Ensuring of rational voltage mode by means of automatic change of power transformer under load (OLTC) transformation coefficient under conditions of load parameters variation and configuration of supplying lines is considered. The technique of a choice of a determining voltage mode of connection in power supply system of enterprises on extraction, transportation and processing of mineral resources with application of methods of the theory of fuzzy sets is offered. Parameters are used, which allow describing the state of distribution lines and electric consumers, dispersion of load along them, damage at a voltage deviation from a rational level in real time. The structure of control system based on fuzzy logic is given. The graphs of the membership functions of five parameters, the totality of which determines the power supply line mode, are given.
