A Fault Current Limiting Hybrid DC Circuit Breaker

Due to the low impedance characteristic of the high voltage direct current(HVDC)grid,the fault current rises extremely fast after a DC-side fault occurs,and this phenomenon seriously endangers the safety of the HVDC grid.In order to suppress the rising speed of the fault current and reduce the current interruption requirements of the main breaker(MB),a fault current limiting hybrid DC circuit breaker(FCL-HCB)has been proposed in this paper,and it has the capability of bidirectional fault current limiting and fault current interruption.After the occurrence of the overcurrent in the HVDC grid,the current limiting circuit(CLC)of FCL-HCB is put into operation immediately,and whether the protected line is cut off or resumed to normal operation is decided according to the fault detection result.Compared with the traditional hybrid DC circuit breaker(HCB),the required number of semiconductor switches and the peak value of fault current after fault occurs are greatly reduced by adopting the proposed device.Extensive simulations also verify the effectiveness of the proposed FCL-HCB.

A Hybrid Circuit Breaker Based on Current Commutation Approach for Multi-feeder DC Railway Substations

The paper presents an economic hybrid circuit breaker for limiting and interrupting the faults in DC railways substations. For fast fault current interruption, the hybrid breaker incorporates high speed mechanical contacts actuated by power semiconductor devices. Additionally, to avoid formation of electric arc, a commutation circuit is used to inject a counter current during fault interruption. In a real railway substation, each feeder is connected to the main DC bus through an expensive air magnetic DC circuit breaker and to an auxiliary DC bus through another expensive breaker. This leads to high cost especially in railway substation with multi feeders which are used to energize the vehicle transmission lines. In this paper, all DC breakers in DC railway substations are replaced by the suggested circuit breaker, which consists of a high speed mechanical contact with two semiconductor devices in each feeder and only one commutation circuit for injecting the counter current in all faulted feeders. The fault diagnosis is designed to detect the abnormal condition (current or voltage) in all feeders and direct the injected current from the commutation circuit to the faulted feeder only when the abnormal reaches a predetermine level. The suggested breaker is able to detect and interrupt any cascading of faults.