Impact of multiple restrikes at vacuum circuit breakers on the EMC of medium voltage switchgear

Switching operations in the primary circuits of medium voltage switchgears are mostly attended by discharge processes in terms of pre- and restrikes between the switch contacts. Due to their high amplitudes as well as their steep wave fronts, such discharges are known to be very broadband and severe sources of electromagnetic disturbance. This contribution deals with the origin and the consequences of repetitively occurring electromagnetic disturbance pulses due to multiple restrikes at vacuum circuit breakers. On the basis of measurements at a special switchgear test setup, the impact of multiple restrikes at vacuum circuit breakers on the EMC of the switchgear installation is analyzed in time and frequency domain. Based on the results, the severity of multiple restrikes is estimated by comparing the disturbance values with conventional (well known) switching disturbances like during disconnector operations. Finally, some approaches for the handling of multiple restrikes at vacuum circuit breakers with respect to the EMC aspects are given in the summary.