Load Tap Changer FP Type 25 RT32

While the LTC is in oil, we checked the transition continuity of the LTC, Make-Before-Break, using the Winding resistance tester. Based on the test result we found open circuit in the transition of the tap change. We flushed the oil, cleaned, and did some mechanical adjustement per the factory recommendation and fill the oil, tested again still we have the same problem.

Is there any way to check the continuity of the LTC without filling the oil. Using the WRT is a safety concern as the instrument injecting a minimun of 500mA and monitoring the current loop to detect open circuit. Since V=L(di/dt), for open circuit it will develop a high voltage.

Any suggestion would be appreciated.