Testing of differential relay operation for power transformers protection using RTDS

The work reported in this paper demonstrates the use of Real Time Digital Simulator (RTDS) for testing of differential relay operation in the protection scheme for power transformer. The RTDS simulator enables real-time calculation of the electromagnetic phenomena with the calculation time step of even 50μs. The hardware enables import and export of many signals from the simulator to an external actual power transformer and other components in power systems and therefore the so-called closed-loop testing. In this way, it is possible to have an insight both into the components behavior and also into the impact of this component on the power-system operation. Testing of discrimination among magnetizing inrush and internal fault currents is described. The obtained test results are shown proving usefulness of the RTDS simulator for determination of the actual power transformer behavior at various power-system conditions. The RTDS software i.e., RSCAD is used for simulation of power transformer and power systems model.