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Security Enhancement of Differential Protection of Power Transformers Based on Second Order Harmonics

Usama Khaled1, 2, Mohamed Qais1, Saad Alghuwainem1 and Abderrahmane Beroual3

1. Department of Electrical Engineering, King Saud University, Riyadh 11421, Saudi Arabia

2. Department of Electrical Engineering, Aswan University, Aswan 81528, Egypt

3. Ampere CNRS UMR, Ecole Centrale de Lyon, Ecully 69134, France


Abstract: Differential relays are designed to protect the PTs (power transformers) from total damage when faults occur inside the PTs. Differential protection security of PTs is affected by external disturbances such as inrush currents, external faults, and over-excitation which cause undesired PT outage. In this work, a reliable algorithm is presented to improve the speed and security of PT protection. FFT (fast Fourier transform) method is used for taking out the second order harmonic of measured currents by CTs (current transformers) of the primary side and secondary side of PTs. The algorithm produces two signals: operating signal to disconnect PT during internal faults; and restraint signal to block the undesired action of the differential relay through external disturbances. The algorithm is inspected using PSCAD/EMTDC, where various abnormal conditions internal faults and external disturbances are simulated. The achieved results reveal that the proposed algorithm enhanced the speed and security of differential relay with simplest signal processing method compared to other techniques.

Key words: Security, Enhancement, of, Differential, Protection, of, Power, Transformers, Based, on, Second, Order, Harmonics
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