Checking or Testing of 33 KV Aircore Reactor of Filter bank circuit as it is tripping by Thermal pro

[afzumannu]

Dear All,
We Have 33 KV filter bank circuit for Compensation plant which include Line CT, Reactor and capacitors bank, we are facing trouble as this one phase circuit is tripping with Thermal protection and others are Ok, reactor value 11.85mH, Line CT 1000/1, Unbalance CT 10/5 CPR-04 relay is used for Protection, CT checked it's fine, Capacitors bank checked it's fine too, all the balance value and similar, capacitor in double star connection. We have doubt in reactor unit as it producing abnormal sound as we have noticed during switching ON,we dont have any testing kit for its mH value checking or any other test, can somebody help me out that how to test or check this reactor by simple method that it is ok or not? I am attaching SLD of one phase.

 

[afzumannu]

Please consider the Attachment first Slide only

 

[unclebob]

How your thermal protection works? Could be a faulty thermistor or RTD?
Is the abnormal sound only appears when switching ON?

As for testing, the only tests that come to mind are: Megger, Winding Resistance and Doble, or PF test. I think the Doble test can measure a Inductance value.

 

[RRaghunath]

I suspect setting for thermal overload protection.
CPR-04 literature provides an example calculation for setting different parameters of the relay. Hope you followed the setting recommendation! Some protection engineers have a tendency to provide sensitive settings thinking it is good for the equipment.
Verify the basis/correctness of heating / cooling time constant set, especially.
If you are sure of the correctness of the setting, it could be the problem of harmonics in the system. The harmonics are known to overload the capacitors.
From your sketch the capacitor is part of a 3rd harmonic filter. It could be that the actual 3rd harmonic quantity is more than that considered in filter design or it could be some other harmonics are finding their ay in to the filter, overloading it. Did you measure the harmonics and check against the design value?
One thing I am sure is that it is not fault in reactor or capacitor that is causing the overload trip. A faulty reactor/capacitor is likely to cause overcurrent or earth fault trip and not overload trip.