Parallel Current-Sharing Characteristics of Vacuum Multi-Breakers for Large-Capacity Generator Circuit Breakers

The rated current and short-circuit current of the large-capacity generator circuit breaker (GCB) far exceed the limit of a single vacuum circuit breaker (VCB). In this paper, a large-capacity GCB scheme based on multiple VCBs in parallel was proposed, focusing on the parallel current-sharing characteristics. Firstly, the current-sharing path and current transfer path were clarified, and a complete and specific circuit model was established. Secondly, the product variability of the vacuum interrupter (VI) and the action dispersion of the operating mechanism would cause the "current unbalance" problem. The influence rule of impedance matching, arc voltage, arcing synchronization, and other factors on the current-sharing characteristics was studied in detail, and the method that can effectively improve the static and dynamic current-sharing was proposed. In addition, the phase-to-phase electromagnetic field would cause the current of each VI in single-phase GCB to have an obvious phase difference, which greatly reduced the current-sharing effect. The electromagnetic shielding shell (ESS) installed on the GCB could effectively shield the external electromagnetic field and significantly improve the current-sharing effect. The improved ESS significantly reduced phase-to-phase magnetic leakage and avoided magnetic field pollution. Finally, the current-sharing experiment of the prototype proved that the proposed scheme could achieve a better parallel current-sharing effect, which may initially solve the problem of the insufficient current carrying capacity of the VCB.