The assessment of waveform distortion in power systems : validation of methods based on single–point measurements

Abstract

The portion of energy converted by non-linear loads in the modern power system is increasing due to the energy-efficiency and sophistication possible with power electronics. Higher voltage and energy ratings are continuously forthcoming. These devices draw non-linear currents resulting in voltage waveform distortion at the Point of Common Coupling due to non-zero supply impedances between voltage source and the PCC. With the increase in waveform distortion comes the demand for better Quality of Supply management. The verification and quantification of the origin of waveform distortion in a power system is a continuous field of study and forms a critical part of the mitigation design. Methods utilizing single-point measurements, usually taken at the Point of Common Coupling, for the assessment of the harmonic distortion generated by loads are continuously being published. It’s been proven by means of computer simulations and laboratory experiments that in an interconnected network where multiple sources of distortion exist that loads have the ability to exchange harmonic active power between each other. This project investigates the latter statement by conducting practical experiments to conclude that loads have the ability to exchange harmonic active power and that multiple synchronized measurements should be taken to assess the harmonic distortion due to a load. Laboratory experiments are carried utilizing an acknowledged single point measurement method. The results are compared to the direction of harmonic active power obtained from utilizing multiple synchronized measurements. To further the information obtained from the laboratory experiments, practical experiments were conducted utilizing the same methods. The results obtained coincided with the results of previously conducted experiments of which the results were published. From the results obtained it was concluded that in an interconnected network where multiple sources of distortion exist that loads have the ability to exchange harmonic active power between each other. Furthermore it was proven that the single point measurement method investigated presented inconsistent results. Ultimately it was concluded that the reason for the inconsistency was due to the fact that loads have the ability to exchange harmonic active power and that the single point measurement failed to acknowledge this.