Lumped parameter thermal model for electrical machines of TEFC design

TLDR

A lump‑parameter thermal model for TEFC electrical machines provides steady‑state and transient temperature predictions at most locations, including peak end‑winding and rotor surface temperatures. The model is derived from dimensional data and constant thermal coefficients, enabling adaptation to various frame sizes, and its application to a 75‑kW and two 5.5‑kW induction motors is detailed. The model, solved via eight linear differential equations, accurately predicts TEFC machine temperatures, enabling online estimation for protection and duty‑cycle evaluation, and its performance is validated by experimental data from load tests on three induction motors.

Abstract

A lumped-parameter thermal model is described which provides both a steady-state and transient solution to the temperatures within an electrical machine of the TEFC design. The model is sufficiently complex to identify the temperatures at most locations in the machine, including the peak temperatures in the endwinding and the surface temperatures of the rotor. It is formulated out of purely dimensional information and constant thermal coefficients and is therefore easily adapted to a range of frame sizes. The thermal behaviour of the TEFC machine is accurately described by the solution of just eight linear differential equations. The model is therefore suitable for application to online temperature estimation for protection and duty-cycle evaluation. The application of the thermal model to a medium (75 kW) and two small (5.5 kW) induction motors is described in detail. The model performance is confirmed by experimental temperature data obtained from varying load tests on each of the three induction motors.