Superposition methods for on-line determination of a.c. machine winding resistance

The resistance method is a well-known procedure to determine winding temperatures of electrical machines. In normal use a machine is tested off-line, after reaching thermal equilibrium running at specified condition, immediately after shutting down at standstill. Further interest is devoted to on-line methods allowing the determination of temperatures during a.c. machine operation. This opens possibilities to monitor temperatures under different service types. The paper discusses known superposition methods to inject a d.c. current component using passive elements, and new methods making use of semiconductor devices. Considered are procedures to inject d.c for machines running on inverter supply. Several tests were made on a laboratory induction machine setup. The procedures are described, and results are discussed