In design. According to its results the design scheme can be approved or modified to ensure the building of a reliable motor.
This paper presents a mathematical model that calculates the thermal behaviour of wedge-type rotors under different operating conditions. The model is based on the concept of building an equivalent thermal network of the bar. The number of lumped thermal meshes, and in turn the number of required differential equations, depends on the number of fictitious sub-sections into which the bar cross-sectional area is divided. The model considers skin effect during the starting period as well as the temperature effect on the current density distribution and the bar resistance. Further more, the proposed model has the ability of applying the topological network analysis.
Therefore, and regardless of the number of subsections. the process of building the required equation system can be carried out by a relevant computer routine.
The written computer programme, simulating the mathematical model can be integrated with any design routine of high-starting torque squirrel cage induction motors. It calculates the temperature behaviour at a group of successive locations on the bar-depth in addition to the temperature distribution along the bar-depth at different instants during starting towards steady-state. Effect of wedge attained maximum and operating temperatures had been studied the especially after frequent restarts under rated or different lead -ratios.
The analysis of the computed results forms a knowledge-base which supports the choice decision about the wedge-shape, operational limits and thermal information required for protection systems.