Wavelet Based Diagnosis and Protection of Electric Motors

Abstract

Electric machines are electromagnetic energy conversion devices that convert one form of energy into another form. Electric machines have been playing important roles in the developments of modern industrial technology for over a century. Better understanding of energy conversion principles coupled with evolution of new and improved materials has contributed to the developments of machine designs. The applications of electric machines are increasing rapidly with increased technological advancements. The advances of modern digital computers and recent developments in power electronics and semiconductor devices have made revolutionary contributions on the design and control of electric machines. The direct current (dc), induction, and synchronous machines are the three major electric machines that serve industrial, commercial and household needs. The time-stepping finite element analysis has helped in further developments and design optimization of electric machines. Thus, new electric machines such as brushless dc (BLDC) motor, switched reluctance motor, permanent magnet hysteresis motor, permanent magnet synchronous motor, self-excited induction generator, and doubly fed induction generator are developed and implemented for household and industry applications (Rahman, 1980; Slemon, 1992). The electric machines comes in many sizes and forms, and fulfill their function either independently or as part of a highly complex process in which all elements must function smoothly so that production can be maintained. The function of an individual electric machine is normally seen as separable from the rest of the electromechanical system. Not withstanding their high reliability, electric machines face various stresses including faults during different operating conditions. Hence the condition monitoring, faults diagnostic, and protection become necessary in order to avoid catastrophic failures of electric machines. The use of comprehensive monitoring schemes for the continuous assessment of electrical machines is becoming increasingly important. It is possible to provide adequate warning of imminent/incipient failures using new condition monitoring techniques. It is also possible to schedule future preventive maintenance and repair work in addition to present maintenance needs. This can result in minimum downtime and optimum maintenance schedules. Faults diagnosis allows a machine operator to have the necessary spare parts before the machine is stripped down, which also reduce machine outage times. If faults diagnosis is integrated into the maintenance policy, the usual maintenance at specified 12