A Transformer Differential Relay Based on a Multiple Park Transformation

Discrimination between an internal fault and a magnetizing inrush current has been recognized as a power transformer protection problem, since can cause malfunction of a differential relay. To overcome this problem the paper proposes a new approach for transformer differential protection. This approach is based on the Park transformation of the differential currents. Using this technique each harmonic that must be used for the protection will be converted in a dc component. So, one of the advantages of this approach is that the proposed algorithm does not require a very high computational effort. The evaluation of this technique is performed by a Matlab/Simulink-based simulator. From the obtained results it is possible to verify that the relay can correctly discriminates magnetic inrush from an internal fault.