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CT Primary Injection Ratio Testing Problems
Situation after CT Primary Injection:
New 230kv breaker
Testing CT’s, 4000/5, by high current injection
injecting 80 amps A phase to ground
the secondary leads are shorted in a junction box A-B-C-N / additionally a voltage is connected to test instrument form test set
The secondary readings are A = 0.096 @ 176 degrees, B = 0.01 @ 0, C = 0.01 @ 0, N = 0.108 @ 4
only one set of CT’s, 2 per phase read this all others tested where i.e. A=0@0, B=0.1@180, C=0@0, N=0.1@0When load was applied secondary current looked correct
Seems like I ‘ve seen this before, is there an answer for this?
Electricity is a Theory……………right?
sdg
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I’m not sure what the problem is. Are you saying A and B are switched?
Chris,
The A phase readings were not as expected.
They were not seeing the entire value on A and B&C small amount and the N was high
When testing the other phases the readings were full current on tested phase and N with zero on other phases
Kind of looks like the CT is not centered on the bushing or possible bad cable or some other interaction
Thoughts?
Steve
I don’t perform primary injection tests because the values always seemed to me to be small to be reliable. I can’t think of a theoretical reason why CT position compared to primary conductor should matter.
My gut tells me that you saw an induced current or ground current. Isolating the CT ground from ground for the test might make a difference.
Thanks Chris!
Yes the connection that they used through ground back to the test set is likely the issue
Steve