Condition monitoring of induction motors is a fast emerging technology for online detection of incipient faults. It avoids unexpected failure of a critical system. Approximately 30-40% of faults of induction motors are stator faults. This work presents a comprehensive review of various stator faults, their causes, detection parameters/techniques, and latest trends in the condition monitoring technology. It is aimed at providing a broad perspective on the status of stator fault monitoring to researchers and application engineers using induction motors. A list of 183 research publications on the subject is appended for quick reference.

A review of stator fault monitoring techniques of induction motors

Condition monitoring of rotating electrical machinery has received intense research interest for more than 30 years. However, electrical machinery has been considered reliable and the application of fast-acting digital electrical protection has rather reduced the attention operators pay to the equipment. The area based upon current literature and the author's experience is reviewed. There are three restrictions: only on-line techniques for rotating machines are dealt with; specific problems of variable speed drives are not dealt with, except in passing; conventional rather than emerging brushless, reluctance and permanent magnet machines of unusual topology are concentrated upon. The art of condition monitoring is minimalist, to take minimum measurements from a machine necessary to extract a diagnosis, so that a condition can be rapidly inferred, giving a clear indication of incipient failure modes. The current state of the art is reviewed in the following ways: survey developments in condition monitoring of machines, mechanically and electrically, over the last 30 years; put that work in context alongside the known failure mechanisms; review those developments which have proved successful and identify areas of research which require attention in the future to advance the subject.

Review of condition monitoring of rotating electrical machines

The fault diagnosis of rotating electrical machines has received an intense amount of research interest during the last 30 years. Reducing maintenance costs and preventing unscheduled downtimes, which result in losses of production and financial incomes, are the priorities of electrical drives manufacturers and operators. In fact, both correct diagnosis and early detection of incipient faults lead to fast unscheduled maintenance and short downtime for the process under consideration. They also prevent the harmful and sometimes devastating consequences of faults and failures. This topic has become far more attractive and critical as the population of electric machines has greatly increased in recent years. The total number of operating electrical machines in the world was around 16.1 billion in 2011, with a growth rate of about 50% in the last five years [1].

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Trends in Fault Diagnosis for Electrical Machines: A Review of Diagnostic Techniques

Signal based condition monitoring techniques for fault detection and diagnosis of induction motors: A state-of-the-art review

Electrical insulation plays a critical role in the operation of motor and generator rotor and stator windings. Premature failure of the insulation can cost millions of dollars per day. With advancements in electronics, sensors, computers and software, tremendous progress has been made in the past 25 yr which has transformed on-line insulation monitoring from a rarely used and expensive tool, to the point where 50% of large utility generators in North America are now equipped for such monitoring. This review paper outlines the motivation for online monitoring, discusses the transition to today's technology, and describes the variety of methods now in use for rotor winding and stator winding monitoring.

Advancements during the past quarter century in on-line monitoring of motor and generator winding insulation

Partial discharges are a symptom of most of the stator winding insulation deterioration mechanisms found in motors and generators rated 6 kV or more. Thus, partial discharge testing has been used for over 40 years as a means of determining the maintenance requirements of such high voltage stators. As the benefits of such testing have become more widely known, there has been an interest to apply partial discharge testing to 4 kV motor and generator windings. This paper discusses the theoretical reasons which may limit the testing of 4 kV stators. The results of an extensive series of offline partial discharge tests are presented which indicate that partial discharges indeed do occur. The results of a series of online partial discharge tests conducted on about ten 4 kV motors over the past two years show that partial discharges may only occur for a short time prior to failure with some types of failure mechanisms. Thus to prevent in-service failures, continuous monitoring is necessary. An inexpensive continuous partial discharge monitor is described. It seems that partial discharge monitoring will only be cost-effective for very critical process motors and generators where in-service failures may have large financial consequences.

H.G. Sedding

Papers

Monitoring partial discharges on 4 kV motor windings