Case study # 2.9 Title Malfunction of circuit breaker due to lightning surges Type of trouble Abnormal operation. Source of trouble Lightning. System affected Access system. Location Outdoors. Keywords Safety, immunity, lightning, power transmission line, circuit breaker, MOV. Version date 2004-01-01 System configuration The circuit breakers in the power units of an access network system located outdoors malfunctioned due to lightning. The access network system had an optical fibre cable, which was connected to centre equipment, a metallic subscriber cable, and an AC mains line (Figure 2.9-1). The system had four power units. Each unit had a circuit breaker, with a capacitance of 5 A at the AC mains frequency. Figure 2.9-2 shows the system's protection circuits. The power units are produced by two manufacturers. Their circuits were almost the same, but they had different malfunction occurrence probabilities. Miti(08)_F2.9-1 Figure 2.9-1 – Access network system Miti(08)_F2.9-2 Figure 2.9-2 – Structure of overvoltage and overcurrent protection Copyright © ITU 2010 – All Rights Reserved