THE USE OF EFFICIENCY INDICATORS FOR THE DETECTION OF COMBINED MOTOR ASYMMETRY FAULTS AND THEIR EFFECTIVENESS WHEN USED ON INVERTER DRIVEN MOTOR SYSTEMS

The use of Variable Speed Drives (VSD’s) for the control of AC motor systems in industry is well established and continues to expand year-on-year. The increasing use of VSD's can be found not only in renewable energy applications such as wind turbines and tidal generators but also in transport such as motor vehicles and marine propulsion, as well as industry such as on conveyors, material processing and pumping applications. To ensure safe, reliable and efficient operation of these applications, Condition Monitoring CM is essential.

Following a detailed literature review of established research on motor-driven system CM, it has been found that existing research works are more concerned with detection and identification of specific motor faults. There is a lack of research into how certain motor faults contribute to the degradation of the motor driven system efficiency. Whilst the efficiency monitoring of an AC motor system has previously been researched, being able to measure efficiency decreases caused by certain motor faults and on a VSD system operating in different control modes is not an area that has been studied previously. In fact, new European Union EU draft regulations detailing potential future legislation that may become mandatory to define the efficiency of motor driven systems fed by VSD’s has been drafted, but does not detail how these efficiencies may be measured or monitored in the field.

To overcome the gap in research, this research focuses on the use of efficiency monitoring methods on a VSD-driven motor system to measure any reduction in efficiency at an early stage caused by minor motor faults.

The studies are based on model simulation of a basic DOL-operated AC motor followed by experimental work on a laboratory test rig where the model simulation is translated to a VSD operating at a fixed-speed with different loads applied.

This research has found that the efficiency reduction of the motor driven system under different faulty conditions can be detected using certain characteristics of the motor signals. Novel findings have also shown that the efficiency of the motor driven system can be improved by selecting different VSD operating modes. The research also shows that different VSD control techniques can help to improve the regulation of motor speed control when the motor is subjected to minor faults.

These findings are important as they provide proof-of-concept for users of VSD systems who may wish to implement efficiency monitoring strategies on their VSD-operated motors with the minimum of intervention. Furthermore, simply by changing the operating strategy of the users VSD, there may be immediate efficiency benefits offered to the equipment that do not require any new hardware.