PRZEGLĄD ELEKTROTECHNICZNY (Electrical Review), ISSN 0033-2097, R. 88 NR 9a/2012 103 violate the required value of power factor high harmonic distortion as a result of the use of unprotected compensation poor reaction speed of compensation reduced capacitor life as a result of high ambient temperature voltage dips and interruptions high harmonic distortion as a result of used appliances overloading of the transformer as a result of the high share of reactive power reaction breakers caused by harmonics flicker others 0 5 15 25 35 frequency (%) Alena OTCENASOVA, Juraj ALTUS, Petr HECKO, Marek ROCH Slovakia, University of Zilina, Faculty of Electrical Engineering, Department of Power Electrical Systems Measurement characteristics of voltage in practice and possibilities for improvement of voltage Abstract. Worsened quality of supplied as well as demanded electricity causes in reality a large financial loss. The main quality parameters monitored today are voltage dips and interruptions. In this context there are relevant statistics of measurement results and especially the possibility of their improvement by using Dynamic Voltage Restorer, for which we have proposed a possible method of control. The proposed regulation DVR is based on Park transformation of immediate values of voltage in network and its feedback transformation. The method is shown and verified on simulation model. Streszczenie. Pogorszenie jakości dostarczanej jak również zapotrzebowanej energii elektrycznej powoduje powstawanie dużych strat finansowych. Podstawowymi parametrami jakościowymi monitorowanymi obecnie są spadki napięcia i przerwy w zasilaniu. W tym kontekście istnieją adekwatne statystyki pomiarowe, a w szczególności możliwości ich poprawy poprzez użycie dynamicznego układu odtwarzania napięcia (DVR), dla którego zaproponowaliśmy metodę sterowania. Proponowana metoda sterowania układem DVR bazuje na transformacji Parka wartości chwilowych napięcia w sieci i ich transformacji odwrotnej. Metoda została przedstawiona i zweryfikowana na modelu symulacyjnym. (Pomiary parametrów napięcia w praktyce i możliwości poprawy jakości napięcia) Keywords: power quality, electrical network, voltage dips and interruptions, dynamic voltage restorer, controlling of DVR. Słowa kluczowe: jakość energii, sieć elektryczna, spadki napięcia i przerwy w zasilaniu, dynamiczny układ odtwarzania napięcia, sterowanie układem DVR. Introduction Problems with power quality are always hot topic. The quality of electricity is influenced by many factors and to keep the parameters within the required limits is in many cases difficult. Worsened quality of electricity is often caused by customers by the nature of theirs operation. As they are in many cases supplied together with other customers from the point of common coupling it can lead to a situation where one customer’s device may retroactively influence also other customers. Likewise, negative influences can come from a distribution and from the transmission system too. Study [1] focused on the problems with power quality prepared by the David Chapman from the Copper Development Association confirms that supplied electricity, whose quality does not satisfy relevant standards, causes huge economic losses. During resolving study David Chapman calculated concrete values of losses and says that the problems with power quality cost industry and business in the European Union around 10 billion euro per year. Quality parameters of voltage In general, power quality is evaluated according to the quality of electrical voltage. Basic characteristics of the quality parameters are given in the STN EN 50160 „Voltage characteristics of electricity supplied from the public distribution networks” [2]. This standard applies to low and medium voltage supply and is generally valid. It is applicable to electricity networks in European industrial areas, as well as the electricity network supplying the „two families isolated in the desert”. This leads to various quality requirements. For many customers is the quality of voltage low even if it satisfies the requirements for quality according to STN EN 50160 and electricity is unusable (for example, the frequency of interruptions and voltage drops). Therefore stricter standards exist, for example STN EN 61000-2-2 and STN EN 61000-2-4 [3]. It is important that the customer has agreed properties of energy supplied according to the standards that match the type of operation with suppliers of electricity. Standards that characterize quality parameters of electricity and specify the limits of parameters serve to ensure the functionality of devices supplied from this network, as well as devices that are connected to the network later [4]. Problems with quality of electricity in operating practice Power Grid Company [5] deals mainly with power quality measurement, delivery devices that increase the quality of electricity supply and distribution activities of components that are necessary for the production of compensation units, of low power electronics and semiconductors. Fig. 1 shows the statistical processing of various problems in industrial networks. These data are measurement results done by Power Grid Company [5] mainly in Slovakia and minor share in the Czech Republic. Fig.1. Statistics of the most frequent problems measured by the Power Grid Company From the qualitative parameters listed in Fig. 1 dips and interruptions of supply voltage cause the highest economic losses [6]. Voltage dips and interruptions are especially dangerous for a group of customers, which are called the sensitive customers. For these customers even short time voltage dip may have the same economic impact as a long- term interruption of power supply. Examples of industries that are the most sensitive to the quality of power supply, including the costs to be paid on one fault (in dollars), are shown in Fig. 2 [6].