Electric motor winding temperature prediction using a simple two-resistance thermal circuit
Purpose - The purpose of this paper is to propose a simplified thermal circuit to estimate the temperature rise in the winding of a totally enclosed fan cooled electric motor for different loads and/or cooling conditions since the motor has already been tested for a known condition. Design/methodology/approach - The determination of the convection resistance is based on classical Nusselt correlations and the value of conduction resistance is provided from a known load condition and the corresponding temperature rise in the winding. Findings - Predicted temperature values showed good agreement with the experimental results, demonstrating that the hypothesis of simplification to a punctual source of thermal energy is acceptable. Research limitations/implications - It is necessary that the motor has already been tested for a known condition (losses, temperature, and ventilation). Although the basic idea of this methodology is based on the use of a reference test condition of the same motor, as a suggestion, with small modifications the same methodology can be used to estimate the thermal behavior of different sized motors, provided a similar motor has already been tested. Practical implications - This approach results in a fast methodology to estimate the thermal behavior of an electric motor in different loads and/or cooling conditions. Originality/value - The differential of this circuit is the use of only two thermal resistances, one for the whole conduction and the other for the convection. This approach is a way to overcome the difficulties related to the determination of the thermal contact resistance and the equivalent conduction resistance between the winding and the different isolation systems inside the slots.
electric motors windings temperature circuits thermal resistance heat transfer