A Study on the Characteristics and Breaking Performance Improvement in Small Current Region of a Low Voltage Direct Current Circuit Breaker

A low voltage direct current(DC) circuit breaker is an electrical protection device that interrupts the abnormal fault currents which result from the over-loads or short-circuits in a low voltage(less than 1,500Vdc) power distribution line. Recently, as interests in renewable energy fields(such as photovoltaic and energy storage systems) have increased, research on DC circuit breakers for system protection is also being actively conducted. However, breaking the fault current in DC system is considerably difficult even small current region since the DC does not have current zero point such as in AC. When a short circuit occurs, a fault current flows between contacts of a DC circuit breaker even though they are separated by the protective control system. Arc voltage between contacts of the circuit breaker should generate as high as possible during breaking phase. High arc voltage could lead the fault current of the circuit to zero so that arc plasma is eliminated. Based on this behavior, arc extinction system of a DC circuit breaker should be designed to effectively increase the arc voltage during current interruption period. In this paper, the characteristics of DC breaking specially in small current region were confirmed through several types of current breaking experiments and result analysis, and a method to improve performance of DC breaking in small current region was presented, and experiments were carried out to verify the validity of the method.