Permissible Voltage Asymmetry for Asynchronous Motor Control in Non-Nominal Operating Situations

The article is dedicated to the development of methods for theoretical substantiation of the permissible supply voltage asymmetry coefficient for an asynchronous electric motor operating in the steady-state under non-nominal operating conditions. The core of the technique lies in the fact that the heat loss power of the electric motor operating in the steady-state with the actual: load/utilization level, asymmetry degree, and supply voltage is calculated. The calculation is carried out using an L-shaped equivalent circuit of the electric motor, which is connected separately to the voltage components of the forward and inverse phase sequences with the subsequent imposition of the calculation results produced by the algorithm proposed by the authors and developed based on the program in the MathCAD system for each of the components. Provided that we predetermine the motor torque under-voltage u, the degree of asymmetry of voltage k and angular velocity ω – М(u,k,ω); the moment of resistance as a function of the degree of load z and angular velocity ω – Мс(z,ω); and the steady angle speed ωy(z,k) by numerically solving the equation М(u,k,ω) – Мс(z,ω) = 0. Then, we find the power of heat loss ∆Ру(u,z,k) for this angular velocity.