Effect Of Harmonic Loads On Over Current Relay To Distribution System Protection

Abstract

Abstract. The effects of non sinusoidal voltages and currents on the performance of electromechanical characteristic inverse of over current relay protection were experimentally studied. The test were conducted such that the Total Harmonic Distortion (THD) current, frequency, amplitude and phase shift of individual harmonics could be controlled by employing a waveform load harmonic. The relation between the harmonics currents and voltages were modeled through the power system impedances within residential distribution systems. It was found that for harmonic voltages and current amplitude, as they occur in distribution system, time delay operation of over current relays showed longer. The experiment results, it was clear that when THD increased making the operation time of over current relay longer, and on distribution system showed that with Irms 122 A and THDi 0%. When THDi increased to 37.2 % the fundamental current had 115 Ampere and operating time relay delayed. Keywords, Distortion Harmonic, over current relays, Distribution system