LOW-VOLTAGE CIRCUIT BREAKER SELECTIVITY STUDIES

The article is devoted to the research of low-voltage circuit breaker (CB) series selectivity dependence on short circuit current and the manufacturer. The short circuit experimental tests were provided for three most widely used manufacturers' circuit breakers. Time-current curve classes B and C circuit breakers with current ratings of 16 A, 20 A, 25 A and 32 A were used. The research results prove that tripping times variate significantly between different manufacturers' circuit breakers - by 1.49-1.93 times. The circuit breaker series developed from one three-pole CB and one one-pole CB showed a possibility to provide total selectivity only at particular settings and moderate short circuit current. None of the CB series tested were able to provide total selectivity at high levels of short circuit current, just few of them showed partial selectivity. The research results prove that the use of different manufacturer MCBs in circuit breaker series connection needs to be analyzed carefully in order to provide selectivity and proper operation of the protection system.