Earthing of CT common at many points within CT loop 1

[Rakan Aljawabreh]

Dear Brother's,

I have 132KV CT with 6 cores, and the secondary connections is done as follow:

CT secondary box to Intermediate CT junction box to CT terminal at protection panel and then to Relay/Meters.

the question is where we have to earth the common of each core ( i.e 1S1, 2S1, 3S1, 4S1, 5S1, 6S1)???

 

[scottf]

Normal practice would be to use the highest # tap, meaning the "furthest" away from the polarity mark as the common terminal which is connected to earth/ground.

So, in your example, that would be 6S1. However, I think you might have written your terminal names wrong. In IEC, the format is 1S1-2S1, 1S2-2S2, etc... where the first number is the tap number and the last number is the number of the secondary winding/core.

 

[stevenal]

Per IEEE, the CT secondary is grounded at the first point of application. Of the locations listed, I would choose the CT terminal at the protection panel.