CT/PT/Secondary Ohms Question

[z06dustin]

Hi, if i have primary ohms, and I want secondary ohms, with a PTR of 600/1 and a CTR of 2000/5, how do I calculate that? I'm leaning towards Zprimary * (400/600). No?

 

[Flyer_PE]

^Impedance values translate by the square of the turns ratio. Are you trying to determine the impedance value on the secondary side of the PT or the CT?

 

[z06dustin]

^Impedance values translate by the square of the turns ratio. Are you trying to determine the impedance value on the secondary side of the PT or the CT?

Both. I'm doing a zone setting, lets say Zline = 1+j10 (pretend, for easy math). I want 80% of that for my Z1. But I want it on the secondary side.

 

[Flyer_PE]

The impedance seen by the distance relay will be: ZRelay = VRelay / IRelay

The easiest way I can think of to get there is to determine the fault current on the line with 80% of the impedance.

The impedance setting for the relay would then be the nominal voltage on the PT secondary divided by the current on the relay side of the CT.