Evaluation of harmonic effects on the power system distribution

Abstract

The paper addresses the impact of harmonic effects on the distribution of energy in a medium voltage network (20kV). The objective of the paper is to highlight the effect of harmonic currents on transformer heating and transformer load capability when the load is nonlinear. The results of the measurements made during the 24h period are analysed in terms of reducing the power of the transformer, increasing the temperature of the transformer oil and the powers circulation. The paper proposes two relations of calculation of the power losses of the transformer in the case of loads not included in the standardized limits of the power factor and the harmonic content. A simple and largely used way of splitting liabilities and costs of the issues relating to power quality, including reactive power, is to claim that voltage is the power supplier’s responsibility, while current is the consumer’s responsibility. Harmonic current is generally a distribution issue and less a transmission one. A large amount of (harmonic) losses shall occur at the nearest load transformer. Result of the analysis of the measured values and the calculations performed de-rating of the apparent power percentage is between 24-32%, increasing the temperature of the transformer oil with 6% and the circulation of powers shown high values of the deforming power between 60-70 kVAD at an average active power of 950kW. Finally, the paper proposed calculation relationships for energy loss assessment due to non-compliance of total harmonic current distortion (THDi) and power factor within the limits imposed by standards.