Switching test of 35kV bridging regulation vacuum on-load tap changer

The 35kV bridging regulation on-load tap-changer (OLTC) is an important device to dynamically adjust voltage to ensure the power quality of the distribution network. The developed vacuum on-load tap-changer is a replacement to the oil arcextinguishing one with longer lifespan. Its switching process is critical to the quality of the tap-changer and the safety of the power grid. The article introduces the circuit that tests the switching process with load based on the resonance method and carries out the switching test with peak current of 200 A for the OLTC. It is found that 1.3pu overvoltage can be excited at the load side during switching. The floating potential part of the OLTC which may cause insulation failure during switching process is pointed out as the weak spot of the apparatus. The most dangerous moment for the insulation is analysed and the insulation withstand voltage during the switching process is evaluated by measurement. No significant transition overvoltage is observed due to the floating potential. The presented work validates the OTLC prototype and can be used as guide for future OLTC design and test.