Induction motor diagnosis using voltage spectrum of an auxiliary winding - time varying load torque

The method consists of inserting an auxiliary small winding which is a coil " sneak " that forms an angle (}o with the A stator phase as it is shown in fig. 1. This coil has no conductive contact with the other phases but it is mutually coupled with all the other circuits on both the stator and rotor sides [10].
I.
differential equations is presented. This leads to the inserted winding voltage and its Park components expressions. Then, a FFT analyzer is required for converting the signals from the time domain to the frequency domain . Simulations are curried out by Matlab software . Their results prove that the spectrum of these voltages associated to the Lissajous curve formed of the voltage Park components show the machine abnormality in the case of a varying load: an oscillating load torque.
Induction Motor Diagnosis Using Voltage Spectrum of an Auxiliary Winding - Time Varying Load Torque
Lamiaa EI Menzhi I, Abdallah Saad 2
IDept. of Physics , Faculty of Sciences Ben Msik Casablanca, Morocco 2Dept. of Electrical Eng., The National School of Electrical and Mechanical Engineering Casablanca, Morocco E-mail: lamdockit@
Therefore: (1) Where:
the simulation results (simulations were curried out for different values of the angle). Therefore, we choose to zero.
00 equals
[A]=-[Lr([R]+ d~~])
c. Auxiliary winding voltage Park components In order to obtain the Park components, we consider two other fictive coils forming with the real coil a three phase system. In this case, the expression of the main voltage as a function of its Park components is:
[V]=([R]+ d[L])[I] + [L]d[I]
dt dt
Fig. 1. Auxiliary winding emplacement inside the induction motor
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V auxa
Where and
=Hபைடு நூலகம்
(Vad COS (8s
lfJad
)-
Vaq sin (8s
))
(6)
dm dt
= P (r -r)
J
e r
(2) (3)
-=01
dO dt
Therefore and
({Jad ({Jaq
II. ANALYSIS OF THE AUXILIARY WINDING VOLTAGE PARK COMPONENTS
INTRODUCTION
Induction motors have been known to have simple and robust construction, as well as very high reliability . Especially, squirrel cage machines are frequently used in variable speed drives with applications ranging robotics , machine tools to railway traction and army applications. However, as many other machines , induction motors can be defected because critical applications are found in all industries[I]: thermal , electrical, mechanical , environmental, dynamic [2]. Induction motor defect can have a direct influence on the factory production system . Since the protection tools work at the last stage of the defect, they can stop neither the electric machines failures nor their consequences. Even using the classical maintenance, it is impossible to detect these defects in most of the cases especially at the machine offline checking. Early detection of abnormalities in the motors will help to avoid expensive failures. Therefore, induction motor monitoring and online diagnosis are necessary. Further and continuing research has led to new techniques for conditioning the current, voltage and instantaneous power signals in order to analyze them and determine the nature of the fault without disturbing the motor operation [3], [4], [5], [6], [7], [8] and [fY]. Among the online diagnostic methods, the one based on the so-called auxiliary winding voltage signal approach, it uses, in fact, the voltage of an auxiliary winding which is a small coil "sneak" inserted between two of the stator phases[IO] . The aim of this paper is to present a new methodology by which induction motors faults related to load torque can be diagnosed . It is based on the Park components of the auxiliary winding voltage. Theoretically, there is no common expression of these voltage components. So first of all, induction motor mathematical model of nonlinear current
A. System mathemat ical model
Experimentally, it is easy to obtain the voltage of this auxiliary winding . However, in the theory, it is necessary to look for a mathematical expression as a function of the main phases currents [10]. The electrical equations for the induction machine can be written in vector matrix form as:
and
[B]= [L]-l[V]