Effect of CCVT Gap Protection Circuit on Voltage Distortion

Long-term voltage records of coupling capacitor voltage transformers (CCVTs) indicate that CCVT voltage is occasionally distorted under normal operating conditions. Serious voltage distortion in CCVTs can cause the protection relay to trigger a circuit breaker (CB). This work analyzes the reasons accounting for voltage distortion of CCVTs and the impact of voltage distortion due to deterioration of gap insulation in CCVTs. In this work, the CCVT parameters are measured by using an LCR meter in a power laboratory. The electromagnetic transients program/alternative transients program software is used to establish a CCVT model. Finally, the simulating results are compared with the test records to confirm that voltage distortion is caused by an instantaneous short-circuit fault in the CCVT gap. Additionally, simulation analysis confirms that a permanent short-circuit fault at the gap burns the damping resistor in the CCVT, and the protection relay warns of a burden voltage drop at the secondary side of the potential transformer.