Study of Eccentricity in a Machine Three-Phase Induction Squirrel-Cage Rotor

Study of eccentricity in a machine three-phase induction squirrel-cage Rotor

Adelino. S. Dantas

10711-MEE-Energia

Instituto Superior de Engenharia

Lisboa, Portugal

[e-mail]

Abstract - the efficient electric machine for which it was designed with a view to removing its best performance is a very important aspect. This article describes the analysis of the effects of eccentricity of induction machine and its effects on the torque. This theme is of great importance for diagnosis of malfunctions. This analysis will be made by the finite element method. This document also presents the study of effect of rotor eccentricity in three distinct schemes, stationary, dynamic and mixed, allowing thus a comparison between them and the observed effects on the position of the rotor and in binary. Analysis of induction machine and will be made with torque rotor centered and comparing with the stationary, dynamic and mixed regimes for following posionamentos of the rotor:

1. Decentered the 25% of the air gap.
2. Decentered to 50% of the air gap.
3. Decentered the 75% of the air gap.

The influence of the binary in the various schemes in an induction machine allows you to diagnose malfunctions of the machine.

 Keywords: induction machine; rotor eccentricity; malfunctions of the rotor; binary; Finite element method.

INTRODUCTION
The aim of this work is to study the influence of a particular defect of eccentricity in an induction machine, in the various regimes of rotor position on stationary, dynamic and mixed. The existence of these problems and malfunctions that lead to destruction of the machine becomes this issue more significant and of great concern in industrial applications.

This study focuses on the analysis of certain parameters of induction machine with different rotor positions.
The objectives of this work are the following:

1. Perform successfully modelling induction machine of squirrel-cage rotor;
2. Get different models for different rotor eccentricity topologies, including static, dynamic and mixed;
3. Addressing the binary behavior before the different machine topologies to eccentricity, having regard to the operation of the machine under static, dynamic and mixed;

Interpret the results obtained.

1. Finite element method

The finite element method (or MEF) is a method of analysis of mathematical models of physical problems in continuous media, based on Maxwell's equations and equations of own materials. When connected, they describe the field equations. Consists in the Division (meshes) of the integration domain in a finite number of small regions (triangles), that are called "finite elements", from a constant domain to a discrete domain [1].

This paper uses the finite element method for the analysis of field, offering in this way a precise evaluation of the distribution of the magnetic field and mechanical performance of the machine. The complex geometry of the stator and rotor lamination with bars in short, as the spatial distribution of drivers into the slots in the stator, and the effect of non-linearity of the magnetic material must be taken into account.

So was the allocation of a finite element mesh whose dimension to the different area of the machine can be observed in table 1.

Zone	Finite element mesh size in mm
Air	0,1
Rotóricas bars	1
Iron	1
Came	0
Windings	1

Table 1-representation of the finite element mesh used in simulations

 

II. Assumptions and modelling of the MACHINE.

Given the topology of the machine, the type of problem used was the planar type, since it assumed that the magnetic phenomena are equal on each plane (x, y) with the zz axis (rotor centered). In this way the effects of the conductors that connect a cava estatórica the other outcasts. In terms of dimensions, the unit used in the modelling of machines was the millimeter (mm). Each simulation was performed for a frequency of 50 Hz mains frequency. Broadly speaking, the machine used it is a three-phase induction machine, 2kW of power. Is composed with a total of 4 poles, 36 estatóricas 28 rotóricas bars and cavas. Each phase is composed with a total of 3 reels (A, B, C). In terms of dimensions, the machine has a diameter of 130 mm and a depth of 100 mm [5].

As you can see in Figure 1, the field lines feature a regular layout, i.e. not present discontinuities nor is there a great density in terms of field as shown. Once a there is no discontinuity points, it can be concluded that the finite element mesh set fits problem. Another aspect is the fact that the field lines don't go out of bounds are representative of the machine, which shows that the boundaries are well defined (Dirichelet).

[pic 3]

Figure 1-centered Rotor; FEMM model

1. Choice of material

The windings estatóricos material is Winding Stator windings surround material estatóricos and rotóricas bars of M-15 steel material. Rotóricas bars material is Alumium and the spindle of the machine and the air gap is Air table 2 [6].

B- Sizing of conductors

Sizing of conductors estatóricos windings. In the scaling of these drivers is important to know some aspects, such as: total area of cava, cava's useful floor area, number of turns for cava, among others. Knowing that each cava possessed a total area of 5.74609 x 10-5 m2, it is possible to know which area of the same. To determine this aspect, it is considered that the area is about 75% of the total area. With this, an area of about 4 x 10-5 m2. Each dig a total of 44 turns and knowing the value of the area, a section of approximately 0.979 mm2/espira. Using a table of a manufacturer of enamelled copper conductors, it was found that the effective current permissible by the driver is 1.89, corresponding to a conductor AWG 17. Once the FEMM only works with maximum currents, the current used in the simulation was of (√ 2 × 1.89) = 2.67A.