The Analysis Of Commutation Failure Prediction In UHVDC System

Commutation failure is a common fault in UHVDC system. Last year, there were 15 commutation failures in Suzhou Station. To deal with this problem, every inverter station has commutation failure prediction in control system. Commutation failure prediction is a way that can adjust the control strategy of HVDC to avoid commutation failure. In Suzhou station this function is mainly through the monitoring of AC voltage to adjust the firing angle, avoiding extinction angle decrease. But adjusting the firing angle may reduce the DC voltage which means DC power drop. In Suzhou station, the breakers of AC Filters lack of stability while closing. So connecting an AC Filter can cause UAC disturbance and then make the commutation failure prediction to function and the DC power drop immediately. This thesis shows several existing commutation failure prediction method and analysis about fault recorder of commutation failure and commutation failure prediction. Based on the data in Suzhou station, a possible improvement to commutation failure prediction is presented. By modifying the logic, it can avoid commutation failure prediction functions frequently so that power quality is guaranteed.