Prestrike Characteristics of Vacuum Circuit Breakers with Cup-type AMF Contacts and Spiral-type TMF Contacts under Capacitive Making Operations

The objective of this paper is to investigate the prestrike characteristics of vacuum circuit breakers (VCBs) with cup-type AMF contacts and spiral-type TMF contacts during capacitive making operations, to determine which is better for capacitive switching. Two test groups are carried out. The waveform of the applied voltage, the inrush current and the travel curve of the moving contacts are measured. Before and after the capacitive making operations, the emission currents of each vacuum interrupter are measured. Special attention is given to the probabilistic distribution of the prestrike gaps, the inrush current interruption phenomena and the erosion caused by inrush current on contact surfaces. The results show that, compared with the cup-type AMF VCB, the spiral-type TMF VCB can significantly reduce the prestrike gap and the scatter in prestrike gaps, reduce the occurrence probabilities of the inrush current interruption phenomena and reduce the erosion on contact surfaces caused by the inrush currents.