New Synthetic Test Circuit for the Operational Test of HVDC Thyristor Valve

摘要

In general, the power handling capability of thyristors in the classical HVDC systems has seen significant progress in the past thirty years. It was known that five or more thyristor levels in a valve section should be tested for the adequate representation in case of valve section composed of twelve or more levels in series. This means that if we adopt the direct testing for the valve section or valve, we need very large testing power, which is not the practical solution. As a result, all HVDC valve manufactures are using synthetic testing method recommended by CIGRE as an alternative to the direct testing.Synthetic testing methods are based on the fact that the HVDC thyristor valve is stressed by current and voltage at different time intervals. The current stress occurs during the conduction interval followed by the voltage stress during the blocking interval of the valve. If we use two separate power sources, one voltage source and one current source, at different time intervals, it is possible to apply the voltage stress and the current stress to the test valve independently. This means that we can minimize the power required for valve test. Voltage and current stresses on a test thyristor valve can be analysed separately in four operation states: off-state and reverse voltage, turn-on, on-state and turn-off state. Key points of synthetic test circuit are how to control the transition intervals from one operation state to another operation state, critically from on-state to off-state or the opposite direction. This paper proposes a new STC (Synthetic Test Circuit) by adopting two-phase chopper with an auxiliary switching circuit for the turn-off of the “so-called isolation thyristor”. Also the proposed STC can minimize the power ratings of the current source equipment by supplying “the gate power of the test thyristors” through the resonant circuit side, not from the current source side. And the gate power of the thyristors in the resonant circuit is supplied through the independent high frequency power source. The proposed STC was tested under the requirement of IEC 9.3.1~9.3.3.