• Energy Research

t. The aim of this work is to justify a criterion selection for the frequency estimation of the 6- 10 kV-overhead lines’ technical condition (OL), using the reliability indicators of the overhead lines (failure intensity, mean time between failures, reconditioning intensity and recovery mean time). To achieve the goal a retrospective method was used for obtaining information on reliability and a statistical method for analyzing the reliability of the multiple-action products to justify the frequency criterion. Certain methods of mathematical statistics were applied to process the information obtained. In particular, the Kolmogorov criterion was used to support the hypothesis on the exponential law of distribution of the OL failures and the time of their recovery. Based on the analysis of the 6-year overhead line failures database, the exponential law hypothesis of distribution of the overhead line failures and the time of their recovery was accepted and confirmed. The most essential result is the experimental and theoretical confirmation that the complex indicator of reliability, i.e., the technical preparedness coefficient with account of self-eliminating failures, can be used as the frequency criterion for verification of the OL technical condition. High precision of the criterion has been proved even at a small number of failures. Significance of the results obtained consists in that, while controlling the dynamics of the coefficient and comparing it with the normative values with respect to the OL reliability category, it is possible in due time to fix a date for the OL technical condition checking.

The purpose of this work is the theoretical substantiation and development of a practical method for calculating the exchange fund of electrical equipment of an industrial enterprise. The purpose is achieved through the use of separate methods of queuing theory if the flow of applications for repairs and restoration are the simplest. It is confirmed by the results of statistical studies. Therefore, for the mathematical description of the repair problem the authors use the scheme [Mm; Ms; n], which corresponds to the process of death and reproduction. As a criterion for optimizing the exchange fund of electrical equipment it is proposed to use the zero probability waiting for the replacement of a faulty electrical component with a working from the exchange fund. For the case of the simplest flow of applications for service, the authors suggest to use the Peck and Hazelwood tables, which significantly simplify the calculation of the exchange fund for known failure rates and electrical equipment recoveries. For practical use of the proposed method, the authors have developed convenient forms for presenting initial data for calculating the exchange fund, and it is proposed to present the results of calculations in the form of several options for the optimal number of electrical equipment in the exchange fund depending on the accepted level of zero expectation probability, the number of elements from the exchange fund and their recovery time. The proposed method will optimize the exchange fund of electrical equipment and reduce the cost of its formation.

The paper describes the results of the study of an optimum interval for switching the stages of the capacitor unit (CU), which can improve the efficiency of automatic control of reactive power, reduce the wear and tear of the switching equipment and capacitors and prolong their service life period. The urgency of the research is determined by the lack of well-founded recommendations on the selection of the optimum switching interval for the CU stages. The recommendations on the selection of the optimum switching interval for CU stages are developed on the basis of the numerical simulation method using real reactive power curves of consumers and the Lab+ software program modelling the reactive power regulator. The optimum interval for switching capacitor banks, indicated in the settings of the automatic reactive power controller, is determined in relation to the reactive load conditions. For medium and abruptly variable reactive loads, it is very important to accurately monitor the load changes and control the reactive power generation at the maximum frequency, i.e., to use a minimum switching interval for the CU stages, which is to be no less than 120 seconds. For weakly variable loads, setting a minimum control interval does not lead to a significant reduction in the reactive power flow, and even increases the power flow in some cases. Therefore, prolonged switching intervals of 8, 15, 30 minutes are the most efficient and cost-effective for loads that do not significantly vary over time. The results obtained can help to improve the efficiency of automatic control of CU reactive power.

The aim of this work is to substantiate the idle time evaluation of the overhead power line (OPL) according to the reliability indicators of its main elements using the probability value of the overhead power line availability factor. Statistical studies of the 17 OPL were performed to achieve this goal. The results of the statistical data processing made it possible to consider over-head lines as objects of a multiple action, and their failure and recovery flows as the primitive Poissonian flows. The calculation of the Wilcoxon and Pearson criteria confirmed the uniformi-ty of the statistical material both in terms of failure times and recovery time for all 17 studied OPL, which allowed combining the uniform statistical data into two representative samples, ac-cording to failures and recoveries, for the generalized district OPL and calculate its reliability indicators. The most significant result is the justification of applying queuing theory methods to evaluate the idle time of 6–10 kV single-chain and double-chain of overhead lines. The signifi-cance of the results obtained consists in that a simple engineering method is proposed to evalu-ate the availability factor of the overhead power line according to the reliability indicators of its main elements, which allows predicting the idle time of the overhead line for the upcoming cal-endar year of its operation. The newly obtained availability factors of the main overhead line elements can be used in the overhead power lines’ design.