Subrata Karmakar

Novel diagnosis technique of mass unbalance in rotor of induction motor by the analysis of motor starting current at no load through wavelet transform

This paper presents an improved technique for detection of mass unbalance in rotor of an induction motor by the analysis of transient stator current during starting period using both discrete wavelet transform (DWT) and continuous wavelet transform(CWT). The unbalanced magnetic pull due to centrifugal force developed for mass unbalance in rotor produces excessive vibration in the rotor as well as in the stator, resulting changes in air gap flux distribution which induces voltage in the rotor and in the stator and generation of unique signature pattern in the stator current. During starting, unbalanced magnetic pull is very high, the rotor is pulled across the whole air gap which increases the amplitudes level of the harmonics already present and generation of new harmonics due to this fault in the stator current. In the present paper, the starting current at no load is captured and analysed for diagnosing the motor fault. As motor current signature (MCS) significantly depends on loading condition of the induction motor during steady state, the detection of faults using MCS at no load or light load by FFT technique is difficult. This has been overcome by this proposed improved technique as motor current does not depend on load and is very high even at no load during starting. This technique has been developed and implemented in the laboratory using machine fault simulator.

Induction Motor and Faults

The chapter deals with general description of an induction motor followed by different faults. First, construction of induction motor has been discussed. Then a review of induction motor fault has been presented. Faults like rotor broken bar, mass unbalance, stator faults, single phasing, crawling, bearing faults, etc. are discussed along with causes and effects.

Single Phasing of an Induction Motor

This chapter deals with the diagnosis of single phasing fault in induction motor. Motor current signature analysis (MCSA ) technique has been discussed. Phase angle shift is assessed at single phasing . Steady-state current Concordia is formed and assessed by feature pattern extraction method (FPEM ). Then, radar analysis of line currents and those Concordia during normal and single phasing are discussed.

Crawling of an Induction Motor

This chapter deals with the assessment of crawling . The assessment is done in Park plane . Steady-state stator currents are transformed into Park plane. Concordia is formed in the Park plane. Presence of 7th harmonics is assessed by the feature pattern extraction method (FPEM ) and the CMS rule set used for harmonic assessment in Park plane from where crawling is detected.

Induction Motor Fault Diagnosis: General Discussion and Research Scope

This chapter deals with general discussion and research scope on induction motor fault diagnosis. Fault considered in the book and analytical tools used for motor fault diagnosis has been listed. Then, general discussion on induction motor fault diagnosis has been made. At last research scope in this field has been highlighted.

Analytical Tools for Motor Fault Diagnosis

This chapter deals with different approaches useful for motor fault diagnosis. It mentions different methods like thermal analysis, acoustics analysis, vibration analysis, etc. Then, mathematical tools used for signal processing and analysis of steady as well as transient currents are discussed. It covers fast Fourier transform (FFT), wavelet transform (WT), discrete wavelet transform (DWT), Concordia, radar analysis, etc.

Stator Winding Fault

The chapter deals with stator winding faults. Assessments of different types of stator winding fault are discussed in this chapter. Both steady-state and transient current-based diagnosis are covered. Sequence component-based stator fault diagnosis is presented. Park plane is sometime used for fault diagnosis. Different wavelet transformation techniques are used for stator fault diagnosis.

Rotor Mass Unbalance

The chapter deals with rotor mass unbalance fault. Diagnosis is done both using steady-state signal as well as starting current transients. Concordia is formed using steady-state current and analyzed. The Concordia -based assessment is done using starting current transients. Then radars are formed in Park plane wherefrom the faults are differentiated compared with those of normal motor. Then harmonics generated due to rotor broken bar has been assessed using FFT and wavelet transforms .

Broken Rotor Bar

The chapter deals with broken rotor bar fault. Diagnosis is done both using steady-state signal as well as starting current transients. Concordia is formed in Park plane using steady-state current and analyzed. The Concordia-based assessment is done in Park Plane using starting current transients. Then radars are formed in Park plane wherefrom the faults are differentiated compared with those of normal motor. Then harmonics generated due to rotor broken bar has been assessed using Hilbert and wavelet transforms. The main contribution in this chapter is the application of new fault diagnostic concept based on radar assessment and envelope analysis to extract low-frequency oscillation using Hilbert and wavelet transforms.