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There has been active research on motor current signature analysis (MCSA) for over the last 30+ years, as it can provide remote monitoring of rotor and load defects using the current sensor available in the motor control center. However, many years of experience has shown that 1) rotor eccentricity and load defects cannot be distinguished and 2) false rotor cage fault indications are common in the field. There is a recent trend toward integrating “smart” self-diagnostics in electric machines through embedded sensors, especially in applications such as submersible pumps or nuclear plants where motor inspection is difficult. The objective of this article is to evaluate airgap flux measurement as an option for providing sensitive and reliable monitoring of motor and load defects. A new method based on the analysis of the airgap flux search coil voltage during motor starting is proposed for reliable detection and classification of rotor cage, eccentricity, and mechanical defects in the load. Experimental testing is provided to verify the claims made on the proposed method, for cases where MCSA fails.

Detection of rotor cage faults in induction motors based on motor current signature analysis (MCSA) is being extensively applied in the field for preventing forced outage of the motor and industrial process. Although MCSA is very effective for detecting broken bars that are adjacent to each other, it can fail if the broken bars are nonadjacent, which is common for applications with frequent starts. If multiple broken bars are spread out at locations where the rotor “electrical” asymmetry is canceled, the presence of broken bars is difficult to detect with MCSA. A false indication can lead to a catastrophic-forced outage, but the only known means of detecting this type of fault in the field is through rotor visual inspection. In this article, the feasibility of detecting nonadjacent broken rotor bars from the rotor rotational frequency sideband components in the internal and external search coil measurements during steady state and motor starting is evaluated. Experimental testing on a 7.5-hp induction motor shows that nonadjacent broken bars can be reliably detected from the analysis of flux measurements for cases where MCSA and all other electrical tests fail.

The damper (or amortisseur) winding of synchronous motors (SMs) is a critical component required for starting the motor. Several cases of the forced outage of industrial processes due to the starting failure of salient-pole SMs caused by damper bar failure have recently been reported. The detection of broken damper bars is difficult since they are active only during rotor acceleration, and offline visual inspection is the only means of testing available in the field. It was recently shown that the broken damper bars can be detected from the airgap flux, but this requires the installation of airgap flux sensors inside the motor. In this article, a method based on the analysis of the stator starting current is proposed for detecting broken damper bars. In addition, an electrical detection method based on signal injection from the motor terminals is proposed. The new methods have been devised to provide remote testing from the motor control center without motor disassembly required in existing tests. Finite-element analysis (1 MW) and experimental testing (30 kW) performed on salient-pole SMs with emulated broken damper bars show that the proposed methods can provide the sensitive and reliable detection of damper bar failures.

Detection of rotor cage faults in induction motors based on motor current signature analysis (MCSA) is being extensively applied in the field for preventing forced outage of the motor and industrial process. Although MCSA is very effective for detecting broken bars that are adjacent to each other, it can fail if the broken bars are non-adjacent, which is common for applications with frequent starts. If multiple broken bars are spread out at locations where the rotor "electrical" asymmetry is canceled, the presence of broken bars is difficult to detect with MCSA. A false indication can lead to a catastrophic forced outage, but the only known means of detecting this type of fault in the field is through rotor visual inspection. In this paper, the feasibility of detecting non-adjacent broken rotor bars from the rotor rotational frequency sideband components in the internal and external flux measurements during steady state and motor starting is evaluated. Experimental testing on a 7.5 hp induction motor shows that non-adjacent broken bars can be reliably detected from the analysis of flux measurements for cases where MCSA and all other electrical tests fail.

The damper (or amortisseur) winding of synchronous motors (SM) is a critical component required for starting the motor. Several cases of forced outage of industrial processes due to starting failure of salient pole SMs caused by damper bar damage have recently been reported. Detection of damper bar failure is difficult since they are active only during motor starting, and testing in the field currently relies on off-line visual inspection. It was recently shown that broken damper bars can be detected from the airgap flux, but this requires installation of airgap flux sensors inside the motor. In this paper, a method based on analysis of the stator starting current is proposed for detecting broken damper bars. In addition, an electrical detection method based on signal injection from the motor terminals is proposed. The new methods have been devised to provide remote testing from the motor control center without motor disassembly required in existing tests. Experimental testing performed on a 30 kW salient pole SM prototype with emulated broken bars shows that the proposed methods can provide sensitive and reliable detection of damper bar failures.