*The use of renewable energy sources (RES) in electricity, in particular wind power and solar energy, leads to an increase in the variable component of electricity generation.**The investigations aimed to explore the features of the electricity consumption of different groups of consumers, such as the allocation of predictable and stochastic components.*

*To obtain guaranteed stationary processes, a time series decomposition is performed with the allocation of the averaged component, average monthly values and current fluctuations.*

*An analysis of the behavior of the power system deviations of Ukraine from the average hourly values over the course of the day has shown that for deviations of current values from the trend line of the daily turnover characterized by slow variation, with the presence of some systematic component*

*For settlements where power measurements are performed at intervals of 30 minutes, the series criterion should be in the range 17-32 for the daily data set. Deviation of current values from the daily trend line in case of one substation does not meet this criterion.*

*When considering consecutive 6-hour averaged values after their decomposition for the combined power system, we obtain according to the series of criteria that the stationary conditions for the fluctuations of consumption in the combined power system are fulfilled with a probability of 95%.*

*The stationary criterion is fulfilled for 1 hour fluctuations in the power of the Dnipro power system.*

*For individual settlements or their small group, with the application of a 3-hour averaging, stationary conditions are almost non-existent, only in certain months are at the confines of confidence intervals. The nature of the consumption of a separate settlement is significantly different from the enlarged power system by the level of unevenness, the statistical laws are less noticeable here. For 4-hour averaging interval stationary conditions are already fulfilled in all months of the year.*

*So at some intervals, the energy consumption process can be presented as stationary. Taking into account the above-mentioned factor of stationary will allow forming adequate mathematical models of the power system's operation at different scales of consumer associations.*

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