Use of higher harmonics in currents and voltages for phase-to-ground fault protection in medium voltage networks

Directional single-phase earth faults protection has been developed for medium voltage (6–35 kV) electrical networks, operating with a neutral isolated or grounded through a Petersen coil. The principle of protection is based on determining the sign of the total reactive power of higher harmonics obtained after the discrete Fourier transform of the measured currents and voltages of zero-sequence and their numerically found derivatives. The results of mathematical modeling show that when the phase is grounded during the period of the fundamental frequency, due to recharging of phase capacitors in currents and zero-sequence voltages, higher harmonics occur, the amplitudes of which are second to tenth compared to the first and can be used for protection. The algorithm of the laboratory sample of protection is developed and positive results of its work at mathematical modeling and tests on the laboratory stand are received.