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Calculation of overvoltage distribution in HVDC thyristor valves

Thyristor valves are the core components in HVDC transmission system. These valves in the system are exposed to various overvoltages both external and internal. So it is important to analyze the characteristic of the converter valves under different overvoltages. Wide-band equivalent circuits of the valve components such as thyristor, saturable reactor are obtained based on impedance measurement. And stray capacitances of valve sections in valve tower are included in these wideband models. Based on these models, overvoltage distributions in the valve tower are calculated and analyzed under different kinds of surges, including switching, lightning and fast front. To illustrate the effects of shielding plate, three different cases are calculated and analyzed. And some useful conclusions are presented in this paper.