Experiment of Semiconductor Breaker using Series-Connected IEGTs for Hybrid DCCB

This paper considered application of series-connected press pack Injection Enhanced Gate Transistors (IEGTs) as a semiconductor breaker for hybrid DC circuit breakers (DCCBs) of multi-terminal HVDC transmission systems. In order to interrupt a large current equivalent to fault current without parallel connection of press pack IEGT, the snubber circuit was applied. With the snubber circuit, surge voltages and switching losses can be reduced. Therefore, IEGTs can interrupt lager currents with the snubber circuit. In order to balance voltages across each series-connected IEGT, each IEGT should be selected to have similar properties. The circuit condition and operation timing of each IEGT should be adjusted. In order to confirm the capability of the proposed configuration, a prototype of hybrid DCCB was demonstrated. The semiconductor breaker of hybrid DCCB prototype was composed of four series connected IEGTs (4.5 kV, 2.1 kA) with the snubber circuit. Experimental result shows it successfully interrupted the current of 9 kA. Furthermore, the peak voltage across the semiconductor breaker was 14 kV. Variation of the voltage across each IEGT was less than 5 %. This means each IEGT peak voltage was suppressed under the withstand voltage of IEGT.