Power quality monitoring in regional distribution networks in the Czech Republic
XI Forum Energetyków GRE 2008/Międzynarodowa Konferencja Naukowo-Techniczna(19-21.05.2008;Orle Gniazdo Szczyrk,Polska)
The liberalisation of the market with electrical energy came into effect in the Czech Republic on 1st January 2002. In the first phase, big consumers (consumption over 40 MWh per year) were affected. This market has been liberalized completely since 2006. In our opinion, power companies pay sufficient attention to ensuring the required technical parameters. Customers usually have only one technical choice of the supply of electrical energy. But in the liberalised market environment entitled customers can choose from several traders of electrical energy. The key criterion for the choice is surely the offered price. But in steady market environment, where the offered prices will be balanced, other parameters will be more important when making decisions, and we expect that ensuring quality parameters will increase its role. The quality of electrical energy can be looked upon from the point of view of technical parameters of the supplied voltage and current, or from the commercial point of view (the quality of the supplied electrical energy and services). In the power company CEZ in the North Moravia region the monitoring of a number of selected parameters of the quality of electrical energy (harmonics, flicker, unbalance) is being done in cooperation with research laboratories of the Faculty of Electrical Engineering and Computer Science, VŠB - Technical University of Ostrava. The monitoring is being done in a complex way in 59 feeding points 400 V, always in one week intervals, and at the same time on all voltage levels (HV, MV and LV). The whole cycle lasted for 3 years, and currently the fourth cycle of monitoring is realised. 3 full cycles enables comparing of the state after twice three years. In the paper, the results of the first, second and third cycle of the complex monitoring will be summarised together with the comparison of the changes of parameters after three years. In the second cycle of monitoring there were measured currents in the neutral conductor. The results of monitoring of harmonic components of current in the neutral conductor will be presented in the paper. Beyond period monitoring are installed on chosen 100kV substations stationary monitoring devices. Analyzers QWave Power and QW Light (by the LEM Company) are installed here, so it is possible to record as many informations about both individual voltage quality parameters and events in the distribution system as possible. QWave Power measures all parameters of voltage quality simultaneously and compares these with limit values of the standard CSN EN50160, and further analyses the current. QWave Light is a simplified version that evaluates only voltage in all its guaranteed and indicative parameters. The instruments are successively installed in other MV and HV nodes. This paper summarizes results of 10 years of long-term periodical power quality monitoring. Further are in detail described methods of power quality monitoring methods with focus on use of composite measuring instruments.