Multibreak LC DC Circuit Breaker

Abstract

LC DC Circuit breaker has previously demonstrated great potential for applications with DC grids at high or medium voltage, and this paper presents further technology improvements based on an experimental study. The increase in the arc voltage is analysed as the number of break points increases, since arc voltage critically determines magnitude of DC current that can be commutated. The paper describes the design of a 4-break contact assembly which provides total air gap of around 6 mm. It is concluded that it is feasible to build a 4-break disconnector with a 5 m/s gap velocity and with around 30-40 µs tolerance in the opening time of the four breaks. The experiments show that each break point increases the gap voltage and the commutating current almost proportionally to the number of break points. The measurements confirm that 4-break LC DC Circuit Breaker using 800 µF capacitor can commutate 930 A DC current with around 4.2 kV recovery voltage. It is measured that the commutation occurs 290 µs after the trip signal, which also denotes the time when DC CB begins inserting increasing counter voltage, and which is faster than most commercial DC breakers.