Voltage Sensing Device Interlock 1

[nightfox1925]

Hi, I am conducting reviews on the design contractor's switchgear with separate earthing switches at their associated cable termination cubicle. I am looking on the interlocking scheme of these earth switches and noticed that part of the earth switch interlock is a "provision of a voltage sensing mechanism to inhibit earth switch closing if voltage is present on the cable". does this device exist in the market? If yes, may I request for any link related to it?

Respectfully....

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[davidbeach]

I don't know of a product.

But, define "if voltage is present on the cable". The whole purpose of a grounding switch would be to remove the voltage on the cable, so if you can't close the switch with voltage on the cable, when will you ever close the switch?

 

[nightfox1925]

I think this was specified for the purpose of safety to anyone who attempts (by accident) to close the earth switch if line voltage is present. I know that there is a capacitive voltage indicator fitted on the cable termination cubicle but not like it would act as an interlock. That made me wonder if such device is available.

On the other hand (for 11kV or 3.3KV nominal voltages), even if the cable supply voltage is disconnected, a voltage is still present in the cable due to stored capacitance.



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[dpmac]

I have seen many 5kV and 15kV installations where feeder voltage is monitored via potential transformers. Using an electric solenoid and a Kirk Key type interlock system, the ground switch can't be closed unless no line voltage is present. These type of set ups always seem rather hap hazard and almost always appear to be an after thought IMHO.

This type of set up is sometimes used to prevent electric operation of a Ground/Test device also. Saw some older Federal Pacific 15kV, 1200A, 1000MVA MC breakers use this set up to allow for actual electric racking in of the Ground/Test device into the cell.

Worked well enough until they blew a PT fuse and racked a closed G&T into the cell.

 

[nightfox1925]

Thanks dpmac, I may as well go for either an electrical or a mechanical interlock to safeguard switching the ground switch into a live line.

On the other hand, I will just suggest to place a capacitive voltage indicator at the cable termination cubicle.

respectfully...

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[jraef]

I asked a similar question some time ago. This is apparently a common requirement in MV systems outside of the US for those who don't know. I was doing projects going to the Middle East and this came up over and over. Here is my old thread.
thread279-121313
I never did find a source for them in the US, it just isn't done here and nobody understands it. We ended up using switchgear from the UK.

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[nightfox1925]

I will try to talk to the switchgear manufacturer and verify how they do it and whether the above mentioned interlock scheme is available.

Our client, wants to have both electrical and mechanical interlock separately for the same earth switch.

Thank you...

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[dewone]

Yes we do have these in the US. The equipment isn't US made but I have a customer with a simular set up in their High yard. 69 KV Siemens gear. Check with Siemens for info.

 

[nightfox1925]

Thanks dewsome, I will go to siemen's website and check it out. I already sent a query message to ABB.

Respectfully...

GO PLACIDLY, AMIDST THE NOISE AND HASTE-Desiderata