Power Transformer Inrush Current Detection & Harmonic Sharing In Differential Relay Protection
|International Journal of Engineering Trends and Technology (IJETT)||
|© 2016 by IJETT Journal|
|Year of Publication : 2016|
|Authors : J.O. Aibangbee
|DOI : 10.14445/22315381/IJETT-V33P206|
J.O. Aibangbee"Power Transformer Inrush Current Detection & Harmonic Sharing In Differential Relay Protection", International Journal of Engineering Trends and Technology (IJETT), V33(1),27-32 March 2016. ISSN:2231-5381. www.ijettjournal.org. published by seventh sense research group
Differential relays protection is one of the most widely used methods for protecting power transformer against internal faults. The technique is based on the measurement and comparison of currents at both sides of transformer primary and secondary lines. Security of transformer differential protection schemes is dependent on detecting the magnetizing inrush currents of the protected transformer and associated differential operation due to inrush was maintained for faults during inrush conditions, as the fundamental current in the faulted phase easily override the sum of the second harmonic currents associated with energizing the un-faulted phases. There is substantial DC offset to all three phases of both HV and LV side. Also, the B phase signal on the HV side, in particular, shows significant saturation. Evaluation of the signals internal to the relay shows typical fundamental unbalance current signals, but very low 2nd harmonic signals. By implementing harmonic sharing, a single harmonic signal was created. Each phase element of the differential relay uses this summed signal to make its independent restrain decision. With harmonic sharing, the overall percent harmonic signal is significantly higher. It permits fast tripping for all internal faults with minimal delay when energizing a faulted transformer, and prevent differential relay operation during transformer over excitation.
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MPBR, Differential Relay, Power Transformer, CTs, Inrush Current, Harmonic Sharing.