Abstract: Conventional dielectric loss tests for coupling capacitor often yield values that exceed the standards. After analysis and verification, it is found that the Garton effect of the insulating medium inside the capacitors is the main reason for the abnormal dielectric loss at low voltage, which cannot reflect the real insulation defect inside the capacitor. Through the high-voltage dielectric loss test, it could be observed that the dielectric loss value of the capacitors changes regularly with increasing test voltage. When the voltage drops back to 10kV, compared with initial values, the dielectric loss values decreased significantly. In this method, the influence of the Garton effect on the actual dielectric loss value has been reduced, which also provides an effective basis for judging whether there is a real insulation abnormality in the breaker capacitance.

Key words: coupling capacitor, insulation tests, high voltage dielectric loss, Garton effect