Restriction factor for quantitative analysis of the turns ratio changing of the power transformer

According to service rules the number of coil's windings of power transformer is adjusted to obtain the normal voltage value on consumer side. Usually it is required in winter time, when load power is growing. The turns ratio declining leads to the rise of the voltages on the transformer second winding and on the consumer's distribution bus. The paper main goal is to show that sometimes it is desirable to refuse this option because of some negative consequences. First, the load reactive power's rise squared as voltage due to magnetizing currents. So for load with poor power factor and huge power dispersion the turn ratio changing wouldn't an aid. Second, the turn ratio reduction causes the THD increase of currents and voltages. It might be vital when harmonic source is on consumer side. To quantify possibility and utility of the turn ratio changing the restriction factor is introduced. The restriction factor considers a load profile, power grid parameters and presence of harmonic sources. Mathematical model of the power grid with two voltage levels and an inconstant load is presented in the article. The data of simulation with load profiles that are typical for enterprises is presented and described.