Chanseung Yang

Advanced Induction Motor Rotor Fault Diagnosis Via Continuous and Discrete Time–Frequency Tools

Transient-based fault diagnosis in induction motors has gained increasing attention over the recent years. This is due to its ability to avoid eventual wrong diagnostics of the conventional motor current signature analysis in certain industrial situations (presence of load toque oscillations, light loading conditions, and so on). However, the application of these transient methodologies requires the use of advanced signal processing tools. This paper presents a detailed comparison between the two main groups of transforms that are employed in transient analysis: discrete and continuous. This paper does not focus on trivial fault cases but on difficult real situations where the application of the conventional methods often leads to false diagnostics (outer bar breakages in double-cage motors, motors with rotor axial duct influence, and combined faults). Indeed, it is the first time that continuous tools are applied to some of these controversial situations. The results in this paper prove the special advantages of the continuous transforms, tearing down some false myths about their use.

Reliable Detection of Induction Motor Rotor Faults Under the Rotor Axial Air Duct Influence

Axial cooling air ducts in the rotor of large induction motors are known to produce magnetic asymmetry and can cause steady-state current or vibration spectrum analysis based fault detection techniques to fail. If the number of axial air ducts and that of poles are identical, frequency components that overlap with that of rotor faults can be produced for healthy motors. False positive rotor fault indication due to axial ducts is a common problem in the field that results in unnecessary maintenance cost. However, there is currently no known test method available for distinguishing rotor faults and false indications due to axial ducts other than offline rotor inspection or testing. Considering that there is no magnetic asymmetry under high slip conditions due to limited flux penetration into the rotor yoke, the detection of broken bars under the start-up transient is investigated in this paper. A wavelet-based detection method is proposed and verified on custom-built lab motors and 6.6-kV motors misdiagnosed with broken bars via steady-state spectrum analysis. It is shown that the proposed method provides the reliable detection of broken bars under the start-up transient independent of axial duct influence.

Screening of False Induction Motor Fault Alarms Produced by Axial Air Ducts Based on the Space-Harmonic-Induced Current Components

Motor current signature analysis (MCSA) based on the 50/60-Hz sidebands has become a common test in industry for monitoring the condition of the induction motor rotor cage. However, many cases of unnecessary motor inspection or outage due to false alarms produced by rotor axial duct interference have been reported. If the number of axial ducts and poles is identical, this can produce 50/60-Hz sideband frequency components in MCSA that overlap with that of rotor faults, resulting in false alarms. However, there currently is no practical test method available for distinguishing rotor faults and false indications other than testing the rotor offline or under the startup transient. In this paper, the feasibility of using the rotor fault frequency component produced by the space harmonic waves is evaluated as a solution for the first time. Since the fifth or seventh space harmonics have a spatial distribution of flux that does not penetrate in the rotor yoke to reach the axial ducts, they do not produce false alarms. The proposed method is verified on 6.6-kV motors misdiagnosed with broken bars via the 50/60-Hz sidebands of MCSA. It is shown that it provides reliable online indication of rotor faults independent of axial duct influence and can be used for screening out false alarms.

On Mass Concentration for the L 2-Critical Nonlinear Schrödinger Equations

We consider the mass concentration phenomenon for the L 2-critical nonlinear Schrödinger equations. We show the mass concentration of blow-up solutions contained in space near the finite time. The new ingredient in this paper is a refinement of Strichartzs estimates with the mixed norm for 2 < q ≤ r.

On mass concentration for the L2-critical nonlinear schrodinger equations

We consider the mass concentration phenomenon for the L 2-critical nonlinear Schrödinger equations. We show the mass concentration of blow-up solutions contained in space near the finite time. The new ingredient in this paper is a refinement of Strichartzs estimates with the mixed norm for 2 < q ≤ r.

Use of discrete and optimized continuous TFD tools for transient-based diagnosis in controversial fault cases

Transient-based diagnosis of electromechanical failures in induction motors has gained an increasing attention over recent years. The diagnostic in some specific situations (presence of load toque oscillations, light loading conditions) or of specific failures may be difficult when using the classical MCSA approach. In this context, the transient-based methodologies have been proven to become valuable informational sources for the diagnosis, either confirming the MCSA results or avoiding its possible false positives. The application of these transient methodologies requires the use of modern signal processing tools that are in continuous evolution. This work proposes the application of an advanced tool; the recently developed Adaptive Slope Transform. The paper compares the performance of this continuous transform and that of a discrete counterpart, the Discrete Wavelet Transform, when applied to different controversial fault cases in which the classical MCSA may not lead to correct results: outer bar breakages in double cage motors and motors with rotor axial duct influence. The results show the potential of the continuous transforms for the transient tracking of high-order fault-related components as well as for the improved discrimination between fault components.

Starting current analysis for condition monitoring of medium voltage induction motors in the steel industry

Failure of medium voltage (MV) induction motors is a major concern in the steel industry considering that it can cause an unplanned outage of the process resulting in significant economic consequences. Predictive maintenance based on offline and on-line testing of the induction motors is therefore critical for maintaining reliable, efficient, and safe plant operation. Many years of experience has shown that the MV induction motor failure rate can be significantly reduced with periodic motor testing, resulting in improved plant reliability and productivity. It has also been observed that false fault indications are commonly produced by commercially available test equipment, and that applying multiple types of tests can improve the reliability of testing. In this paper, the effectiveness of a new test approach based on the analysis of the motor starting current is investigated for detecting defects in the rotor cage and reactor starting. Analysis of the starting data obtained from 614 MV induction motors operating at a steel mill over the last 10+ years showed that the two types of faults were present in 45 MV motors. 7 successful case studies of rotor cage and reactor starting defects are presented to provide insight on the advantages of starting current analysis for induction motor monitoring.

Electrical monitoring of mechanical defects in induction motor driven V-belt-pulley speed reduction couplings

V-belt-pulley couplings are commonly used for speed reduction in induction motor driven industrial applications since they provide flexible transmission of power at low cost. However, they are susceptible to mechanical defects such as belt wear or crack that can cause slippage or damage of the belt and lead to decrease in efficiency and lifetime of the system. There are many limitations to applying existing tests such as visual inspection, thermal or mechanical monitoring as they require visual or physical access to the system and/or costly sensors. Considering the large quantity of belt-pulley systems employed in industry, the impact of the economic loss incurred by low-efficiency operation and unplanned process outages is significant. In this paper, electrical monitoring of belt-pulley coupling defects based on the analysis and trending of the stator current frequency spectrum under steady-state and starting conditions is presented. The proposed method is verified on 1) 6.6 kV motor driven pulpers, and on a 2) custom-built motor driven air compressor with speed reduction belt-pulleys under controlled fault conditions. It is shown that the proposed method can provide automated, remote, and safe detection of belt-pulley defects based on existing current measurements for improving system reliability and efficiency.

On Mass Concentration for theL2-Critical Nonlinear Schrödinger Equations

We consider the mass concentration phenomenon for the L 2-critical nonlinear Schrödinger equations. We show the mass concentration of blow-up solutions contained in space near the finite time. The new ingredient in this paper is a refinement of Strichartzs estimates with the mixed norm for 2 < q ≤ r.