Shunt Reactor CT Ratio Testing Error
Shunt Reactor CT Ratio Testing Error
(OP)
Hello,
We are commissioning our first 345kV shunt reactor and are finding 15% error in measured CT ratio tests on all bushing CTs.
Manufacturer states that when tested outside of the bushing, all CTs were good, but their testing when CTs were mounted showed same results we are getting. I am waiting for their test results.
345kV shunt reactor, 3ph, 40MVar
2CTs/bushing, 2000:5MR C800, Y-connected, connected and tested at full ratio.
Tests showing 347/1 ratio rather than 400/1.
Testing being performed at the reactor with secondary circuits disconnected, voltage method, shorting leads on bushings not under test, similar to when we test transformer CTs.
I think it has something to do with the reactance, similar to a transformer without shorting leads applied, but can't quite work it out. Has anyone seen this and know the why? I will have to brush up on some theory when I get home.
Thanks.
We are commissioning our first 345kV shunt reactor and are finding 15% error in measured CT ratio tests on all bushing CTs.
Manufacturer states that when tested outside of the bushing, all CTs were good, but their testing when CTs were mounted showed same results we are getting. I am waiting for their test results.
345kV shunt reactor, 3ph, 40MVar
2CTs/bushing, 2000:5MR C800, Y-connected, connected and tested at full ratio.
Tests showing 347/1 ratio rather than 400/1.
Testing being performed at the reactor with secondary circuits disconnected, voltage method, shorting leads on bushings not under test, similar to when we test transformer CTs.
I think it has something to do with the reactance, similar to a transformer without shorting leads applied, but can't quite work it out. Has anyone seen this and know the why? I will have to brush up on some theory when I get home.
Thanks.






RE: Shunt Reactor CT Ratio Testing Error
Do you have the ability to see the volts, amps and phase angle from your test equipment? Is the ratio error consistent at different test voltages? Have you performed excitation test prior to ratio test?
RE: Shunt Reactor CT Ratio Testing Error
RE: Shunt Reactor CT Ratio Testing Error
Have you tried testing with the other bushing not shorted, but not connected to the line?
RE: Shunt Reactor CT Ratio Testing Error
Have you grounded the shorted bushings (not under test)?
I've seen results similar to yours in Auto Transformers with a delta tertiary and generally it is resolved via shorting and grounding.
RE: Shunt Reactor CT Ratio Testing Error
First tests were done with ground bar disconnected from neutral side on the phase under test (H03 terminal) and H1, H2, H3 terminals had no trainers connected. Error existed.
Same configuration but with H01, H02, H03 terminals all shorted and grounded, same CT ratio error.
Same configuration with neutral ground removed, error existed.
We were thinking of the reactor as an auto-transformer with no low-side tap and testing it as such. This is an oil-cooled, coreless reactor.
RE: Shunt Reactor CT Ratio Testing Error