Estimation of Starting Characteristics of Three-Phase Induction Motors from No-Load Startup Tests

This work addresses some aspects concerning the practical implementation of a method to estimate the steady-state performance of three-phase induction motors. The method requires only the acquisition of stator voltages and currents data during a no-load startup test taken at the final stage of the production line. The first step of the method implemented consists of estimating the parameters of the single-cage model considering both the rotor resistance and leakage inductance variable with slip. In the second step, the steady-state performance is determined using the equivalent circuit and the estimated parameters, thus allowing the motor manufacturer to check if the motor meets all the requirements stated by national and international norms. The main interest here resides in the starting characteristics such as locked-rotor torque and starting currents. Accordingly, to improve the accuracy of the results, some aspects related to the locked-rotor condition were investigated, namely (a) the influence of variations in the voltage amplitude, in particular the voltage drop during the first cycles, on the magnetizing and leakage inductances, (b) the influence of the mathematical expression chosen to model parameter variations with slip, and (c) the impact of the ratio considered between the stator and rotor leakage inductances. Finally, practical results obtained with estimated parameters are discussed and compared with results obtained with calculated parameters.