Power Quality in Public Lighting Installations

Power quality in public lighting networks is yet not sufficiently studied today. New conditions and requirements arise as a consequence of rapid application of new technologies like LED lighting, lighting control and monitoring, adaptive lighting systems etc. Optimization of reliable and efficient service of public lighting systems can be only achieved if behaviour of individual elements within the system are well described. For erection, operation and re-construction of public lighting networks it is important to have knowledge on behaviour of the network in different conditions. Because currents primarily depend on the supply voltage, it is essential to analyze electrical parameters not only under standard conditions but also under operational conditions. These comprise e.g. distorted or regulated voltage supply. Non-linearity of electrical parameters of luminaires seems to have significant influence on power quality. In luminaires with conventional ballast, non-linearity is generated by discharge lamp as well as choke. The older type of lamp or choke (in aged existing systems), the worse characteristics. Luminaires with electronic ballasts do not provide this effect and are helpful to maintain “clear” networks. However, in the field of public lighting, unlike in interior lighting with fluorescent lamps for instance, electronic control gears still do not reach any comparative popularity. LED luminaires of diverse quality now intrude the market though technology level, as agreed by experts on many forums, do not compete with available traditional lighting approaches, is known for unsolved problems and needs a series of further developments. From the electrical point-of-view, control gears for LED lamps are similar to electronic ballasts. Supply voltage provided by switch-type source is rectified first. Semiconductor components of rectifier act as non-linear elements. Though these control gears have to be equipped with filter of harmonics, many LED luminaires still lack such circuits. For assessment and investigation of power quality characteristics it is indispensable to understand the behaviour of individual elements and then the behaviour of network as a whole. Distribution network impacts the public lighting network (via transformer) and vice versa. To describe the nature of this two-way influence in details is very complicated, thus certain simplifications in order to speed up calculations are applied. For example, nominal values of harmonic voltages or currents can be used instead of distorted (non-harmonic) characteristics. Or for accurate calculation of steady-state network with discharge lamps measured values can be used instead of complicated description of discharge parameters.