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Protection Riddle No.75 - CT Equipotential connection
What CT equipotential connection.  How it is connected?  Is there any length constraint, if so how much?
Author : Abdul Hameed
Mon, August 9th, 2010 - 18:59
The MV CTs can be supplied with round or rectangle window in the center. This provides easy installation for customer as they can use their primary cable or bus bar through the CT ID. Usually these CTs come with equi-potential shield around the ID surface. This equi-potential screen is attached with a pig tail (lead with connector) which comes out of the ID surface. This arrangement allows uniform distribution of charge (non-concentrated) around the surface which further ensures that the CTs withstand high current and high voltage environment in long term use.

Tue, August 10th, 2010 - 14:00
Thanks for quick reply.  Further to clarify let me know if there is any lenght constraints for this pig tail.  I think it should be connected to the live connection (bus bar in case bas bar CTs), in that case is there anything  like it should be connected the live connection with a short piece of lead, say 1m or something like that.  whether CT manufacturere specify this? 
Author : Abdul Hameed
Wed, August 11th, 2010 - 14:46
Manufacturer of medium voltage window type CTs usually use that equipotential screen ( above 12 KV) and related connection for equalize the potential of mentioned screen layer and live part of bus bars which is subjected current measuring to prevent the corona and it's hiss sound in switchgear. Therefore there are not any limitations for length of relevant pig tail. 
Author : Hamid - From: Iran
Sun, October 11th, 2015 - 10:24
Dear sir,
     Is it necessary to connect the equipotential wires to neutral side of alternator CT's.

I am awaiting for your reply sir.

Thanks & regards
Prasanna kumar 
Author : prasanna kumar - From: Indian
Tue, October 20th, 2015 - 09:50
No, never it should not be connected to neutral or earth bus. 
Author : Hamid - From: Iran
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