Optimal gang-operated switching for transformer inrush current reduction

•Optimal instant for simultaneous closing strategy to reduce transformer inrush current is proposed.•Independent-pole-operated circuit breaker is not required.•Optimal switching instant is analytically obtained.•The method has been tested in ATP/EMTP simulations and the expected results have been obtained.•Simulations considering the effect of circuit breaker pre-arcing have shown a higher reduction of the inrush current.

Controlled switching technology with independent-pole-operated circuit breakers is an effective way to eliminate transient transformer inrush currents. This technique cannot usually be applied at lower voltage levels where three-pole-operated circuit breakers are more frequent. In this paper, the optimal instant for a simultaneous closing is obtained as a solution of a min–max problem. The proposed strategy has been evaluated in a test system using EMTP/ATP and has presented highly satisfactory results, even when actual characteristics of circuit breakers are taken into account.