Influence of AC system fault on DC system control & protection and improvement schemes

Abstract

There are twelve high voltage direct current (HVDC) transmission projects in China Southern Power Grid. If the inverter alternating current (AC) system fault leads to HVDC protection system maloperation, it's harm to the safe and reliable operation of the system. To solve the above problem, firstly, this paper selects the possible maloperation DC protection functions on AC faults according to RTDS (Real Time Digital System) test. Then influence of AC fault on DC control protection is analyzed. Combined with the test and principle analysis, the improved idea of using AC system side protection to remove faults and avoid DC protection maloperation or blocking is put forward. It is suggested that the DC protection delay setting should be adjusted and matched with the AC protection setting within the main equipment tolerance, and the corresponding scheme of DC protection optimization is given. Finally, the simulation tests were carried out by the RTDS based on 7 HVDC current projects, and the improved protection schemes were verified. The improved protection schemes have been put into effect in China Southern Power Grid HVDC projects. The operation experience shows that these schemes can effectively avoid the shutdown risk of HVDC system caused by AC system fault.