Residual Magnetic Flux of Three-Phase Three-Leg Transformer for Controlled Switching

When transformer is being energized, a large magnetizing inrush current flows depending upon the closing phase of circuit breakers and the residual magnetic flux in the iron core. One of the suppressing the magnetizing inrush current method is to control closing phase of the circuit breaker. For the controlled switching, it is very important to know the residual flux after the transformer was interrupted. So far the residual magnetic flux for the three-phase three-leg transformer has not been discussed. In this paper, the residual magnetic flux of a three-phase three-leg core type transformer is discussed by simulation and actual measurement. The residual magnetic flux for three-leg transformer is clear. It is shown that the controlled switching for three-phase three-leg transformer is able to apply.