Magnetic Signature of Vacuum Interrupters during Load Switching

The investigation of the circuit breaker's magnetic field emission provides fundamental data to estimate contact wear caused by the arc and perform magnetic field-based online monitoring of the switching operation of the circuit breaker. A synthetic test circuit is designed and built to measure the magnetic field emission when the vacuum circuit breaker interrupts an alternating current. The test circuit allows for adjusting the current amplitude, the contact separation time (arc initiating time), and the locations of magnetic field sensors. Fundamental characterization of the magnetic field emission before and after arc quenching and its correlation with arc current and voltage and circuit breaker operations are presented. Three characteristic magnetic-field waveforms (CMWs) appear in the magnetic field, and their causes are studied. Experiments confirm that these CMWs are strongly related to the abrupt change of the contact voltage, and their occurrences are synchronized with the opening and closing events of the vacuum interrupter and the arc extinction respectively. Based on this, a CMWs-based non-invasive method to detect contact erosion and circuit breaker operations is proposed.