Influence of Reverse Recovery Time on In-situ Protective Test of Thyristor Level in the Converter Valve of HVDC Power Transmission

The converter valve's electrical performance has a direct effect on the reliability, stability and efficiency of the whole HVDC transmission power system. The thyristor level is the basic unit of the converter valve, and each thyristor level in the converter valve needs to be test routinely during the maintenance period of the electric equipment. The protective firing test is an important part of in-situ electrical test of thyristor level in converter valve. In the paper, the reverse recovery experimental platform of high power thyristor was built and the effects of forward current amplitude on reverse recovery characteristics of thyristor were studied under the power frequency. Results show that the reverse recovery time increases exponentially with rise of the forward current and tends to be saturated, and its saturation value is about trr≈1020μs. The in-situ protective trigger function test of thyristor control unit (TCU) is closely related to maximum value of the thyristor reverse recovery time. According to the reverse recovery time of thyristor, the impact time parameter of the transient test pulse output by the impulse power supply in synthetic test system of thyristor level is set to test the TCU protective trigger function. For low-voltage protective firing test in the thyristor reverse recovery period, the low voltage pulse should be output to thyristor level at the time of trr+50μs (1070μs); for high-voltage protective firing test in the thyristor reverse recovery period, the high voltage transient pulse should be output to thyristor level at the time of 1.2trr(1224μs). Results of the TCU protective firing test show that the time parameter setting of the test pulse is effective and reasonable.