Application of mathematical statistics methods for predicting occurrence of voltage unbalance in electrical networks

In this paper a statistical analysis of the results of measuring the quality parameters of electric power of the traction substation Uryum 220/35/27.5/10 kV, RU - 35 kV, 1 SS, 35 kV overhead line (VL - 241) located in the Trans-Baikal Territory was performed using the methods of mathematical statistics and probability theory. A particular attention is paid to conducted low-frequency electromagnetic interference by the unbalance factor of the negative sequence voltage (K2U). Voltage unbalance is a fairly common phenomenon in electrical networks of various stress classes and one of the indicators by which the quality of electricity is estimated. Unbalance of stresses significantly affects consumers of electricity, including the supply network itself, and especially negatively it affects the process of operation and the service life of electrical equipment. The relevance of this problem is confirmed by numerous studies on this issue and a significant amount of damage to consumers of electrical energy in service (especially in the Trans-Baikal Territory and the Far Eastern Regions). In the course of the research the form and parameters of the distribution law of a random continuously distributed quantity K2U are determined. To assess the degree of coincidence of the empirical and theoretical distributions, a three-fold test was carried out to verify the validity of the chosen distribution law using the Pearson's χ2, Kolmogorov, and ω2 (Cramer - Mises - Smirnov) criteria. A theoretical logarithmically normal distribution is adopted. The authors determined the likelihood of conducted low-frequency electromagnetic interference on the coefficient of voltage unbalance negative sequence (K2U) for the studied object, besides, the estimation of the service life of the asynchronous motor within certain ranges was made. These ranges are selected basing on the existing interstate standard for the quality of electrical energy GOST 32144-2013. The research results are analyzed. The corresponding conclusions are presented.