Analysis and Mitigation of Harmonics in Power Distribution Network

Abstract

Harmonic distortions for low voltage distribution network is a research area that has not been extensively explored due to the assumption that the harmonics do not adversely affect low voltage equipment. However, field data collected shows contrarily that current harmonic generated by nonlinear residential customer loads do immensely affect distribution transformers by causing speedy deterioration of the transformers insulation. In the past few decades, there have been considerable changes on residential single phase loads in terms of power demand magnitude and appliance electrical characteristics. The main difference between the current residential single phase loads and earlier versions of a few decades ago is widespread use of electronic appliances with Switch Mode Power Supply (SMPS). These loads are rapidly increasing due to advancement of technology in semi-conductor devices and digital controllers. Such appliances generate current harmonic distortions, which stream back to the low voltage distribution network affecting installed low voltage network equipment. The adverse impact of the generated harmonic distortions are witnessed in premature failure of distribution transformers, erroneous recording of energy meters and over-loading of neutral conductors to mention just a few. This study focuses on analysis and mitigation of current harmonics distortions on distribution network. It involved measurement of current harmonics generated by domestic consumers individual appliance and combined appliances at Point of Common Coupling (PCC) and current harmonics streaming at the secondary side of distribution transformers. Transformers’ oil breakdown voltage was analyzed from sampled transformers to correlate between harmonics and degradation of the oil insulation level. The failed transformers for a period of one year in one of the region was obtained and analyzed. Based on the results of the analysis that show high harmonic pollution on low voltage distribution network, a mitigation measure was devised that involved design and simulation of a single phase active filter using MATLAB–Simulink software. From this work, it was found out that loads with similar electrical characteristics aggravate harmonics and loads with dissimilar electrical characteristics attenuate harmonics. Further, the high current harmonics cause speedy degradation of transformer liquid (oil) insulation and lastly the high current harmonics observed at domestic consumers PCC emanating from current domestic appliances can be mitigated by employing a single phase shunt active filter. The designed and simulated single phase active filter, in MATLAB/Simulink environment, the distorted current waveform was noted to be sinusoidal (undistorted) after introduction of single phase shunt AHF and the current harmonic distortion levels obtained were well within the admissible level recommended by IEEE 519-1992, a power quality standard for power utilities and industries.