Calculation of Turn-On Stresses In a Hvdc Valve Having Parallel Thyristor Strings

A computer model is used to demonstrate the turnon stresses of thyristors connected in series and for paralleled thyristor strings within a HVdc valve. The performance of parallel strings is compared with single strings of directly paralleled thyristors. The use of inductors in the strings is considered, and the possible benefits of controlling relative gating instants of the thyristors are analysed.