LC DC Circuit Breaker based on Pre-charged Capacitor Commutation

Abstract

To overcome limitations of the peak DC fault current with previous LC DC Circuit Breakers, this paper studies using a pre-charged capacitor in the auxiliary branch which enables rapid commutation of the fault current from the disconnector in the main branch. The analysis on the theoretical model concludes that the pre-charged capacitor should ideally have high capacitance and low voltage. The design for the practical test case of 5 kV, 2 kA LC DC Circuit Breaker is presented and shows that the pre-charged capacitor voltage requirement is low, at 10% of the DC CB rating. Both, film and electrolytic (lower size and cost) pre-charged capacitor are considered, and the experimental tests demonstrate successful DC current commutation of 2 kA at 5 kV. Successful breaking is also demonstrated on hardware for negative DC fault current and for very low currents, which represent difficult operating conditions. The experimental study further evaluates robustness to the change of timing of the current injection and the pre-charged capacitor voltage. The mechanical LC DC CB commutates DC fault current in very short time of 320 µs, and the use of pre-charged capacitor makes this topology good candidate for applications in medium voltage DC systems.