Electric motor winding temperature prediction using a simple two-resistance thermal circuit

This paper proposes a simplified thermal circuit to estimate the temperature rise in the winding of a totally enclosed fan cooled (TEFC) electric motor for different loads and/or cooling conditions since the motor has already been tested for a known condition. The differential of this circuit is the use of only two thermal resistances, one for the whole conduction and the other for the convection. 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. This approach results in a fast methodology to estimate the thermal behavior of an electric motor in different situations. This significantly reduces the time necessary to determine geometric and theoretical/experimental parameters, such as contact resistances.