Primary current injection 138kV breaker with bushing CT's

[david2458]

I need to know how to conduct this type of test. I usually do secondary current injection, but I have the opportunity to do primary current injection using a CPC100. I will be testing CT's on a 138kV breaker with bushing CT's. I believe I need to connect the polarity side of the test lead to the bushing of the affected CT and the non-polarity lead to the other correlated bushing (i.e. if testing the ct for bushing one, polarity to it and non-polarity to bushing two), then short out the non-polarity ct's , ensure the breaker is closed, and push the current into the affected CT and verify correct magnitude and polarity at my relay. Don't mean to sound stupid, but I haven't done this test before. Thanks!

[ElectricalTestTech]

I need to know how to conduct this type of test. I usually do secondary current injection, but I have the opportunity to do primary current injection using a CPC100. I will be testing CT's on a 138kV breaker with bushing CT's. I believe I need to connect the polarity side of the test lead to the bushing of the affected CT and the non-polarity lead to the other correlated bushing (i.e. if testing the ct for bushing one, polarity to it and non-polarity to bushing two), then short out the non-polarity ct's , ensure the breaker is closed, and push the current into the affected CT and verify correct magnitude and polarity at my relay. Don't mean to sound stupid, but I haven't done this test before. Thanks!

The way I would approach it is by breaking it down to individual devices. I would Test the CT’s using whichever specs you’re required to follow (NETA or NERC or FERC). Test the breaker, test the associated relays. Then once every device has been tested and verified to be within tolerance, do a functional trip. Inject primary current through A-phase bushings and watch for a trip. If you already tested relays you should know what the secondary trio amperage will be; just convert it to primary and your trip should occur somewhere close to it. Repeat the steps with B and C phases.

This was a very dumbed down response. There are a lot of variables that were not explained. There are many ways to perform the testing. But my advice will always be, break down the system to individual components and test. Then follow through with a functional verification to ensure all wiring between devices are correct

I hope this helps