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Grounding switches in Gas Insulated Metal Enclosed switchgear

Grounding switches in Gas Insulated Metal Enclosed switchgear

Grounding switches in Gas Insulated Metal Enclosed switchgear


One client is requesting for the incomer of a MV gas insulated metal enclosed switchgear (arc resistant), to include two grounding switches: one in the incoming cable connection side and another one being the usual 3-position-disconnector/grounding switch that is located between the circuit breaker and the busbar. Being the circuit breaker non-withdrawable because of the SF6 gas insulation of the cubicle, I see no point in this additional grounding switch in the cable connection side. I have been checking different manufacturers and have not been able to locate anyone offering this.

Someone came across the same requirement? Which would be the purpose? Because with the circuit breaker of the fixed type and no maintenance required, I cannot see any advantange of including this grounding switch. Is this any standard requirement in ANSI/NEMA/UL/IEEE world? Something in NESC or NFPA 70E? Some utility practice, perhaps?

Best regards, radug.

RE: Grounding switches in Gas Insulated Metal Enclosed switchgear

The grounding switch on busbar side of the CB is used to ground the cable (with Disconnector towards busbar open).
The sequence would be - Open the CB, Turn the three position switch to Ground, Close the CB.
The grounding switch on cable side is meant to ground the busbar whenever required and is interlocked with all the feeder Disconnector switches (Open status) which means the incomer Grounding switch cannot be closed unless the Disconnectors of all feeders are open. Grounding the busbar is again done through the Circuit Breaker.
I have seen this practice in Shell standards.

RE: Grounding switches in Gas Insulated Metal Enclosed switchgear

Hi RRaghunath,

We also have a busbar grounding switch. Besides, I am not getting your point. The cable side grounding switch is farther than the CB side switch-disconnector, so it would not be able to ground the busbar.
Refer to attached image. Busbar is in the top and I am referring to the disconnector+grounding switch in red.

RE: Grounding switches in Gas Insulated Metal Enclosed switchgear

Looking at the picture you are right the three position switch on cable side seems redundant.
This switch, the way it is connected, cannot be used to ground the busbar.

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