical Safety Rules and should be presented on a clear organogram. The guidance in the IET Code of Practice for Electrical Safety Management for electrical safety which includes definitions for the following roles should be followed: • Authorizing Officer AO • Authorizing Engineer AE • Senior Authorized Persons SAP • Authorized Persons AP • Competent Persons CP

5. Site electrical safety requirements(Arrangements)2. Planning, management and control of the electrical systemAs per BS6164 section 25.2: In tunnelling operations, where environmental conditions can be very severe and where high-voltage (HV) power distribution frequently has to be used, this is critically important. With regard to the appointing of electrical personnel, the development of electrical safety rules and management of site electrical systems, attention is drawn to the following standards, guidance notes, and codes of practice: The Electricity at Work Regulations 1989 [N7]; HSE publication HSR 25 [60]; BS 7375:2011; HSE HSG 230 – Keeping Electrical Switchgear Safe [61]; BS 6626; IET Code of Practice for Electrical Safety Management [62]; BS 7671; IET Guidance Notes 18th edition on conforming to BS 7671 [63]; BS EN 50110; and BS 7430:2011.A formal system should be established for the management and control of an electrical distribution system meeting the requirements of BS EN 50110 and BS 7671.

6. Site electrical safety requirements(Arrangements)3. Safe system of workAs per BS6164 section 25.5: A Safe System of Work should be in place addressing the following: Preparation of operational safety documents; Arc flash risk assessment; Implementation of manufacturers operational restrictions; Switching schedule – HV specific; Permit to work procedures; Preparation and distribution of isolation and earthing diagrams; Sanction for test; Limitation of access for non-electrical work; Regular review and update as required of network diagram; Upkeep of maintenance systems and asset register; Upkeep of maintenance records, which should be subject to periodic audit; and dealing with emergencies.

7. Site electrical safety requirements(Arrangements)4. Mains supply connectionCare should be taken as the safety of persons and works can be dependent on the continuity of power supplies to safety critical equipment including: lighting; pumping; atmospheric monitoring equipment and ventilation; compressed-air working; signalling and communications, including the emergency channel 5 system; alarms and shutdown systems; firefighting; refuge chamber; and electrically power lifting equipment'sAs per BS6164 section 25.6:

8. Site electrical safety requirements(Arrangements)5. Site installations As per BS6164 Section 25.7: Installations on construction sites should conform to BS 7375 for the distribution of electricity on construction and building sites, together with BS 4363 for distribution units.5.1. Voltages(AS per BS6164 section 25.7.2):Extra-low voltage (ELV) - not exceeding 50 V (AC or DC), between conductors or conductor and earth.Reduced low voltage supplies - 110 V, 50 Hz derived from centre tap earthed (CTE), single‑phase or 3‑phase neutral earthed (NE) transformers.,Low voltage (LV) - normally not exceeding 1 000 V AC or 1 500 V DC.High voltage (HV) - normally exceeding 1 000 V AC. or 1 500 V DC.5.2. Fault ratings(AS per BS6164 section 25.7.3):Electrical equipment should be selected according to the circuit fault level and in all cases should be capable of withstanding the full fault rating for 3 s. Where possible, actual fault levels should be reduced by the use of high-impedance transformers and neutral earthing resistors supplemented by high-speed protection. NOTE: The following nominal fault levels are common for industrial equipment: • 11 kV, 250 MVA; • 6.6 kV, 150 MVA; • 3.3 kV, 50 MVA; • 400 V, 30 MVA

9. Site electrical safety requirements(Arrangements)5.3. Earthing(AS per BS6164 25.7.4): All electrical installations and equipment should be earthed and bonded in order to reduce the likelihood of dangerous voltage rises and to rapidly clear any faults by installed circuit protection. Earthing should be in accordance with BS 7430 and BS 7671. Protection of circuits against electrical shock, short circuit and overcurrent The main protection against electrical shock short circuit and overcurrent, should be provided by the combination of the following in accordance with BS 7430, BS 7375 and BS 7671:5. Site installations

10. Site electrical safety requirements(Arrangements)5.4. Residual current devices (RCDs)(AS per BS6164 section 25.7.5): 5. Site installations The risk of electric shock often results from people making contact with unprotected energised parts of electrical equipment and earth. Contact with energised parts may occur by touching: Bare conductors Internal parts of electrical equipment External parts of electrical equipment that have become energised because of an internal fault Metallic or other conductive equipment that has inadvertently become live. RCD must have a tripping current that does not exceed 30 milliamps if electricity is supplied to the equipment through a socket outlet not exceeding 20 amps.

11. Site electrical safety requirements(Arrangements)5. Site installations 5.5. Waterproofing, dustproofing, vibration, mechanical stress and impact protection: The required degree of protection should be selected in accordance with BS EN 60529.

12. Site electrical safety requirements(Arrangements)6. Cables6.1. Power supply cables :For HV and LV power supplies other than through trailing or flexible cables, the following cable types should be used: For voltages above 3.3 kV: Low Smoke Zero Halogen(LS0H), 3-core, screened with single wire armouring and cross-linked polyethylene (XLPE) insulation, conforming to BS 7835; For voltages of 3.3 kV and below: Low Smoke Zero Halogen(LS0H), 3-core or 4-core, with single wire armouring and cross-linked polyethylene (XLPE) insulation, conforming to BS 6724. All power supply cables operating at above reduced low voltage should be of a type having a metal sheath and/or screen, which should be continuous and effectively earthed. Pilot cores should not be used for HV tunnel feeder cables where such feeders could be more than 2 km in length. Pilot earth monitoring systems have proved to be unreliable over such distances. Where pilot earth monitoring is omitted the following recommendations should be met. Tunnel cable joints should be made using bolted or resin type joints. The bolted joint should be a joint chamber, a half coupler, or similar. A plug and socket system should require the use of tools to separate the components.

13. Site electrical safety requirements(Arrangements)6. Cables6.2. Trailing and flexible cablesFor trailing and flexible cables the following should be used: For heavy mobile plant such as road headers, three power cores, pilot and earth conductors, EPR/CSP insulated, screened, PCP inner sheath, pliable armoured, PCP outer sheathed, such as Type 7, 7S, or 7M; For mobile plant such as grouting or shotcreting equipment, three power cores, pilot and earth conductors, EPR/CSP insulated, PCP sheathed, with overall metallic screen.To tie in with the possible lack of a pilot core in the tunnel power supply cable (see BS6164 Section 25.7.2), all machinery connection cables (trailing, reeling, or on mono-rail) should have metallic earth screening around each phase conductor.Control systems cables should conform with BS EN 505256.3. Control system cables

14. Site electrical safety requirements(Arrangements)6. Cables6.4. Storage of cablesThe method of storage and running out of a cable should not induce twist or mechanical stress in the cable and should be compatible with the flexibility of the cable. NOTE: Cables can be stored on drums, or coiled in a figure of eight if no drum is available. Where current is passed through a coiled cable, particular care should be taken to guard against heating effects (see BS6164 section 13.3), and the cable should be appropriately de-rated.

15. Site electrical safety requirements(Arrangements)6. Cables6.4. Installation of cablesCables should be located along the side wall of the tunnel at an elevated position to be clear of water and accidental contact by moving vehicles. Cables should be protected against mechanical damage, fire and water. Consideration should be given to the fire resistance of cable fixings in critical areas where collapsed cables could become an entanglement hazard in the event of a fire. High standards of insulation and mechanical protection along with a high standard of workmanship should be adopted in the installation of HV cables. Care should be taken to ensure that no longitudinal twists are induced in a cable during installation, as they can result in internal damage which is not visible from external inspection. Where cables are run vertically down shafts the cable should be supported. There should be support at the point of access to the shaft (suitable brackets, cable socks, etc). Cable weight should be assessed and additional support added down the shaft if required. The support should be fit for purpose, using cable clamps, trays or ladders. In vertical shafts the cables should meet the requirements of BS EN 60332-3

16. Site electrical safety requirements(Arrangements)7. Joints and terminationMining type coupling for trailing cableRobust design.Incorporates pilot circuit which kills power automatically when joint openedCoupling body is earthed.The coupler is not a switch and should not be used as one.Fixed cable joint in tunnel.Permanently jointedMust be made by electricianNo capability for disconnectionLow voltage cable connections should be in accordance with BS 7375 and BS 7671.

17. Site electrical safety requirements(Arrangements)8. Transformer and switchgear in tunnelsTransformers should be in accordance with BS EN 60076-1. Transformers in tunnels should be located as follows: In fixed substations in tunnels, generally remote from working areas; As temporary installations to suit mobile machines; Forming an integral part of, a machineIn tunnels, only transformers employing air cooling (preferable), or appropriate fire-resistant synthetic insulating/cooling liquids should be used. The liquids should be synthetic organic esters as specified in BS EN 61099 or silicone-based fluids manufactured in accordance with BS EN 60836. Only synthetic liquids which do not contain PCBs or other toxic or eco-toxic ingredients when in liquid form or in the combustion products in the event of fire should be used. Mineral-oil-filled transformers should not be used in any underground locationThe temporary nature of tunnel construction operations and the very limited space normally available should be taken into account when selecting transformers.

18. Site electrical safety requirements(Arrangements)8. Transformer and switchgear in tunnelsCast resin transformers should not be used in situations where there is a risk of combustible dust. Where high levels of protection against ingress of water or dust are necessary, and in situations where high humidity could cause problems due to condensation, the use of dry type, hermetically sealed, pressurized nitrogen-filled transformers should be used where necessary. The means of isolation of the primary side of any power transformer should be by air break, vacuum or gas-filled type switchgear, which is preferably integral to the transformer, or alternatively by similar, separate, immediately adjacent switchgear.

19. Site electrical safety requirements(Arrangements)8. Transformer and switchgear in tunnelsThe vector grouping of HV/LV transformers (details of the options are given in BS EN 60076-1) should be considered during the design of the electrical distribution scheme to: Make provision for earthing the system at appropriate points in order to prevent the voltage in any part of the system rising to a dangerous level with respect to earth. Avoid circulating currents.Provide a “star” point on the load side of the transformer.Effect safe parallel operation.Suppress, where necessary, harmonics generated by thyristor-controlled motors.

20. Site electrical safety requirements(Arrangements)8. Transformer and switchgear in tunnelsSwitchgear should be provided, wherever necessary, to isolate and protect cable runs, transformers, other distribution units and the equipment and plant for which the power is required. All switchgear should conform to the standards appropriate to the system voltage and to the circuit loadings, and should be fully protected against the foreseeable risks and expected hazards particular to its situation, which can include: • fault currents.• entry of water and dust (the minimum degree of protection as categorized in BS EN 60529:1992 should be IP 55). • methane or other flammable gas.• damage from moving plant and vehicles or other mechanical sources. Damage from blasting operations. Oil-filled switchgear should not be used underground, principally because of the fire risk. Air break, vacuum or gas-filled switchgear should be used.

21. Site electrical safety requirements(Arrangements)9. Electrical plug and socketsFor low-voltage applications rated 125 A or less, the plugs and sockets should conform to BS EN 60309-1. For operating voltages above 110 V and current ratings above 32 A, the plugs and sockets should be fitted with either electrical or mechanical interlock to prevent disconnection while live. In flammable or potentially explosive atmospheres plugs and sockets should be of the explosion-protected typeYellow – 110 voltsBlue – 240 voltsRed 415 volts

22. Site electrical safety requirements(Arrangements)10. Lighting installationsAs per BS 6164 section 25.12.1 General Electrically powered lighting should be used in tunnel construction. The selection and siting of luminaires should be in accordance with Clause 17 and should be such as to minimize the fire load. The design of tunnel lighting systems should take account of circuit length, extensions to circuit length, overload and short circuit protection along with automatic disconnection times.Lighting circuits should be separate from other sub-circuits and should be designed in accordance with the recommendations in 25.7. The preferred operating voltage for tunnel lighting should be reduced low-voltage 110 V single phase (see 25.7.2.3) or lower. Low-voltage 230 V single phase lighting should be used only when the lighting circuit is supplied from a fixed point and where the lighting fittings are fixed in positions out of normal reach and clear of danger of possible damage from foreseeable working operations.

23. Site electrical safety requirements(Arrangements)10. Lighting installationsLuminaires should have a protective enclosure that conforms to a rating of IP 55 in accordance with BS EN 60529:1992 where practicable. Where required, waterproofing and dustproofing of luminaries should be in accordance with BS6164 section 25.7.6. Where methane might foreseeably occur, explosion protected luminaries, typically rated Ex “e” or Ex “d”, should be used for underground locations. Luminaires operating at reduced low voltage but incorporating a step-up transformer should be used only in fixed positions and should be accessed by authorized persons only. Emergency lighting should be provided in accordance with BS6164 Section 17.5LuminairesAs per BSEN 16191: The lighting shall comply with EN 1837:1999+A1:2009. Working areas shall be illuminated to a level of at least 100 lux. Illumination at the level of an operator’s controls shall be adjustable up to at least 100 lux. The illumination shall be 30 lux at walkway level.

24. Site electrical safety requirements(Arrangements)11. Motors and generatorsTotally enclosed fan-cooled or liquid cooled motors in accordance with BS EN 60034-5 should be used. Open ventilated motors should not be used.Motors should be provided with overcurrent and single-phase protection and, in the case of HV motor starters, should additionally have instantaneous earth fault protection. Short circuit protection should be by high-breaking capacity motor rated fuses or moulded case circuit breakers where fault levels permit. Rewireable fuses should not be used because of their low fault-breaking capacity. Control circuits incorporating hand-held controls such as pendants should operate at a voltage not exceeding 50 V to earth. MotorsThe majority of TBMs are now fitted with programmable logic controllers, and care should be taken in the design of control circuits to ensure that safety is not compromised as a result of power failure or faults within the control system. Control circuits should be designed to be fail-safe to prevent a hazard occurring when power is lost or restored

25. Site electrical safety requirements(Arrangements)11. Motors and generatorsGeneratorsThere should be an interlock to stop parallel operation between the generator and the mains supply in accordance with BS 7430. There should be a robust system for ensuring that all consumables, including fuel, are always available. There should be a robust system for regularly maintaining and testing the generator. The generator should be ready to go on load immediately on start-up.Earthing of generators should be in accordance with BS 7430:2011,section 7.2All generators should have double skin fuel tanks or be set within suitably bunded locations.

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