MEW Specifications

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7.

8.

Proper control wiring identification ferrules ( sleeve type ) shall be provided at both ends of the control wiring. The wiring terminal shall be numbered with ring ferrules in such a manner that if a wire is connected between terminal block x2.6 and relay e5.3, then the wire terminal at x2 should read e5.3 and the wire terminal at e5 should read x2.6. This system shall be strictly adopted in preparation of drawings as well as various panels for easy tracing of the wiring. It is clarified that equipment and transformer tap change are not required to be ferruling of back to back system. However external wiring should follow back to back ferruling system. All tripping relays located inside local control panels and relay panels which can cause tripping if touched accidently during maintenance shall be provided with additional safety covers, which, when necessary can be removed in case any testing or maintenance is to be carried out on these relays. In addition to this, a prominent and suitably worded caution label should be provided. The maximum operating time allowed for tripping relays is 10ms. An evidence of suitability of the proposed relay/contactor to safe operation (i.e. no false tripping due to mechanical shock and vibration) has to be submitted. These tripping relays/contactors must be manufactured and tested in accordance with the IEC 255 (4 & 5) and BSS 142, 5992 as applicable.

6.7.15 Pilot Cable Supervision: (For 132kV & 33kV Systems) For pilot cable supervision, high frequency guard tone used with inter-tripping equipment shall be utilized. The loss of this tone shall be transmitted to the control centre and shall mean either inter-tripping equipment faulty or pilot cable faulty. To avoid occurrence of flash-over across the terminals in the marshalling cabinet, tenderers are requested to provide the necessary protective measures for terminal equipment as well as the operation staff against induced voltage due to phase-to-ground faults on the associated power cables. For all pilot cable cores other than Solkor (RF) cores suitably rated surge arrestors approved by the purchaser shall be installed for protection of terminal equipment and operating personnel. These surge arrestors are preferably installed in a separate panel located adjacent to the marshalling cabinet. On the other hand the terminal blocks in the M/C, control cabling to control room and inter-tripping relays for the far end substation (where applicable) shall be insulated for at least 5kV & 15kV, for 33kV and 132kV systems respectively. The cost of supply and erection of the above shall be included in the tender price, however, the arrangement shall be subject to the Purchaser’s approval.