Earth Switch in Switch Gear Incomer

I am afraid that your question is not entirely clear. The word "Incomer" does not really define whether we are talk about a feed from a system transformer on a major switchboard, or a cable connected to a ring main unit in a local substation.

The purpose of Earthing Switches is to enable one to securely and safely earth a cable or transformer so that work can be carried out on it. You mention 11 kV, so the system is presumably based on UK practice, in which case the Earthing Switches will probably be fault making. The equipment makers label should enable you to confirm which standard is applicable to the equipment.

If you are referring to a major switchboard the arrangements for circuit-breakers in such a switchboard have changed significantly with time. Thirty years ago UK circuit-breakers would use oil for fault interruption, and be withdrawable. Then earthing was achieved either by :- (a) Fitting an earthing device on to the isolating contacts of the circuit-breaker. (b) Moving the circuit-breaker carriage to an alternative earthing position and earthing through the circuit-breaker (c) Fitting a special earthing switch in place of the withdrawn circuit-breaker. Since this time fixed circuit-breakers have been introduced using Vacuum and SF6 technology, and with this has come a number of different ways of providing the necessary earthing facilities.

The answer to understanding what has been provided is to carefully study the manufacturers literature.

John

The incomer I mean is, "a cable connected to a ring main unit in a local substation". Within a single board, we have an incomer, and 3 feeders. For every each feeder, they come with an integral earth switch, which is in place with vacuum circuit breaker.

The manufactures suggest having a earth switch at incomer side is not necessary and redundant. I am not sure whether it is true. Please advice.

Thank you very much.

In this situation it is up to you the operator to decide whether the switch is neccessary or not. The question is basically can you safely earth up the incoming cable to work on it at both ends ? If it is a radial system with no present or future possibilities of backfeeds, or if you are happy to havethe complete substation dead while you work on the cable, then maybe you can managewithout the earth switch, but I would argue that you should know how you would safely repair a fault in the incoming cable or cablebox.

John

I would have thought the supply authority would have insisted on a means of earthing the cable, for the safety of their own employees, and they would come in and ensure it was properly locked in place.

---< On Line using an Acorn StrongArm RiscPC >---

Same here :-)