Origin of the Damped Oscillatory Waves in the MV Mains of the High Current Testing Laboratory

The High Current Testing Laboratory (HCTL) must be safe for the operational staff. Moreover, the equipment supervising the test must operate without any malfunctions. Relevant elements of the setup in the HCTLs are a three-phase 15 kV supply source, a medium voltage (MV) circuit breaker (CB), a three-phase supply line, a medium voltage/low voltage (MV/LV) transformer and a short circuit switch in the circuit at the secondary side of the transformer. The time-phase controller used for supervising the test in the HCTL under consideration is observed to get sporadically out of control by switching ON the MV CB. Unexpectedly, it starts the test immediately, i.e., it closes the short circuit switch without the operator’s release. It was reported in previous publications of the authors that repetitive Damped Oscillatory Waves (DOW) cause malfunctioning of the time-phase controller. However, answering the question about the origin of the DOWs and the number of DOWs is elaborated only in this paper, using numerical simulation of the transients in the MV supply line. In the paper, a numerical model of the three-phase circuit is presented. Transients that follow closing of the MW CB are simulated. Numerical simulations confirm that the origin of DOWs is the closing of the MV CB, and the repetition of DOW is due to different instances of closing the switch in each phase.