Controlled vacuum circuit breaker for transformer inrush current minimization

Random energization of unloaded transformers may produce large dynamic fluxes and cores saturation, which will result in magnetizing inrush currents with high magnitude. These inrush currents may cause a variety of undesirable effects in the system, such as improper operation of protective relays and fuses, mechanical damage to the transformer windings, and the degradation of power quality. Controlled transformer switching can eliminate these effects, and the optimal instant to energize the transformer is when the prospective flux induced by the source voltage is equal to the residual flux. In the present study, a 12 kV vacuum circuit breaker (VCB) with permanent magnet actuator for each pole was used as the transformer switch. A new type controller and adaptive compensation based on digital signal processor TMS320LF2407A was developed to the VCB. The transient process of unloaded transformer energizing was analyzed, and four control strategies of specified three-phase transformer were introduced. Experimental and simulation results prove that the hardware and algorithm are viable.