New results of investigating the characteristics of voltage quality in distribution systems and problems of their evaluation

The paper presents the results of a campaign of measurements of voltage dips and short interruptions in LV networks. The impact of the choice of threshold voltages and of several conditions are analysed and the table of annual numbers of voltage interruptions, dips and swells which will not be exceeded with the probability of 95% is presented. Further attention is focused on flicker, harmonics and THD in EHV networks. The authors conclude that the IEC limits taken over into the Czech Transmission and Distribution Codes are too strict. The paper also presents the results of the measurement of power quality characteristics in LV, MV and 110 kV distribution networks and the trends of changes of selected parameters during the interval of 3 and 6 years.