One of the important problems of electromechanics is choosing the capacitance required for switching three-phase asynchronous motors (AM) into a single-phase network. In fact, the problem comes down to the choice of a capacitance value, at which an operational magnetic field of the motor will be as close to circular as possible. The solution to this problem by using mathematical models of symmetrical electric machines needs setting a number of simplifying assumptions and does not ensure the reliability of calculation results. In the article, we propose a method and an algorithm for the determination of a capacitance value in the winding of a three-phase asynchronous motor powered by a single-phase network, at which a circular magnetic field is generated. The method is based on the mathematical model of AM, which considers the magnetic saturation and current displacement in the rotor rods, and the projection method for solving the boundary problem for the system of electromagnetic equilibrium equations composed in the three-phase axes. The mathematical model developed can serve as a basis for microprocessor control of the motor starting process.

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