MOTOR TEMPERATURE ESTIMATION INCORPORATING DYNAMIC ROTOR IMPEDANCE

This study investigated the estimation of induction motor temperature at different system, motor and load conditions. Previous studies assume a linear relationship between rotor impedance and frequency when estimating motor temperature. Other attempts assume the heat loss in the motor is adiabatic. In this study motor temperature is estimated using comprehensive interactive electrical, thermal and mechanical models. The electrical model accounts for the skin effect in the rotor bars and predicts the dynamic motor impedance as motor speed changes. The thermal model accounts for the heating and cooling process in the motor. The interactive model is used to study motor behavior during balanced system condition, unbalanced system condition, high inertia load, locked rotor and overload situations. Motor temperature during these states is predicted. It is shown that under certain conditions motor starting time may exceed the locked rotor time. Rotor thermal limit curves during unbalanced voltage condition are presented.