A controlled switching methodology for transformer inrush current elimination: Theory and experimental validation

Transformers are generally energized by closing the circuit breakers at random times. Consequently, this operation generates high transient inrush currents as a result of the asymmetrical magnetic flux produced in the windings. In light of these facts, this paper presents a strategy to control the switching phenomena which occurs during power transformer inrush. The general idea consists of calculating the pre-existing magnetic fluxes left on the core limbs as a function of operating voltage previously applied to the transformer, just prior to the moment in which de-energization has happened. By using these data and the equations to predict the most suitable closing moments, it is shown the proposal effectiveness at accomplishing the main target here pointed out. Experimental investigations are carried out in order to demonstrate the application method and its validation. The results show the feasibility of building hardware and software structures to drastically reduce the transformer inrush currents.