Research on the HVDC Operation Mode with Defective On-Load Tap-Changer

The on-load tap changer(OLTC) is used in HVDC system to make sure the AC voltage or firing angle in an appropriate range. In recent years, after a number of onload tap-changer failures, many OLTCs of the same type were checked, and it was found that due to cracks and other conditions, the remaining action times of some still-operable OLTCs were far less than the theoretical action times. Due to production cycle and other reasons, defective components cannot be replaced in time. This requires that the DC system should be operated with a defective OLTCs. This article proposes several temporary operation measures: extend the interval between OLTC actions, adjust the OLTC control mode to Udi0, and avoid 70% voltage drop restart conditions. Using these temporary operation measures can effectively reduce the number of OLTC actions and extend its life, while ensuring the safe operation of the HVDC system. Simulation analysis proves the effectiveness of the scheme. This scheme has been implemented at the actual HVDC project site.