The article describes the sequence of formation of the growth coefficient of the transformers power scale, taking into account the operational indicators of substations. For this purpose, an expression for finding the optimal power of 110 kV transformers has been developed on the basis of a technical-economic model of costs for the transformation of electrical energy. The developed expression is used to find the optimal power of transformers of 110 kV in conventional units, taking into account the load of substations, which is the basis for the formation of the growth coefficient of the transformers power. The search for optimal power was performed on the basis of deviations of the indicators of the maximum load of transformers and the time of maximum losses. The time indicators of maximum losses and maximum load are calculated according to the hourly load data of transformers, taking into account the presence of generation nodes on the secondary voltage buses. The formation of the growth coefficient of the scale of transformers is performed by finding the mathematical expectation of the optimal power and its shift based on the boundaries of the distribution of two adjacent powers of transformers. The substantiation of the formed coefficient of growth of the transformers power was performed according to the criterion of minimum technological losses of electrical energy, by comparing the daily loses schedules in transformers. According to the research results, it follows that the application of the obtained coefficient allows to reduce the level of technological losses. The study was carried out on the example of operating substations with two-winding transformers of 110 kV using the scheme of the established mode of operation of the electric network.