Overvoltage Protection of Thyristor in Bidirectional Hybrid Circuit Breaker

摘要

The overvoltage during the reverse recovery of the thyristor is the main cause of device damage, especially for the thyristor used under pulsed high current conditions. For thyristor components in bidirectional hybrid circuit breakers operating at medium voltage levels, this paper first builds a test loop to explore the impact of forward current peak value I_F and turning off di0_/dt_0 on tne reverse recovery process of the thyristor. The results show that under the condition of pulsed high current, the carriers stored in the PN junction of the thyristor have a saturation effect, and the peak value of the forward current I_F does not have a significant effect on the reverse recovery process. Turning off di_0/dt_0 is the main factor affecting the reverse recovery characteristics of the thyristor. On this basis, when the protection circuit adopts three different protection schemes: RC buffer, varistor and RC buffer + varistor, the voltage changes at both ends of the component during the reverse recovery process are calculated sequentially. Finally, a protection scheme using RC buffer + varistor can be obtained, which can effectively reduce the voltage rise rate at both ends of the component and achieve effective suppression of the over-voltage peak. It is an effective protection scheme under 10 kV medium voltage level pulse working conditions. Finally, a test circuit was built, and the on-off characteristics of the thyristor components during the short-circuit breaking process were verified to verify the effectiveness of the calculation analysis.