Rotor Thermal Model for Real-time Protection in Adjustable Induction Motor Drives

The protection of the adjustable speed induction motor drives is usually implemented using single-mass thermal model. For more precise estimation of the thermal condition of electrical machine it is advisable to use more complex several-mass models. In this study it was investigated that for frequency regulated machines their rotor can be represented as a single thermal mass. That research allows to simplify the thermal model and to recommend three-mass model for implementation to protect the machine from overheat by means of control system. The recommended masses are rotor, stator windings, and stator iron. The experiments were conducted using 5.5 kW squirrel cage induction machine and proved that its rotor has a single time constant purely visible in the temperature transient.