Validation of popular nonsinusoidal power theories for the analysis and management of modern power systems

Abstract

Non-sinusoidal conditions are characteristic of modem electrical power systems. Technological advances such as that of the rapidly developing solid-state technology has accelerated the nonlinear loading of power systems. The thesis firstly reformulates and demonstrates multi-frequency power system analysis techniques. Of special importance is the definition of energy under non-sinusoidal conditions. Popular non-sinusoidal power theories are evaluated and the approach of Czarnecki is shown to have an important deficiency in practical power system applications. The Czarnecki three-phase power components are shown to be questionable as to their physical significance. It is proposed that energy formulation should be carried out in a transformed domain and it is demonstrated that the well-known Park current and voltage vectors enable valid descriptions for energy phenomena in three wire three-phase power systems. A new transform that transforms four wire three-phase quantities to three-dimensional space vectors of voltage and current is shown to deserve further investigation towards implementation in compensation techniques and tariff systems. Knowledge on the relative contribution to the overall distortion of a specific source of distortion in a power system requires the localisation thereof and a measurement technique. It is shown through time-domain modelling that it is not possible to localise distortion sources through single-point measurements in power systems in the presence of multiple harmonic distortion sources. This principle renders all attempts to quantify power system distortion through single-point measurements invalid. The implication is that penalisation of distorting customers by measuring their emission, will not be possible if all nodes over the power system is not measured synchronously. Therefore, final proof to this principle is given through the results obtained by measurements taken in a real-life power system. The novel combination of a new power quality index and a distributed measurement system that does not require accurate synchronisation in time is proposed as a practical approach in quantifying distortion contribution of specific distortion sources and should be investigated further. It can aid towards managing non-sinusoidal conditions in a power system through the implementation thereof in a self-regulating tariff structure.