Study on Non-periodic Firing Test Technique for ETT Thyristor Valves

With the increasing demand for electricity and the rapidly development of electric power techniques, HVDC techniques has been widely used. As one of the critical facilities in HVDC system, thyristor valve has to be strictly tested to verify its´ dielectric performances before used. Non-periodic firing test is an important one in all dielectric type tests of thyristor valve. The test verifies the valve´s ability of enduring large impulse current with thousands of ampere under rated switching impulse voltage. This paper introduces a method for non-periodic firing test, which takes ETT structure as an example. Firstly, the equivalent circuit of ETT structure is set up. Parallel capacitor method is used to perform the test using the simulation results of test parameters obtained by PSCAD. An simulation model for the test circuit is also introduced and the actual test circuit diagram is presented. In addition, we discuss the logical sequence of various control signals, compare the impulse current measured by diverter and rogowski coil and analyze the influence on the two measuring devices from earthing condition during test. Finally, an accurate method of measuring impulse current is proposed. The waveforms of the test are listed at the end of the paper. The comparison between test results and simulation results prove that it is feasible to obtain test parameters by using PSCAD in non-periodic firing test for thyrisor valve.