CT pase angle error.

[johndaniel]

I have 3CTs which are passing current signals to SEL351S relay. When I am measuring the current phasors in relay they are showing following values:
A B C N G
I MAG (A) 6.604 6.734 7.331 0.000 13.759
I ANG (DEG) 174.51 52.14 114.17 0.00 113.30

My Ia, Ib and Ic are not balanced. What could be the problem? is there any problem with CTs or with the connection of CTs?

Thanks

 

[davidbeach]

I strongly suspect that your C-phase current is going through the relay the wrong direction. Could be a wiring error at the CT, could be an wiring error at the relay, or anywhere in between.

 

[stevenal]

Or a wiring error within the CT. I know of one multi-ratio CT that checks out perfectly if you consider H1 to be non-polarity.

 

[rcw retired EE]

What David said.

Sketch the current phasors and you will see that C phase is 180 degrees from where you would expect it and the ground (residual) current is equal to twice C phase. Residual = A+B+C. For balanced currents A+B+C= 0 and A+B = -C. If C is backwards, A+B+(-C) = -2C.

 

[johndaniel]

Thank you all for your inputs. The problem was with phase C, CT connection. I rewired it and now it is working perfectly.