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Electrical Motors


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Electrical Motors Condition Monitoring


by Alexey I. Tadjibaev and Michael P. Tsypkin

Abstract


This paper compares motor current signature analysis & vibration signature analysis techniques on the most common induction motor defects. It would be a good reference for beginning and intermediate analysts and engineers that are looking for additional information comparing different PdM technologies for monitoring induction motors. There are several spectral charts and a table showing the comparisons of the differing technologies. This paper is more practical in showing the results of different monitoring technologies. This paper thoroughly describes the technologies, their applications, and the results. The paper is not intended as a case history but uses real data for the development of the comparisons.

PREVIEW


“Recently a technique known as “Motor Current Signature Analysis” is being offered by several commercial suppliers [1]. Phase current analysis have been implemented for rotor winding faults detection in squirrel cage induction motors very effectively [2]. However, the faults of other parts of the induction motor electromagnetic system very often occur. For example a survey of the induction motors faults [3] demonstrates that motor failures arise from faults in the stator winding take place three times frequently than from faults in the rotor winding. Analysis of the phase current spectrum does not permit to find defects in the stator winding [1]. This method is not universal one for on-line induction motor condition monitoring.

Paper presents comparative analysis of some effective methods for on-line condition monitoring of induction motor electromagnetic system. Any internal incipient fault of the electromagnetic system causes the abnormal operating conditions of the motor (faults which do not cause failure of machine). Such abnormal conditions are investigated more than one hundred years. Goerges [4] was the first to study the operation of three-phase induction motors with asymmetrical rotor circuit. Method of “Symmetrical Components” for analysis of the induction motor with stator and rotor asymmetries was presented, by Wagner C.F. and Evans R.D. [5]. Since then many investigators have studied these problems and many works were published.

Practicing engineer noted in the 30-th years that rotor winding faults cause low frequency vibration and slowly oscillations of amperemeter arrow [6,7]. 

More recently, vibration and current became the fundamental performances for induction motor rotor faults detection, owing to modem measuring technique and instruments [1,8,9,10,12,22]. At the present time some other physical parameters are used for on-line induction motor monitoring too, among them: speed fluctuation [13], leakage flux [15], temperature [14], static and dynamic electrical performances [16].

The condition monitoring methods for on-line induction motor electromagnetic system control by vibration and current spectral analysis are discussed in this paper.

2. On-line induction motor condition monitoring techniques.

Interconnection between different physical processes in the induction motor explains diversity of the condition monitoring methods commonly used. A change in even thought only one construction parameter of the motor (stator and rotor windings resistance, air gap eccentricity, condition of rotor and stator cores) causes a change of practically all physical performances of operating motor (current, magnetic field, vibration and. noise, rotating speed, temperature, torque).

A sensitivity of the measured physical parameter (diagnostic symptom) in reference to the defect quantity is one of the most important indicators.”

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