Lc Dc Circuit Breaker Based on Pre-Charged Capacitor Commutation

The article presents study of a medium-voltage LC DC Circuit Breaker with pre-charged capacitor. The pre-charged capacitor is located in the auxiliary branch and enables rapid current reduction in the disconnector in the main branch. The analysis of the theoretical model concludes that the capacitance of the pre-charged capacitor should be high and the voltage should be low for the optimal design. 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 below 10% of the DC CB rating. The experimental tests are performed using both film and electrolytic pre-charged capacitor and 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. 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