Abstract: The increase in unbalanced and non-sinusoidal loads is one of the main factors of power quality deterioration. In this regard, new methods of rational use of power resources are required. This study is devoted to the impact study of non-sinusoidal load parameters on real-power losses in three-phase two-wound power transformers by means of constant coefficients. This study provides an algorithm to calculate transformer total power losses using a developed method of constant coefficients. This method allows going back from the classical method of equivalent circuits for each harmonic component. We have used the electrical circuit theory, modern methods of electric circuit analysis and synthesis, the equivalent resistance method and the method of equivalent sine to achieve this purpose. Branch currents are calculated in one phase of equivalent circuit of TWTL system based on this equivalent circuit (magnetic coupling of HV and LV windings, replaced by their electrical equivalent and parameters of LV windings are under HV). In connecting capacity load to LV terminals, signs “plus” of the last real and imaginary numerator terms and of the last denominator term should be changed to negative in the right-hand side of the last equation. Thus, we have determined the total power losses in single-phase transformer under non-sinusoidal load (in one phase of a 3-phase transformer) by summing up the power losses of each harmonic component in the load. The proposed calculation algorithm for transformer real-power losses by developed method of constant coefficients allows going back from the classical method of equivalent circuits for each harmonic component.