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A transient lumped-parameter thermal model of an induction motor is developed. The energy balances and the expressions for the appropriate node couplings representing conduction and convection heat transfer between nodes, as well as the expressions for the heat capacity of each node, are presented. We also present expressions used in a Second Law analysis to calculate the entropy generation and exergy destruction rates at each node. An overall Second Law efficiency for heat transfer through the motor is then defined. The model is validated by comparing calculated temperatures with experimental data for a motor driving an electric submersible pump, showing that the lumped-parameter approximation is sufficient to accurately calculate temperature distributions in the motor and to capture temperature changes during warm-up and cooldown. Finally, the Second Law analysis is used to determine which components in the motor are contributing most to the inefficiency of the heat transfer process, providing a diagnostic tool for identification of areas in the motor where potential heat transfer enhancements would be most beneficial.