Analysis on method of calculating transformer residual flux by using the integration of port-voltage waveform and its implementation

Inrush current caused by residual flux is the main reason that makes transformers fail to be re-energized. The concept of calculating transformer residual flux by the integration of the port-voltage after de-energization was proposed previously. In this paper, the principle of the concept is analyzed using phasor method. The concrete implementation is put forward, including two methods of determining the time limit of the integration. To verify the integration method, the transformer voltage waveforms are simulated under different hysteresis loops of core by the software Simulink. The method can provide more accurate results of residual flux after de-energization, improving the accuracy of the method of residual flux calculation.