Joseph Sottile

Alternatives for assessing the electrical integrity of induction motors

The authors present alternative appropriate for detecting incipient failures in three-phase induction motors of the sizes commonly found in the process industries, with an emphasis on techniques resulting from a recently completed project. The techniques discussed are divided into three categories: periodic tests, sequence tests, and the decision-function method. The use of the effective negative-sequence impedance test is recommended for in-plant predictive maintenance applications. This test is sensitive to a wide range of degradation mechanisms that will ultimately result in motor failure, and its use can allow for timely repair of the motor before costly downtime or a catastrophic failure is incurred. The technique can be applied while the motor is in operation. It is recommended that this predictor be monitored continuously, rather than being applied on a periodic basis, because an appropriate interval between tests cannot yet be defined. The use of the decision-function method will allow a more detailed analysis of motor performance and condition. However, the price for achieving this increased information is high and may not be warranted in many situations.<<ETX>>

An on-line method to detect incipient failure of turn insulation in random-wound motors

Induction motors used in various mining industry applications fail frequently because they are subjected to severe operating conditions. Periodic test procedures are inappropriate for many installations and the cramped and hazardous mining environment makes unscheduled motor replacements difficult and time-consuming to perform. An online detector of insulation degradation is proposed and demonstrated analytically and experimentally. This detector, termed the effective negative-sequence impedance, is computed from the voltage and current phasors at the motor terminals. It can be used frequently, even continuously, and does not interfere with normal motor operation. With this detector, motor replacements can be scheduled, thereby reducing production downtime associated with emergency maintenance actions. >

Condition monitoring of stator windings in induction motors. I. Experimental investigation of the effective negative-sequence impedance detector

The former US Bureau of Mines funded a research project aimed at developing the enabling technology for incipient failure prediction in electric power system components as a means of reducing the injuries and fatalities that sometimes occur when equipment malfunctions. Over the ensuing years, interest in this has waxed and waned, but interest has been growing for both civilian and military applications. This paper addresses the level of turn-to-turn insulation deterioration that can be resolved using an online monitoring technique based upon an effective negative-sequence impedance detector. The detection of turn-to-turn defects is especially important because they are believed to represent the beginning stage of most motor winding failures.

On-line condition monitoring of induction motors

Condition monitoring of induction motors is a process that may be used to great advantage in mining and other industrial applications. The early detection of motor winding deterioration prior to a complete failure provides an opportunity for maintenance to be performed on a scheduled routine without the loss of production time. Presented in this paper is a theoretical and experimental analysis of a voltage mismatch technique that may be used in operating situations to monitor the health of induction motor windings. It extends previous work in this area by demonstrating the robust nature of the monitoring process not only under conditions of power supply unbalance but also in situations where motor construction imperfections exist and mechanical loads are unpredictable. A suggested procedure for application of this condition monitoring process in industrial situations is also included.

Condition Monitoring of Brushless Three-Phase Synchronous Generators With Stator Winding or Rotor Circuit Deterioration

This paper presents experimental and theoretical analyses used to establish electrical features that can be utilized as indicators of armature winding, field winding or rectifier diode deterioration in brushless three-phase synchronous generators before the imperfection progresses to become a ground fault. The paper begins with the description of a 5 kVA synchronous generator specifically designed and constructed to allow for simulation of armature winding, field winding or rectifier diode deterioration in a brushless machine. Subsequently, a description of the experimental methodology and the results of experiments are presented. Specific features that can be used as indicators of the deterioration are described and a theoretical basis for them is provided. The proposed features can be obtained continuously during normal generator operation. As such, they can be used as a basis for both winding brushless and brush-fed synchronous generator health monitoring applications.

Condition monitoring of stator windings in induction motors. II. Experimental investigation of voltage mismatch detectors

For pt.I see ibid., vol.38, no.5, p.1447-53 (2002). Condition-based maintenance (CBM) of industrial equipment is generally recognized as being the most cost-effective means for improving equipment availability. However, a prerequisite to successful implementation of CBM is a reliable detector of failing components. One such detector, termed the effective negative-sequence impedance, had previously been identified as an indicator of an induction motor stator winding degradation. However, a limitation of this detector is that it may not change in a predictable manner for extremely low levels of deterioration. Presented in this paper is an experimental investigation of a technique for online detection of induction motor stator winding degradation that addresses this difficulty. It begins with a brief description of the detectors, followed by a detailed description of the experimental setup, the experiments conducted, and results.

An overview of fault monitoring and diagnosis in mining equipment

Proper detection and diagnosis of failing system components is crucial to efficient mining operations. However, the harsh mining environment offers special challenges to these types of actions. The atmosphere is damp, dirty, and potentially explosive, and equipment is located in confined areas far from shop facilities. These conditions, coupled with the increasing cost of downtime and complexity of mining equipment, have forced researchers and operators to investigate alternatives for improving equipment maintainability. This paper surveys monitoring and diagnosis technologies that offer opportunities for improving equipment availability in mining. Expert systems, model-based approaches, and neural nets are each discussed in the context of fault detection and diagnosis. The paper concludes with a comparative discussion summarizing the advantages and disadvantages of each. >

Detection of A-C machine winding deterioration using electrically excited vibrations

Presented in this paper is a theoretical review of the relationships that should exist between electrical winding parameters and the mechanical vibration of AC machine elements under normal and faulted operating conditions. Also included is data from an experimental study that relates stator vibration and bearing vibration to selected winding faults in a synchronous machine. Consideration of these results indicates a significant relationship between electrical deterioration and mechanical vibration and thus provides the motivation for additional study and a basis for future applications.

Condition monitoring of induction motor stator windings using electrically excited vibrations

A study designed to investigate the effects of stator winding deterioration on the frequency spectra of mechanical vibration in induction machines is presented. Theoretical motivation for this condition monitoring approach is provided and experimental observations of bearing vibration are presented to provide verification. Results of the study show that specific vibration frequencies may be monitored in order to provide an assessment of stator winding integrity. This information may be used by maintenance personnel as an aid in distinguishing between electrical and mechanical problems or as supporting data for identifying electrical winding breakdown before it progresses to a catastrophic failure. Advantages of this approach are that it has the potential to provide information related to the air-gap flux created by winding deterioration that may not be readily available from voltage and current monitoring and that it is an easily-implemented procedure that may be used to supplement other monitoring techniques.

Condition-based maintenance of electrical machines

Twenty-five years ago, the former US Bureau of Mines funded a research project aimed at developing the enabling technology for incipient failure prediction in electric power system components as a means of reducing the injuries and fatalities that sometimes occur when equipment malfunctions. Over the ensuing years, interest in this has waxed and waned, but interest has been growing for both civilian and military applications. This paper addresses the level of turn-to-turn insulation deterioration that can be resolved using an on-line monitoring technique. The detection of turn-to-turn defects is especially important because they are believed to represent the beginning stage of most motor winding failures.