Оцінка імовірнісної несиметрії струмів і напруг на основі графіків навантаження комунально-побутових споживачів

Мірошник О. О.

Анотація


The estimation of probability unbalanced currents and voltages based on the graph of household consumers load

O. O. Miroshnyk

 

The theoretical study and recommendations on the practical application of methods for calculating the probability of asymmetry in the four-wire networks of  0.38 / 0.22 kV were carried out through using the load curves on the duration at the substation. Research studies focusing on analysis of the operation modes of distribution networks with voltage up to 0.38 / 0.22 kW, indicated that due to current unbalance the work of municipal household load, of which the majority are single-phase power-receivers, which are unevenly distributed over the phases and have a casual character inclusion. It is shown that there are two types of asymmetry: the systematic and probabilistic (or random). Systematic asymmetry caused by uneven load phase constant over time, probabilistic asymmetry corresponds to loads that vary over time by chance (intermittent asymmetry). When considering the asymmetry of probability random variables are currents in the phases of the three-phase circuit. Since the voltage drop are linear functions of phase currents, and that the distribution law is the same as for the currents.

It is shown that in practice, the load distribution probabilities curves (graphs of probability densities) are unknown. However, the load graphs expressed with powers or currents may be known. Currents are much more common when operating substations. There is a simple correlation between the probability density pressures graphs and loads graphs, which are rearranged in length. If the load curve equation in duration is known, the equation of the probability density graph of the load and vice versa can be obtained easily. The method of solving a probabilistic assessment of the problem of asymmetry in the three-phase four-wire network was considered. To solve this problem it is necessary to know the equations of load graph on duration and the function that defines the range of integration. On unmanned substations the load graphs can be obtained by special measurements, and on manned substations they are built regularly on the indications of special devices.

We solved the task of evaluating the probabilistic assessment of asymmetry at the currents corner symmetry and single-phase equal the average power factor values. The graphs show dependencies of currents symmetrical components in four-wire networks of  0.38 / 0.22 kV, which showed that the error under graphs approximation of household consumers does not exceed 5%.

We cited a group of curves, which show the variation of coefficient of filling the graphs from the share of power consumers in the total load for the consumer substations with different installed capacity. The dependence of the exponents approximating function for all kinds of load profiles of consumer transformer substations of 10 / 0.4 kV are defined. The verification of the integral probability completed. It based on the statistical processing of the results of numerous direct measurements of the phase currents on the transformer bushings consumer substations of 10 / 0.4 kV. A statistical analysis of measurement data in the rural distribution network 0.38 / 0.22 kV completed. It showed that the distribution of the currents in the phases obeys the normal law.


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