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It is common practice in the industry for electrical workers to be exposed to shock and arc blast and arc flash hazards as they perform routine maintenance and diagnostic testing on equipment enclosed in motor control centers (MCCs). This paper will illustrate the influence that various IEEE conferences, including the Electrical Safety Workshop, has had on changing the electrical safety culture related to equipment diagnostics. End users are now requesting manufacturers of low- and medium-voltage MCCs to develop or add features and functionality into their products that enhance the ability of electrical maintenance and operating personnel to conduct routine diagnostic and troubleshooting tasks without being directly exposed to energized electrical equipment. This paper will explore some of these features and provide some examples of routine maintenance and diagnostic tasks that can be performed while doing troubleshooting and diagnostic tasks on operating equipment without opening enclosure doors and exposing workers to the hazards associated with exposed energized equipment. [ABSTRACT FROM PUBLISHER]

This paper will demonstrate, through industrial case histories, the application of current signature analysis (CSA) technology to reliably diagnose rotor winding problems in squirrel-cage motors. Many traditional CSA methods result in false alarms and/or misdiagnosis of healthy machines due to the presence of current components in the broken cage winding frequency domain, which are not the result of such defects. Such components can result from operating conditions, motor design, and drive components such as mechanical load fluctuations, speed-reducing gearboxes, etc. Due to theoretical advancements, it is now possible to predict many of these current components, thus making CSA testing less error prone and therefore a much more reliable technology. Reliable detection of the inception of broken cage winding problems, or broken rotor bars, prior to failure allows for remedial actions to be taken to avoid significant costs associated with consequential motor component damage and unplanned downtime associated with such in-service failures. [ABSTRACT FROM AUTHOR]

With the increase in electrified traction applications, high-performance electric motor drives are now frequently coupled to gear transmissions in vehicles. It is appropriate to note that these drives have the capability to be used as a built-in sensor to estimate important characteristics of the mechanical system. The techniques to do this proposed in this paper do not require any change in the motor drive sensors and can be performed in real time during continuously changing conditions. By estimating the states of each element as a function of its position, spatial synchronous averaging can be used on each element to identify its unique characteristics, including deterioration. This paper presents the development and evaluation of these technologies and an exploration of the limitations of the proposed technologies. [ABSTRACT FROM PUBLISHER]

It is well known in the market that the copper rotor motor can give good efficiency at par with the new era motors, and can handle higher temperatures to qualify for electric vehicle application. Being a heavy metal, die-cast copper rotor manufacturing needs absolute care for faithful rotor production. In this paper, the common faults in copper die-cast processing are identified and sufficient monitoring methods are suggested in a three-stage inspection. The final stage consists of a rotor quality test system, which detects most of the problems found in copper die-cast rotors. This rotor quality test system analysis helps to optimize the rotor manufacturing process and avoid the circumstances of fitting an inferior rotor in the motor assembly. [ABSTRACT FROM PUBLISHER]

It is difficult to apply conventional online motor current signature analysis techniques for diagnosis of rotor faults for closed-loop induction motor drives for many applications due to the masking effect of the feedback current controller and/or variable frequency or load operation. Relying solely on traditional offline inspection techniques during regular maintenance does not allow frequent monitoring of rotor problems and is inconvenient since it requires rotor disassembly and/or manual rotor rotation. In this paper, a new automated technique for testing voltage source inverter-fed squirrel-cage induction machines at a standstill for rotor faults is proposed. The main concept is to use the inverter to excite the machine with a pulsating field at a number of angular positions to observe the variation in the impedance pattern due to broken rotor bars, whenever the motor is stopped. An experimental study on a 7.5-hp induction motor verifies that broken bars can be detected with high sensitivity and reliability. It will be shown that the proposed method can provide automated and reliable assessment of rotor condition frequently without motor disassembly, manual rotation, or additional instrumentation. The proposed test can also provide rotor quality assessment independent of variations in motor or load operating conditions since it is a standstill test. [ABSTRACT FROM AUTHOR]

Localized heating caused by damage in the laminations or interlaminar insulation of the stator core increases the core losses and can lead to machine failure. Therefore, it is important to monitor the quality of the stator core for reliable and efficient operation of the machine. The methods currently available for core quality assessment are inconvenient since they require an outage and the machine to be disassembled or operated under no-load conditions. In this paper, a new method for monitoring the quality of the stator core for inverter-fed machines without motor disassembly or operation is proposed. The main concept is to use the inverter to apply a set of test signals to assess the quality of the core whenever the motor is at standstill. A set of high-frequency pulsating magnetic fields is produced using the inverter, and the power loss is observed as a function of field circumferential position to detect core problems. An experimental study on a 10-hp induction motor verifies that local interlaminar core faults can be detected with high sensitivity. The proposed technique is expected to provide a simple solution for frequent stator-core quality assessment without motor disassembly, motor operation, or additional hardware for reliable and efficient operation of inverter-fed induction machines. [ABSTRACT FROM AUTHOR]

Gears form a critical part of many electromechanical systems. Since gear faults cause vibrations, and vibration-based diagnostics are very reliable, this has traditionally been the most commonly used approach to detecting gear faults. However, it is expensive due to the use of high-priced accelerometers and sensor wiring. This paper proposes an alternative way of detecting faults in gears coupled to brushless dc motors by monitoring either the motor current or voltage. It will be shown that gear faults create unique spectral components in the voltage and current spectrums. The faults investigated include damage to gear teeth and loss of lubrication. Experimental and simulation results demonstrate that motor current/voltage signature analysis is a viable tool to detect these gear faults and is a cheaper alternative than vibration-based fault-detection scheme. [ABSTRACT FROM AUTHOR]

The monitoring of airgap eccentricity for induction motors is important for guaranteeing motor reliability, since eccentricity can eventually lead to motor failure due to stator–rotor contact. However, there are many limitations to applying existing test methods such as the motor current signature analysis in the field, particularly for variable frequency applications. In this paper, a new inverter-embedded test approach for detecting eccentricity for induction motors is proposed. The main concept is to use the inverter to perform a standstill test whenever the motor is stopped, to extract information on motor eccentricity. The motor is excited with a low-frequency pulsating ac field superimposed on different levels of dc fields, and the variation in the differential inductance pattern due to the change in the degree of magnetic saturation caused by eccentricity is observed. An experimental study on a 7.5-Hp induction motor under controlled eccentricity conditions verifies that the sensitivity of eccentricity detection can be significantly improved compared with existing methods. [ABSTRACT FROM PUBLISHER]

Rotor axial air ducts are used in large motors for cooling and for reducing weight and material. The rotor axial ducts can produce twice-slip-frequency (2sfs) components in the vibration or a current spectrum that can be misinterpreted as induction-motor rotor faults. There is currently no practical solution to the air-duct-induced false positive indications, which is an ongoing problem in the field. However, there are only a few publications that report the issues caused by rotor axial ducts. In this paper, the influence of the rotor air ducts on motor condition monitoring is analyzed and investigated through testing in the field on 6.6-kV motors and in the laboratory. The experimental study shows that the magnitude of the 2sfs component due to axial ducts depend on the design, material, construction, and operating conditions of the motor. It is also shown that the 2sfs component can even decrease with broken bars, depending on the fault position relative to the ducts, which makes online condition monitoring difficult. Guidelines for reliable motor testing and interpretation of test results are also provided. [ABSTRACT FROM AUTHOR]

There are many limitations to applying online spectrum analysis techniques for diagnosis of closed-loop inverter-fed induction motors due to variable load or frequency operation, and the masking effect of the current regulator. In this paper, a new automated approach for testing inverter-fed induction machines for airgap eccentricity is proposed. The main concept is to use the inverter to excite the machine with a pulsating field at multiple angular positions to observe the variation of equivalent impedance due to eccentricity, whenever the motor is stopped. It is shown that the increase in the value of the equivalent (leakage) inductance under standstill excitation can be used as an indicator of increasing airgap eccentricity. Standstill testing can provide reliable assessment of eccentricity that is independent of variations in operating conditions, load interferences, or motor type. An experimental study on a 7.5-hp induction motor verifies that eccentricity can be detected with high sensitivity and reliability without additional hardware. [ABSTRACT FROM PUBLISHER]

Demagnetization of permanent magnets (PMs) used in synchronous motors can occur due to a combination of thermal, electrical, and/or environmental operating stresses. Since PM demagnetization results in degradation of motor performance, efficiency, and reliability, it is important to monitor the quality of PMs regularly. However, there are many limitations to the offline and online methods currently used for magnet quality assessment. In this paper, a new inverter-embedded technique for automated monitoring of magnet quality for permanent-magnet synchronous motors (PMSMs), which overcomes the limitations of existing techniques, is proposed. The main concept is to use the inverter to perform a standstill test whenever the motor is stopped to detect local or uniform PM demagnetization. The machine is excited with a pulsating field at different angular positions, and the change in the current peaks caused by the change in the degree of magnetic saturation due to demagnetization is observed. An experimental study on a 10-hp PMSM verifies that local and uniform PM demagnetizations can be detected with high sensitivity. [ABSTRACT FROM AUTHOR]

The lifetime of the stator winding insulation is reduced when operated with pulsewidth-modulation inverters, since insulation degradation is accelerated due to increased thermal and electrical stresses on the motor. This paper focuses on a new approach for monitoring the condition of the stator insulation for failure-prone inverter-fed machines. The main concept of the proposed technique is to apply a dc and/or variable-frequency ac test voltage to the stator insulation using the inverter and to perform standard offline insulation tests whenever the motor is not operating. This allows the stator insulation to be tested more frequently as compared to offline tests performed once every three to six years during periodic maintenance. Two methods for testing the insulation with minimal modifications to the inverter circuit are proposed and verified experimentally. The results show that the proposed technique provides a simple low-cost solution for detecting stator insulation degradation at an early stage for reliable operation of inverter-fed machine systems, since the insulation condition can be monitored frequently. This does not only helps prevent forced outages and safety risks due to insulation breakdown but also helps perform maintenance in an efficient manner, since individual motor maintenance can be prioritized and scheduled based on its present condition. [ABSTRACT FROM AUTHOR]

The switched reluctance drive is known to be fault tolerant, but it is not fault free. This paper takes an in-depth look at winding short circuits in this particular machine. Modeling and testing complement a theoretical analysis. Two cases need to be distinguished, one where a complete pole is shorted, and one where a few turns are shorted. Pole short circuits lead to torque reduction that can be easily compensated for with increased current. With few turns shorted, the impact on overall torque may actually be negligible, however, significant currents may circulate through the shorted turns, the worst case being with a single turn shorted with a zero resistance. These results are discussed with a view toward possible remediation schemes aside from simply turning off the faulted phase. [ABSTRACT FROM AUTHOR]

This paper addresses the subject of stator fault diagnosis in direct torque control (DTC) induction motor drives. The particularities of the behavior of a DTC drive, when in the presence of inter-turn short circuits, are exploited, thus allowing the proposal of two different approaches for the diagnosis of this type of fault One of the proposed diagnostic techniques is the well known motor current spectrum analysis. It is demonstrated that in a DTC induction motor drive, with stator inter-turn short circuits, the action of the torque and flux controllers introduce a strong third harmonic in the motor supply currents, which can be used to detect this type of fault. The other diagnostic technique is based on the multiple reference frames theory, recently proposed by the authors for the diagnosis of stator faults in line-connected motors. Here, its use is exploited in the diagnosis of stator faults in DTC induction motor drives. [ABSTRACT FROM AUTHOR]

Motor current signature analysis (MCSA) has recently become widespread in industry for on-line detection of rotor cage faults in induction motors for preventing forced outages. Although it can provide low cost remote monitoring of rotor faults, cases of false indications have been reported, where the causes of some false indications are still unknown. It is shown for the first time in this work that high-amplitude blade pass frequency (BPF) vibrations produced in pumps, fans, or compressors can cause false rotor fault indications if the number of motor poles is an integer multiple of the number of blades. The influence of BPF vibration on MCSA-based rotor fault detection is analyzed, and it is shown that the interaction between BPF vibration and rotor faults can produce false positive and negative fault indications. Alternative test methods capable of separating the influence of the BPF vibration and rotor faults are suggested for avoiding false MCSA alarms. The claims made in the paper are verified experimentally on a custom-built 380 V induction motor-centrifugal pump system setup. [ABSTRACT FROM PUBLISHER]

A high-resistance (R) connection in an induction-motor electrical circuit results in localized overheating and supply-voltage unbalance, which leads to a decreased efficiency and reliability and an increased fire hazard in the electrical distribution system and motor. Therefore, it is important to monitor and correct high-R connections for a reliable, efficient, and safe operation of the industrial facility. This paper focuses on the development of an online technique for detecting poor connections based on monitoring the asymmetry in the voltage and current measurement. The development of the technique begins with the derivation of the dynamic model of an induction motor with high-R connections. Based on the analysis of the model, two approaches for detecting poor contacts using the negative-sequence current and zero-sequence voltage are proposed. In addition to detecting the existence of faults, the location and severity of the fault can also be determined using the proposed method. An experimental study on a 10-hp induction machine under simulated and realistic high-R conditions shows that the proposed techniques provide a simple low-cost solution for reliably detecting poor contact problems at an early stage. It is also shown that the severity and location of the high-R contact fault can be assessed with high accuracy. [ABSTRACT FROM AUTHOR]

The goal of stator-winding turn-fault (TF) detection is to detect the fault at an early stage and shut down the machine immediately to prevent catastrophic motor failure due to the large fault current. A number of TF detection techniques have been proposed; however, there is currently no method available for distinguishing TFs from high-resistance (R) connections (HRCs), which also result in three-phase system asymmetry. It is important to distinguish the two faults, since an HRC does not necessarily require immediate motor shutdown. In this paper, new sensorless online monitoring techniques for detecting and classifying stator TFs and high-R electrical connections in induction machines based on the zero-sequence voltage or negative-sequence current measurements are proposed. An experimental study on a 10-hp induction motor performed under simulated TFs and high-R circuit conditions verifies that the two faults can be reliably detected and classified. The proposed technique helps improve the reliability, efficiency, and safety of the motor system and industrial plant and also allows maintenance to be performed in a more efficient manner, since the course of action can be determined based on the type and severity of the fault. [ABSTRACT FROM AUTHOR]

Future ship integrated power systems (IPSs) will be characterized by complex topologies of advanced power electronics and other evolving components. Advanced capabilities, such as intelligent reconfiguration of system function and connectivity will be possible; however, system level knowledge of component failure will be needed for intelligent power distribution under failure mode conditions. Diagnostic and prognostic coverage for sensors, components, and subsystems will be essential for achieving reliability goals. This paper will look at some diagnostic requirements and emerging technologies available for insertion into future ship IPSs. [ABSTRACT FROM AUTHOR]

Ferromagnetic materials may be affected by the presence of local losses due to defects or magnetic anomalies caused by machining processes. To highlight such anomalies is not easy; a noninvasive thermographic method has been refined to allow a proper comparison of different machining processes’ impact on the iron losses. Specimens obtained with punching, wire erosion, and laser cut have been analyzed using a high-speed IR camera when subjected to alternate magnetization at different frequencies. Also, the same technique has been adopted to the assembled stacks to investigate more simultaneous phenomena. The possibility to point out localized anomalies should be exploited to foresee and avoid electrical machines core faults. [ABSTRACT FROM AUTHOR]

A new preventive maintenance strategy for the sensorless condition monitoring of inverter dc-link aluminum electrolytic capacitors based on equivalent series resistance (ESR) and capacitance C estimation is proposed. The main concept of the proposed method is to estimate the ESR and C of the capacitor, using the inverter whenever the motor is stopped. The parameters are estimated from the dc-link voltage and stator current measurements available in the inverter with the switched dc-link voltage applied to the motor stator winding. The temperature of the capacitor can also be estimated under thermal equilibrium based on the stator resistance estimate to take the influence of temperature variation into account. An experimental study on a 250-W permanent magnet synchronous motor performed under accelerated capacitor degradation is presented to verify the pro- posed technique. It is shown that the proposed method provides a reliable and sensitive indication of capacitor aging without additional hardware requirements for reliable, efficient, and safe operation of the inverter and driven process. [ABSTRACT FROM AUTHOR]

Electromagnetic devices may be affected by the presence of local losses due to material defects or magnetic anomalies caused by mechanical processing. The localization of such defects is the main goal of this article; a noninvasive method has been pursued to perform the inspection and detection of imperfections or defects. The adopted approach is based on the observation of the device under test with a high-speed IR camera; no limitations in size and shapes devices are considered and the method can be widely adopted. Examples of defects detection in the magnetic circuit realization are proposed, both for traditional ferromagnetic laminated sheets and for soft magnetic composites. [ABSTRACT FROM AUTHOR]