Set Point of the Thermal Overload Protection of Large Induction Motors by Simulated Testing

This paper proposes and evaluates an electrical and thermal dynamic model to simulate the effect of voltage unbalance in the parameterization of digital protection of the large induction motors. Based on space vectors, the electrical model has variable parameters with temperature, skin effect and saturation. The thermal capacitances and conductance of the thermal model are identified from the MATLAB Simulink parameter estimation tool. The 1.8 MW motor of the feedwater pump of a power plant is evaluated. The errors concerning the stable state temperatures of the manufacturer’s heating test are 1.1 °C for the stator and 0.56 °C for the frame. The temperature increase of the winding during operating cycles with variable load and different unbalanced voltage were simulated and compared with the thermal image of the relay, demonstrating the importance of these tests in the protection adjustment.