A Survey of Efficiency Estimation Methods of In-Service Induction Motors with Considerations of Condition Monitoring Requirements

Condition monitoring of electric motors avoids severe economical losses resulting from unexpected motor failures and greatly improves the system reliability and maintainability. Efficiency estimation, which shares many common requirements with condition monitoring in terms of data collections, is expected to be implemented in an integrated product. This brings more considerations into the selection of the efficiency estimation methods. This paper presents the results of a literature survey on efficiency estimation methods of in-service motors, particularly with considerations of the motor condition monitoring requirements. Over twenty of the most commonly used methods are briefly described and classified into nine categories according to their physical properties. Six categories of these methods are more related to in-service testing, and are compared in a table summarizing the required tests and measurements, intrusion level, and average accuracy. Estimation of the rotor speed and the stator resistance, the two stumbling blocks of various efficiency estimation methods, are also carefully studied; and commonly used methods are summarized in this paper. Finally, three efficiency estimation methods are suggested for in-service motor efficiency estimation and condition monitoring applications