Thermal Modelling of Induction Machine Using the Lumped Parameter Model

Thermal Modelling of Induction Machine Using the Lumped Parameter Model.

ABSTRACT  

rise is of much concern in the short- and long-term  of induction machine, the most useful industrial icon. This work examines induction machines mean temperatures at the different core parts of the .

The system’s thermal network is developed, the and differential equations for the proposed models are solved so as to ascertain the thermal performances of the machine under steady and transient conditions.

The lumped parameter thermal method is used to estimate the temperature rise in induction machine. This method is achieved using thermal resistances, thermal capacitances and power losses.

To analyze the thermal process, the 7.5kW machine is divided geometrically into a number of lumped components, each component having a bulk thermal storage and heat generation and interconnections to adjacent components through a linear mesh of thermal impedances.

The lumped parameters are derived entirely from dimensional information, the thermal properties of the materials used in the design, and constant heat transfer coefficients.

The thermal circuit in steady-state condition consists of thermal resistances and heat sources connected between the component’s nodes while for transient analysis, the thermal capacitances were used additionally to take into account the change in internal energy of the body with time.

TABLE OF CONTENTS

Title page ………………………………………………………….………………..….iii
Approval page ………………………………………………………………….….…..iv
Certification page………………………………………………………….…..….……v
Dedication page…………………………………………………………….…..….…..vi
Acknowledgement………………………………………………………….…..….….vii
Abstract……………………………………………………………………..…..….….viii
Table of contents…………………………………………………….….……..….……ix
List of figures…………………………………………………………….……..……..xii
List of tables………………………………………………………….…….…..….….xiv
List of symbols…………..……………………………………….……………..……..xv

Chapter One: INTRODUCTION ………………………………………………..….…..1
1.1 Background of study…………….……………….…………………………….…1
1.2 Statement of Problem …………………..……….…………….……….….….…3
1.3 Purpose of Study ………………………………..…………………………………..3
1.4 Significance of Study ………………………………………….………………….4
1.5 Scope of Study..……………………………………….……………………………….5
1.6 Arrangement of Chapters ……..………………………………….……………….5

Chapter Two: LITERATURE REVIEW …………………………….…………………..6

Chapter Three: HEAT TRANSFER MECHANISMS IN ELECTRICAL MACHINES
3.1 Heat Transfer in Electrical Machines…………….……………….….………12
3.2 Modes of Heat Transfer …………………..……………..…….………….…13
3.2.1 Conduction ………………………………………………….……………………14
3.2.2 Convection ……………………………………………………………………..16
3.2.3 Radiation …………………..…………………………………….……………….18
3.3. Heat Flow in Electrical Machines ………………….…………..……..…..…20
3.3.1 Heat Transfer Flow Types …………………………………………………..20
3.3.2 Heat Transfer Flow System …………………………………..……….……..21
3.3.3 The Boundary Layers……………………………………………….…………22
3.4 Determination of Thermal Conductance………………………….….……….23
3.5 Thermal-Electrical Analogous Quantities ………………………….….……25
3.5.1 Thermal and Electrical Resistance Relationship …………….….…..…….26

Chapter Four: THERMAL MODEL DEVELOPMENT AND PARAMETER COMPUTATION
4.1 Cylindrical Component and Heat Transfer Analysis…………….……………28
4.2 Conductive Heat Transfer Analysis in Induction Motor ………….…….……28
4.3 Convective Heat Transfer Analysis in Induction Motor………….…….…….34
4.4 Description of Model Components and Assumptions …………….…….….35
4.5 Calculation of Thermal Resistances…………………………….…………….45
4.6 Calculation of Thermal Capacitances ………………………..…………….…56

Chapter Five: LOSSES IN INDUCTION MACHINE
5.1 Determination of Losses in Induction Motors .…………………….………..69
5.1.1 Stator and Rotor Copper Losses ……………………..…………….…….. 69
5.1.2 Core Losses …………………………………………….…….……..….……70
5.1.3 Friction and Windage Losses ………………………….………..………….70
5.1.4 Differential Flux Densities and Eddy-Currents in the Rotor Bars ………..71
5.1.5 Stray-Load Losses …………………………………………………………….72
5.1.6 Rotor Copper Losses …………………………………………………….……72
5.1.7 No Load Losses …………………………………………….…………….…..73
5.1.8 Pulsation Losses ………………………………………………………………74
5.2 Calculation of Losses from IM Equivalent Circuit…………………………..74
5.3 Loss Estimation of the 7.5 kW Induction machine ….….………………….79
5.4 Segregation and Analysis of the IM Losses……… ………………………..82
5.5 Performance Characteristics of the 10 HP Induction machine…..………..83
5.6.1 Motor Efficiency /Losses ……………………….…………………………….86
5.6.2 Determination of Motor Efficiency ……………………..………….………….86 5.6.3
Improving Efficiency by Minimizing Watts Losses …………………………87
5.7 The Effects of Temperature ……………………………..….…….…………..88

Chapter Six: THERMAL MODELLING AND COMPUTER SIMULATION
6.1 The Heat Balance Equations ……………………………………………….……90
6.2 Thermal Models and Network Theory ……………………………….……..…90
6.3 The Transient State Analysis ……………………………….………….………98
6.4 The Steady State Analysis …………………………………………………..104
6.5 Transient State Analysis results.………………….….………………..……..108
6.6 Discussion of Results …………………………….……………………..…….116

Chapter Seven: CONCLUSION AND RECOMMENDATION
7.1 Conclusion…………………….……………….….……………………..…….118
7.2 Recommendation …………….………………….……………………..…….119

REFERENCES …………………………………………………………………..…..….…..120
APPENDIX………………………………………………..……………….……..……….…..131

INTRODUCTION  

This thesis is concerned with the thermal modelling of the induction machine. With the increasing quest for miniaturization, energy conservation and efficiency, cost reduction, as well as the imperative to exploit easier and available topologies and materials, it becomes necessary to analyze the induction machine thermal circuit to the same tone as its electromagnetic design.

This would help in achieving an early diagnosis of thermo-electrical faults in induction machines, leading to an extensively investigated task which pays back in cost and maintenance savings.

Since failures in induction machines occur as a result of aging of the machine itself or from severe operating conditions then, monitoring the machine’s thermal condition becomes crucial so as to detect any fault at an early stage thereby eliminating catastrophic machine faults and avoidance of expensive maintenance costs.

Faults in induction machines can be broadly classified into thermal faults, electrical faults and mechanical faults. Currently, stator electrical faults are mitigated by recent improvements in the design and manufacture of stator windings.

However, in case of machine driven by switching power converters the machine is stressed by voltages including high harmonic contents. The latter option is becoming the standard for electric drives. A solution is the development of vastly improved thermal system cum insulation material. 

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StudentsandScholarship Team.