A comparative study into the application of the NRS 048, IEEE 519-1992 and IEC 61000-3-2 on harmonic apportioning in a discrimitive tariff

Abstract

Development in power electronics enabled sophisticated energy conversion. These new solid-state energy conversion processes are energy-effective, but are inherently non-linear which means that the load current is typically non-sinusoidal in shape although fed by a sinusoidal voltage source. Although the utility strives to guarantee a pure sinusoidally shaped voltage waveform at every Point of Common Coupling (PCC), harmonic currents deteriorate the overall power quality in the power system. Various undesirable effects of nonsinusoidal conditions in a power system are, possible resonance at power factor capacitors, metering errors, increased reactive power, increased motor losses, increased transformer losses, increased line losses and additional heat in cables and equipment. Harmonic distortion on the power system and within customer facilities is a growing concern due to the growth in non-linear loads, which manifests as higher distortion levels throughout the entire power network. This phenomenon has reached a magnitude where several international bodies have proposed harmonic apportioning standards (IEEE 519-1992 (America), IEC 61000-3-2(Europe) and NRS 048 (South Africa)). These standards provide the Electricity industry with guidelines in apportioning a predetermined level of harmonic emission per customer connected at the PCC. The harmonic apportioning standards had the result that users and suppliers must be partners in an effort to maintain the quality of supply whilst the network expands. The impact that harmonics can have on the network and other equipment operating from it can range from a minor annoyance to a system malfunction and disruption in operation. Harmonics directly influence the effectiveness of the operation of the utility and its revenue. Customers will not only experience continuous energy losses, but also major production losses when the supply to a plant is disrupted. The harmonic load currents force the utility to have a higher real energy input then the actual real power needed to maintain a plant's production at a certain level. The utility carries the extra transmission losses due to the extra l2R losses caused by the harmonic currents. Installed power system capacity will be higher then necessary for pure linear loads. Traditional energy rates fails to accounts for these effects. A fair tariff structure thus have to be design, which may allocate the cost of waveform distortion according to the relative contribution of loads connected to the PCC, and which will require the utility to supply a minimum distorted voltage signal at the PCC. Such a tariff structure should also recognize the installation of equipment by customers which decrease the Total Harmonic Distortion (THD) observed at the PCC, or when they implement new technology, which withdraw sinusoidal load currents.