Earth switch in incomer

[paliha]

I have seen earth switch (ES) on the 33kV incomer cubicle of the switchgear. It may be a requirement for the supply authority to ensure no power will be fed back during maintenance etc. My question is how to provide interlock to ensure the ES will not be operated while incoming supply is present. Any clarification?

 

[thermionic1]

You can have electrical, mechanical (or both) interlocking. Electrical might include 'b' contacts from the disconnect and breaker. Mechanical might be something like a kirk key interlock system.

 

[crshears]

OP seems to be inquiring about an earthing switch on the supply side of the disconnect switch.

If that is indeed the case I fail to see what type of mechanical interlock would prohibit ES operation if potential is present.

Is there is some sort of existing and certified device with a potential sensor that would hold an interlock key captive while live?

Even if there is, and I've never heard of such a thing, I'd be concerned it could be defeated if any of its protective fuses would blow . . .

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[paliha]

I am sorry the attachment was not included. Please have a look now.

 

[crshears]

For me, that muddies the waters even further . . .

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[RRaghunath]

In case of transformer incomers in a plant, the incomer earth switch is interlocked with the circuit breaker (DS is preferred if available) on the primary side of transformer so that the earth switch cannot be closed unless the upstream transformer primary circuit breaker / Disconnecting Switch is open. Further, the incomer earth switch is also interlocked with a no-volt relay to ensure that the incomer is dead before Earth switch is closed.
Now, you can look in to the possibilities at your end.
I guess since there is an incomer VT, no-volt interlock should be easy.

 

[paliha]

Incoming supply is from city power. So electrical interlock is also not possible. Only option may be to used DS with earth position. Appreciate your response.

 

[RRaghunath]

paliha, I do think Electrical interlock is possible as there will surely be a VT in your premises.
If yes, it is only a matter of extending that VT signal to a No-volt relay.

 

[bacon4life]

Having the grounding switch interlocked with a disconnecting switch seems much more secure than relying loss of voltage. In my region the worker safety rules require a visible isolation point, so having an incoming disconnect switch is common.

 

[davidbeach]

Incoming disconnect and the ground switch on the receiving side of the incoming disconnect and the two mechanically interlocked such that the ground switch can only be closed with the disconnect open and the disconnect can only be closed with the ground switch open. Backward of traditional line grounding switches (ground the line, not the gear) but customers never get to ground the line.

But, why? Other than on GIS installations we've been removing ground switches rather than adding them. Crew applied personal protective grounds are a better approach. Grounding both ends of a line of any length, or with any mutual coupling, can result in nasty surprises. And don't get me started on customers who have ground switches and don't know that they have to be open before energizing...

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[desertfox]

Hi paliha

To my knowledge the ES is interlocked with the main switch within the same cubicle as stated by others, however I have previously designed earth switches for making onto a fault and a fault rated withstand time for the case you describe, that said some form of key interlocking or similar should be possible. If not the protection on the supply breaker should cut the supply off in the event of an earth fault.

Have a look at this site it might help :-

https://www.slideshare.net/Bryan_ZA/interlocking-on-switchgear-principles

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein