Experimental Estimation of Equivalent Circuit Parameters of a Deep Bar Induction Motor

The method of experimental estimation of equivalent circuit parameters of a deep bar induction motor with respect to the skin effect of rotor current and stator iron loss has been developed. In the method, currents, stator voltages and slip in stationary conditions at various loads, as well as currents and voltages in the initial phase of motor starting at s=1 are measured. According to the measurements using the Fourier transform, the input stator impedances are determined for slip s=1 and for slip at various loads. The assumption that rotor resistances are independent of the skin effect for operation slip values allows finding the equivalent current penetration depth into the rotor bar and the parameters of current skin effect coefficients for rotor resistance and reactance by solving the nonlinear equation system. An example of equivalent circuit parameter estimation using the proposed method for an AB series induction motor rated at 630 kW and a stator voltage of 6 kV is given. The close coincidence between experimental and calculated static and dynamic characteristics is obtained. The advantage of the method is its relative implementation simplicity in industrial conditions, which is especially important for high power motors, for which expensive test benches are not always available. The parameters of equivalent circuit have been estimated using the proposed method can be used to study heating of windings in operating and starting conditions, to calculate short-circuit currents at various voltage and frequency levels, to determine the stability of multi-machine load nodes of a power supply system of various industrial enterprises, to determine the settings of relay protection and automation devices.