Electromagnetic radiation from a circuit breaking action

It is well known that during the process of a switching action in circuit breakers an arc is initiated and drawn between two contacts. The occurrence of such an arc represents an excitation to the circuit breaker environment in the form of electromagnetic radiation. The initiation, propagation and electromagnetic field establishment of such switching induced radiations are important to understand the behaviour of electrical arcs as well as to aid possible implementation of EMC regulations in circuit breaker systems. In this contribution, experiments and simulation for a SF6 420 kV circuit breaker are reported. Measurements using both Rogowski coils indicate a radiation spectrum of up to 400 Mhz. It is also shown that by controlling the coil bandwidth it is possible to identify various important events during a circuit breaking action, such as initiation, contact separation, and current extinction. However because of the non-intrusive requirement required in a power system environment, these field measurements need to be conducted remotely and as such it is difficult to estimate the strength of radiation generated. To this end, the Transmission Line Matrix (TLM) method is employed to model numerically the initiation, propagation, accumulation of the generated electromagnetic radiation in the time domain. Based on a simple circuit breaker structure with conductive walls, the TLM simulation suggests significant radiation at 121.43 MHz and 314.29 Mhz. Comparison with experimental results shows a good agreement, thus permitting a viable and validated numerical estimate of the field strength within the circuit breaker structure. Practicalities such as non-conducting circuit breaker walls are then included in the computer model and the resultant simulation results are again compared with experimental results. Finally the TLM technique is assessed for its further application to circuit breakers.