Research on DC component decay time constant of 1000 kV AC filter circuit breakers in UHV converter station

In hierarchically connected UHV DC projects, the 1000 kV AC filter sub-bank in converter station is provided with two 500 kV circuit breakers. To determine the test DC component decay time constant when breakers break short-circuit current, relevant DC project was modelled in electromagnetic transient program (EMTP) for calculations. It is pointed out that for UHV AC filter circuit breakers, the decay time constant of DC component of short-circuit current should be determined solely based on the single-phase to earth fault current. Calculations and analyses were made of the AC and DC components and the DC component decay time constant of filter single-phase to earth fault current, and the time constant calculated was converted to the test value of breakers with rated short-circuit breaking current of 63 kA. According to the research results, a time constant of 75 or 90 ms is recommended for the two 500 kV circuit breakers, and it is lower than 120 ms as required by the relevant standards, providing technical support for future breaker tests.