Estimating the magnetic characteristics of a salient pole
synchronous machine using ampere turns distribution method
By
Jayaram Subramanian
B.E., Anna University, 2012
A thesis submitted in partial fulfillment of the requirements for the degree of
Master of Applied Science
In the department of Electrical and Computer Engineering
©Jayaram Subramanian 2015
University of Victoria
All rights reserved. This dissertation may not be reproduced in whole or in part, by
photocopying or by other means, without the permission of the author
i
Supervisory Committee
Estimating the magnetic characteristics of a salient pole
synchronous machine using ampere turns distribution method
By
Jayaram Subramanian
B.E., Anna University, 2012
Supervisory Committee
Dr.Subhasis Nandi,
Supervisor (Department of Electrical and Computer Engineering)
Dr.Nikitas Dimopoulos,
Department Member (Department of Electrical and Computer Engineering)
ii
Abstract
Supervisory Committee
Dr.Subhasis Nandi,
Supervisor (Department of Electrical and Computer Engineering)
Dr.Nikitas Dimopoulos,
Department Member (Department of Electrical and Computer Engineering)
Modeling plays a very important role in a variety of applications such as performance
analysis, characterization, fault diagnosis, condition monitoring and stress analysis of electrical
machines. With the importance of modeling of electrical machines increasing day by day,
researchers are striving for better methods to solve the problem. One of the widely used
techniques for modeling electrical machine is the finite element method. As computational
power continues to be less and less expensive, the finite element method is becoming a widely
used technique for modeling of electrical machines because of its advantages in terms of
accuracy and efficiency. Many commercial finite element software packages are now available
for this purpose. One such software, the Ansys Maxwell is used extensively for the modeling of
electrical machines. It is the top of the line finite element package used by many motor
manufacturers for industrial motor design and performance analysis. Ansys Maxwell has specific
features such as the field calculator and RMxprt which facilitates the modeling of electrical
machines. One of the important parameters while modeling electrical machine is the magnetic
iii
characteristics of the core material. This plays a significant role in the performance
characteristics and the analysis of electrical machines. This research work addresses this problem
and provides a simple yet effective solution to determine the average magnetic characteristics of
a salient pole synchronous machine that uses a material for the rotor with unknown magnetic
characteristics. Existing techniques available to determine the magnetic characteristics of a
material are mainly Epstein and single sheet tester. These two tests require a separate sheet of
material and they are destructive. Therefore a non-invasive and non-destructive technique had to
be designed to solve this problem as the manufacturers could not provide the data for the
magnetic material used in the rotor.
In this work, an FE model of the salient pole synchronous machine was developed to
closely emulate the characteristics of the experimental machine. This FE model was first
subjected to magnetostatic simulation under different field currents using a known magnetic
material. By comparing the result with the experimental machine and by performing a technique
named ampere turn distribution technique, a new magnetic material characteristic was developed
to follow the average characteristics of the rotor and the stator. Following the determination of
the new material, this material was used in the simulation of the salient pole synchronous
machine running as a motor and a generator under varying load condition and field currents.
These results were then compared with the real machine to determine the effectiveness of the
developed scheme.
The pursuit of research in this topic led to the following publication:
1. Subramanian, J.; Nandi, S.; Ilamparithi, T.; Winter, O., "Estimating the magnetic
characteristics of a salient pole synchronous machine using ampere turns
distribution
method,"
Electrical
Machines
(ICEM),
2014
International
Conference on , vol., no., pp.1594,1600, 2-5 Sept. 2014
iv
Table of Contents
Supervisory Committee .................................................................................................................. ii
Abstract .......................................................................................................................................... iii
List of Figures .............................................................................................................................. viii
List of Tables ................................................................................................................................. xi
List of Abbreviations ................................................................................................................... xiii
List of symbols ............................................................................................................................. xiv
Chapter 1
Introduction to magnetic measurement techniques in rotating machines ................. 1
1.1
Introduction to modeling of electrical machines .............................................................. 1
1.2
Introduction to measurement techniques of magnetic characteristics of materials in
Electrical machines ..................................................................................................................... 2
1.2.1
Ring Test ................................................................................................................... 3
1.2.2
Epstein Test ............................................................................................................... 4
1.2.3
Single Sheet Test (SST) ............................................................................................ 6
1.2.4
Other Techniques .................................................................................................... 11
1.2.5
Comparison of Epstein and SST techniques ........................................................... 16
1.3
Motivation of the present research work ........................................................................ 16
1.4
Thesis outline ................................................................................................................. 17
Chapter 2
Finite Element Modeling ........................................................................................ 19
2.1
Electromagnetic analysis ................................................................................................ 19
2.2
Finite Element Analysis (FEA): ..................................................................................... 20
2.3
FE in Electrical Machines .............................................................................................. 21
2.4
Commercial FE packages available for Electrical Machines: ........................................ 22
2.5
Ansys: ............................................................................................................................. 23
v
2.5.1
Ansys RMxprt ......................................................................................................... 25
2.5.2
Field Calculator:...................................................................................................... 27
2.5.3
Solvers..................................................................................................................... 28
2.5.4
Material Properties .................................................................................................. 31
2.6
Conclusion...................................................................................................................... 33
Chapter 3
3.1
Ampere Turn Distribution Scheme ......................................................................... 34
Magnetic Materials used in Electrical Machines ........................................................... 34
3.1.1
Non-oriented Steel .................................................................................................. 34
3.1.2
Grain-oriented Steel ................................................................................................ 35
3.2
Finite element modeling of Salient Pole Synchronous Machine ................................... 35
3.2.1
Salient Pole Synchronous Motor ............................................................................ 36
3.2.2
Salient pole synchronous generator ........................................................................ 39
3.3
AT (ampere turn) Distribution Scheme .......................................................................... 42
3.3.1
Steps of AT distribution scheme ............................................................................. 42
3.3.2
Open circuit test ...................................................................................................... 43
3.3.3
Magnetostatic simulation in Ansys Maxwell .......................................................... 44
3.3.4
Calculation of ampere turns for different parts of the motor: ................................. 50
3.3.5
Calculation of magnetic flux density from the experiment data ............................. 53
3.4
Comparison of Steel1008, M27 and the new material ................................................... 63
3.5
Conclusion...................................................................................................................... 67
Chapter 4
Comparison of results with new magnetic material and real SPSM ....................... 68
4.1
SPSM as a Motor ........................................................................................................... 68
4.2
Comparison of Experiment and FE at different load conditions with SPSM as a Motor
70
4.2.1
Full Load condition ................................................................................................. 70
vi
4.2.2
75% Full Load condition ........................................................................................ 72
4.2.3
66% Full Load condition ........................................................................................ 74
4.2.4
50% Full Load condition ........................................................................................ 76
4.2.5
33% Full Load condition ........................................................................................ 78
4.2.6
No Load condition .................................................................................................. 80
4.3
Harmonic analysis of the stator current in SPSM as a motor......................................... 86
4.4
SPSM as a generator ...................................................................................................... 89
4.4.1
Generator with Resistive Load................................................................................ 90
4.4.2
Generator with Resistive-Inductive (RL) Load ...................................................... 95
4.4.3
Generator with Resistive-Capacitive (RC) Load: ................................................. 100
Chapter 5
Conclusion ............................................................................................................ 107
5.1
Conclusion.................................................................................................................... 107
5.2
Advantages and Disadvantages of the ampere turn distribution scheme ..................... 107
5.3
Contributions ................................................................................................................ 108
5.4
Future Scope................................................................................................................. 109
References: .................................................................................................................................. 110
Appendix ..................................................................................................................................... 113
vii
List of Figures
Figure 1-1. Classification of magnetic measurement techniques ................................................... 2
Figure 1-2. Different shapes of the sample for ring tester [2] ........................................................ 3
Figure 1-3. Ring test rig with control algorithm [3] © 2011, IEEE ............................................... 4
Figure 1-4. Single Sheet Tester frame [6] © 1974, IEEE .............................................................. 7
Figure 1-5. Single Sheet Tester [6] © 1974, IEEE ........................................................................ 8
Figure 1-6. 2H coil SST [7] © 2009, IEEE .................................................................................... 9
Figure 1-7. 2H SST measurement system [7] © 2009, IEEE ........................................................ 9
Figure 1-8. Double excitation SST [8] © 1999, IEEE ................................................................. 10
Figure 1-9. Open Type SST - DC magnetization [9] © 2010, IEEE ........................................... 11
Figure 1-10. 3D tester (cubic sensing box) [10] © 2010, IEEE................................................... 12
Figure 1-11. 3D tester for SMC [11] © 2003, IEEE .................................................................... 13
Figure 1-12. Epstein FEM [13] © 2005, IEEE ............................................................................ 14
Figure 1-13. SST FEM [13] © 2005, IEEE ................................................................................. 14
Figure 1-14. Geometry of induction motor [14] © 2012, IEEE................................................... 15
Figure 2-1. Electromagnetic Analysis Solution [17] .................................................................... 19
Figure 2-2. FE software process [18] ............................................................................................ 23
Figure 2-3. Ansys Maxwell - process flow [20] ........................................................................... 24
Figure 2-4. Ansys Maxwell and related products [20] ................................................................. 25
Figure 2-5. RMxprt - DC motor [21] ............................................................................................ 26
Figure 2-6. Field calculator [22] ................................................................................................... 27
Figure 2-7. Magnetostatic Solution Process [17].......................................................................... 29
Figure 2-8. Eddy current solution process [17] ............................................................................ 30
Figure 2-9. Transient Solution process [17] ................................................................................. 31
Figure 2-10. Material Properties ................................................................................................... 32
Figure 2-11. M27 Core loss Model (Red curve – actual one and Black curve – inserted
automatically by Maxwell to smoothen the characteristics) ......................................................... 33
Figure 3-1. Salient pole synchronous machine – FE model ......................................................... 36
Figure 3-2. Excitation voltage - winding 1 ................................................................................... 37
Figure 3-3. Excitation voltage - winding 2 ................................................................................... 37
Figure 3-4. Field circuit for motor ................................................................................................ 38
viii
Figure 3-5. Field current ............................................................................................................... 38
Figure 3-6. Load setting ................................................................................................................ 39
Figure 3-7. Constant Speed - Prime mover setting ....................................................................... 40
Figure 3-8. Constant speed of 1800 RPM ..................................................................................... 41
Figure 3-9. Circuit for generator with R Load .............................................................................. 41
Figure 3-10. Steps in AT (ampere turn) distribution scheme ....................................................... 43
Figure 3-11. Optometrics setup..................................................................................................... 45
Figure 3-12. Field winding (Pink) in SPSM ................................................................................. 46
Figure 3-13. Plot of H for 0.5A Field Current .............................................................................. 47
Figure 3-14. Plot of B for 0.5A Field Current .............................................................................. 48
Figure 3-15. Modify attribute tab in magnetostatic simulation .................................................... 49
Figure 3-16. Ampere turn distribution in SPSM........................................................................... 52
Figure 3-17. Ampere turn distribution steps shown in Table 3-8 ................................................. 58
Figure 3-18. BH steel1008 vs New material ................................................................................. 63
Figure 3-19. BH plot of different parts of SPSM based on Table 3-9, 3-11 and 3-12.................. 64
Figure 3-20. Comparison of generated voltage............................................................................. 66
Figure 3-21. Comparison of OCC difference - Steel1008, M27 and new Material from the
experimental OCC ........................................................................................................................ 66
Figure 4-1. SPSM used in the experiments ................................................................................... 68
Figure 4-2. Stator current of SPSM at FL at 0.7A field current ................................................... 71
Figure 4-3. Stator current of SPSM at FL - zoomed in version of Figure 4-2 .............................. 72
Figure 4-4. Stator current of SPSM at 75% FL at 1A field current .............................................. 73
Figure 4-5. Stator current of SPSM at 75% FL - zoomed in version of Figure 4-4 ..................... 74
Figure 4-6. Stator current of SPSM at 66% FL at 1.2A field current .......................................... 75
Figure 4-7. Stator current of SPSM at 66% FL - zoomed in version of Figure 4-6 .................... 76
Figure 4-8. Stator current of SPSM at 50% FL at 1A field current .............................................. 77
Figure 4-9. Stator Current of SPSM at 50% FL - zoomed in version of Figure 4-8..................... 78
Figure 4-10. Stator current of SPSM at 33% FL at 0.7A field current ......................................... 79
Figure 4-11. Stator current of SPSM at 33% FL - Zoomed in version ......................................... 80
Figure 4-12. Stator current of SPSM at NL at 1.2A field current ................................................. 81
Figure 4-13. Stator Current of SPSM at NL - Zoomed in version ................................................ 82
ix
Figure 4-14. Comparison of stator current at 0.7A field current .................................................. 82
Figure 4-15. Comparison of stator current at 1A field current ..................................................... 83
Figure 4-16. Comparison of stator current at 1.2A field current .................................................. 83
Figure 4-17. Comparison of power factor at 0.7A field current ................................................... 84
Figure 4-18. Comparison of power factor at 1A field current ...................................................... 84
Figure 4-19. Comparison of power factor at 1.2A field current ................................................... 85
Figure 4-20. FFT of stator current (a) Experimental SPSM (b) FE simulation of SPSM with
new material (c) FE simulation of SPSM with M27.................................................................... 87
Figure 4-21 – Experimental set up of the generator ..................................................................... 89
Figure 4-22. Generated voltage of SPSM at 50% FL and 0.9A field current for R load.............. 92
Figure 4-23. Zoomed in version of Figure 4-22 ........................................................................... 93
Figure 4-24. Comparison of phase voltage for R load at 0.72A field current .............................. 93
Figure 4-25. Comparison of phase voltage for R load at 0.9A field current ................................ 94
Figure 4-26. Comparison of phase voltage for R load at 1.08A field current .............................. 94
Figure 4-27. Generated voltage of SPSM at 50% FL and 0.9A field current for RL load ........... 97
Figure 4-28. Zoomed in version of Figure 4-27 ........................................................................... 98
Figure 4-29. Comparison of phase voltage for RL load at 0.72A field current ............................ 98
Figure 4-30. Comparison of phase voltage for RL load at 0.9A field current .............................. 99
Figure 4-31. Comparison of phase voltage for RL load at 1.08A field current ............................ 99
Figure 4-32 – Generated voltage of SPSM at 50% FL and 0.9A field current for RC load ....... 102
Figure 4-33 – Zoomed in version of Figure 4-32 ....................................................................... 103
Figure 4-34. Comparison of phase voltage for RC load at 0.72A field current .......................... 103
Figure 4-35. Comparison of phase voltage for RC load at 0.9A field current ............................ 104
Figure 4-36. Comparison of phase voltage for RC load at 1.08A field current .......................... 104
Figure A1 - SPSM wiring diagram ............................................................................................. 113
Figure A2 - SPSM datasheet ....................................................................................................... 114
x
List of Tables
Table 1-1. Comparison of Epstein and SST [16] .......................................................................... 16
Table 2-1. Electrical machine design software packages ............................................................. 22
Table 3-1. Composition of silicon steel [23] ................................................................................ 35
Table 3-2. Open circuit voltage - comparison of different materials with the experimental motor
....................................................................................................................................................... 44
Table 3-3. Field current - FE......................................................................................................... 47
Table 3-4. Magnetic field intensity (AT/m) of Core, Yoke, Pole, Teeth of SPSM ...................... 48
Table 3-5. Length of different parts of the SPSM ........................................................................ 50
Table 3-6. Ampere Turn for Field Current of 1A ......................................................................... 50
Table 3-7. Ampere turns from FE simulation ............................................................................... 56
Table 3-8 . Estimated distribution of ampere turns for the actual machine .................................. 57
Table 3-9. Magnetic field intensity for actual machine ................................................................ 58
Table 3-10. BH for core ................................................................................................................ 59
Table 3-11. BH for Yoke .............................................................................................................. 60
Table 3-12. BH for Teeth .............................................................................................................. 61
Table 3-13. BH for Pole ................................................................................................................ 62
Table 3-14. Comparison of open circuit voltage for different materials ...................................... 65
Table 4-1. Motor experiments....................................................................................................... 69
Table 4-2. Stator current of the motor at FL condition ................................................................. 70
Table 4-3. Power factor at FL condition ....................................................................................... 71
Table 4-4. Stator current of the motor at 75% FL condition ........................................................ 72
Table 4-5. Power factor at 75% FL condition............................................................................... 73
Table 4-6. Stator current of the motor at 66% FL condition ........................................................ 74
Table 4-7. Power factor at 66% FL condition............................................................................... 75
Table 4-8. Stator current of the motor at 50% FL condition ........................................................ 76
Table 4-9. Power factor at 50% FL condition............................................................................... 77
Table 4-10. Stator current of the motor at 33% FL condition ...................................................... 78
Table 4-11. Power factor at 33% FL condition............................................................................. 79
Table 4-12. Stator current of the motor at NL condition .............................................................. 80
Table 4-13. Power factor at NL condition .................................................................................... 81
xi
Table 4-14. Percentage deviation of stator current from the experiment for M27 and new material
....................................................................................................................................................... 86
Table 4-15. Spectrum analysis of the stator current of SPSM ...................................................... 88
Table 4-16. Generator experiments............................................................................................... 90
Table 4-17. Phase voltage at FL as a generator for R load ........................................................... 91
Table 4-18. Phase voltage at 75% FL as a generator for R load ................................................... 91
Table 4-19 - Phase voltage at 66% FL as a generator for R load ................................................. 91
Table 4-20. Phase voltage at 50% FL as a Generator for R load .................................................. 92
Table 4-21. Phase voltage at 25% FL as a generator for R load ................................................... 92
Table 4-22. Percentage deviation of phase voltage from the experiment for M27 and new
material for R load ........................................................................................................................ 95
Table 4-23. Phase voltage at FL as a generator for RL load ......................................................... 96
Table 4-24. Phase voltage at 75% FL as a generator for RL load ................................................ 96
Table 4-25. Phase voltage at 66% FL as a generator for RL load ................................................ 96
Table 4-26. Phase voltage at 50% FL as a generator for RL load ................................................ 96
Table 4-27. Phase voltage at 25% FL as a generator for RL load ................................................ 97
Table 4-28. Percentage deviation of phase voltage from the experiment for M27 and new
material for RL load .................................................................................................................... 100
Table 4-29. Phase voltage at FL as a generator for RC load ...................................................... 101
Table 4-30. Phase voltage at 75% FL as a generator for RC load .............................................. 101
Table 4-31. Phase voltage at 66% FL as a generator for RC load .............................................. 101
Table 4-32. Phase voltage at 50% FL as a generator for RC load .............................................. 101
Table 4-33. Phase voltage at 25% FL as a generator for RC load .............................................. 102
Table 4-34. Percentage deviation of phase voltage from the experiment for M27 and new
material for RC load.................................................................................................................... 105
xii
List of Abbreviations
AC – Alternating Current
AT – Ampere Turn
DC – Direct Current
FE – Finite Element
FEA – Finite Element Analysis
FEM – Finite Element Model
FFT – Fast Fourier Transform
FL – Full Load
IEC – International Electrotechnical Commission
NL – No Load
OCC – Open Circuit Characteristics
PF – Power Factor
RD – Reverse Direction
SMC – Soft Magnetic Composite
SPSM – Salient Pole Synchronous Machine
SST – Single Sheet Tester
TD – Transverse Direction
xiii
List of symbols
– Area of the core (m2)
– Area of the pole (m2)
– Area of the teeth (m2)
– Area of the yoke (m2)
– Ampere turn of the core (AT)
– Ampere turn for the experiment (AT)
– Ampere turn for FE simulation (AT)
– Ampere turn of the air gap (AT)
– Ampere turn of the iron (AT)
– Ampere turn of the pole (AT)
– Ampere turn of the teeth (AT)
– Ampere turn of the yoke (AT)
B – Magnetic flux density (T)
– Magnetic flux density of the air gap (T)
- Magnetic flux density of the core (T)
- Magnetic flux density of the yoke (T)
- Magnetic flux density of the pole (T)
- Magnetic flux density of the teeth (T)
– Breadth of the pole (m)
C – Capacitance (F)
xiv
– Width of the core (m)
– Width of the yoke (m)
- Phase voltage (V)
f – Frequency (Hz)
H – Magnetic field intensity (AT/m)
IF - field current (A)
- Field form factor
- Gap contraction factor
– Winding factor
L – Inductance (H)
– Length of the core (m)
– Length of the pole (m)
– Length of the teeth (m)
– Length of the yoke (m)
– Length of the air gap (m)
N – Number of turns
NF – Total number of turns in the field winding
– Pole arc (m)
R – Resistance (Ω)
– Width of the teeth (m)
xv
- Flux per phase (wb)
– Pole pitch (m)
– Permeability of free space (m kg s-2 A-2)
xvi
Acknowledgements
I would like to sincerely thank my supervisor Dr.Nandi for spending his valuable time in
guiding me through this research work. I would also like to acknowledge him for the detailed
supervision, advice, ideas and words of encouragement which helped me complete the thesis.
I would like to thank the other member of my supervisory committee Dr.Nikitas Dimopolous for
agreeing to be in my supervisory committee.
I would like to thank Mr.Rob Fichtner and Mr.Kevin Jones for helping me in the setup of the
simulations and experiments.
I would like to thank Ilamparithi, Nagendrappa, Premkumar, Nethra and Komal for their
continuous support and words of encouragement throughout my degree. I would also like to
thank my friends Karthik, Raghavendran, Yashu, Jainish and Thejasvi for keeping me motivated
through these years.
Last but not the least I would like to thank my family members without whom this work would
have never been possible.
xvii
Dedication
Dedicated to my Amma, Appa and Jayashri
xviii
Chapter 1
Introduction
to
magnetic
measurement
techniques in rotating machines
1.1 Introduction to modeling of electrical machines
Modeling of electrical machines is important for the following reasons:
1. Design and performance analysis of machines
2. Fault diagnosis and condition monitoring of the machines
3. Analyzing the characteristics of the electrical machines
4. Thermal and stress analysis under extreme conditions
There are a plethora of modeling techniques of electrical machines available for researchers such
as finite element modeling and mathematical modeling. Of these, mathematical modeling is used
for the parametric estimation of the electrical machines and the detailed mathematical modeling
of motors is shown in [1]. Finite element (FE) method of electromagnetic analysis involves
utilizing either own FE code or using commercial Finite software packages in the market. While
modeling using FE method in these commercial software packages, one of the important
parameters while defining the machine is the material used in the motor. The characteristics of
the conductors and the core have to be specified in the motor model. Therefore knowledge of the
magnetic characteristics of the material is highly important and usually the manufacturers can
provide the details of the material used in the motor. Sometimes it is difficult to know the
magnetic characteristics of the material since their characteristics might change due to aging,
thermal and mechanical stresses on the machines. Therefore the determination of the magnetic
characteristics is important not only when the motor is new but also periodically as long as the
machine remains in service. This is to evaluate the performance of the motor continuously and
check for faults which might develop in the machine while in operation. Some of the commonly
used FE software packages in the modeling of electrical machines are Ansys, Magnet and
Modelica. Detailed descriptions of these software packages and their characteristics are
presented in chapter 2.
1
1.2 Introduction to measurement techniques of magnetic
characteristics of materials in Electrical machines
There are three main techniques in the determination of the magnetic characteristics of the
material. They are Ring test, Epstein test and Single sheet test. Of these, Epstein test is widely
used, followed by Single sheet test. Descriptions of these techniques are given below:
A classification of the current magnetic measurement techniques is shown below in Figure 1-1.
Figure 1-1. Classification of magnetic measurement techniques
2
1.2.1 Ring Test
Ring test is the most fundamental method of testing the magnetic properties of a material. Here
annealing has to be done to reduce the effect of stresses in the material being used. The
measurement of the core losses and hysteresis losses are done using the wattmeter method. The
shape of the sample can be of different forms as shown in Figure 1-2 [2].
Figure 1-2. Different shapes of the sample for ring tester [2]
Once the sample is ready, the primary and secondary windings are wound around the sample to
measure the core loss similar to a transformer experiment. This is a primitive and destructive
method of testing and not widely used now.
Modifications were made to this technique by introducing a test bed incorporated with a new
control algorithm to calculate all the measurement systems as shown in [3].This was followed by
FE simulation of the stator yoke to verify the iron loss of the material. The test rig is shown in
Figure 1-3.
3
Figure 1-3. Ring test rig with control algorithm [3] © 2011, IEEE
1.2.2 Epstein Test
A 25cm Epstein frame with double lapped joints has been the standardized procedure for
characterization of magnetic characteristics of soft magnetic materials in the industries since
1936 [4]. Epstein tester follows the standard in IEC 402-2. This procedure has been tested by a
lot of researchers and the results are highly reproducible. Hence the industry and researchers
have widely preferred to use the Epstein tester for the determination of the magnetic properties
of a given magnetic material. The setup of Epstein tester for magnetic measurement is as follows.
Epstein test frame is designed using four strips of the magnetic material (or multiples of four)
superposed at corners by double lapped joints. Each side of the square is provided with a
secondary coil and external to it, a primary winding put together in a rigid rectangular frame. A
total of 700 turns are used for the primary and secondary windings for DC and power frequency
measurements (IEC 60404-2) and 200 turns for medium frequency testing (IEC60404-10). The
sample to be tested must be 30mm wide and 280 – 305mm in length. The mean magnetic path
4
length is assumed to be 0.94m and this assumption has been tested in different methods in [5].
The Epstein frame can operate up to levels of 30KA/m and 1.5T with an accuracy of 1.5%. The
power losses are measured by means of wattmeter method and during the experiment
measurement, the Epstein frame behaves as an unloaded transformer. The magnetizing field
intensity for individual test points in this procedure is calculated using the formula.
where
– Magnetic field intensity
– Number of magnetizing winding turns
– Magnetizing current (Peak amperes)
– Mean magnetic path length (0.94m)
With
= 0.94m and 25cm frame, the equation reduces to
The magnetic field is determined using the formula
where
– Measured Voltage
– Frequency
– Area of the sample
Some of the advantages of the Epstein frame technique are:
1. Epstein tester is widely used and rigorously tested technique. Therefore reproducibility of
results is easy.
2. The test sample can be placed in the test rig and can be removed after testing. Therefore
easy replacement of the sample is possible. Furthermore since there is direct relationship
between the current, H and Area, precalculated tables can be used for routine testing.
5
3. The test sample lies loosely in the test rig. Therefore no pressure, bending or strain is
subjected on the test sample/strips.
Some of the disadvantages of the Epstein frame technique are:
1. This is a destructive method of testing and there is a requirement of a large amount of
samples for testing.
2. Epstein works only till B = 1.5T for non-oriented steel and 1.8T for oriented steel
measurements. At high flux densities, digital control is necessary and the reproducibility
and accuracy reduces.
3. The preparation of the specimen is time consuming and tedious.
1.2.3 Single Sheet Test (SST)
1.2.3.1
Single Excitation
SST is an alternate method for Epstein technique and tries to avoid some of its difficulties. The
principle of SST is similar to an open circuit test in a transformer as shown in Figure 1-4. The
specimen to be tested is placed between the yoke which employs a measuring coil to determine
the B and H and a primary winding to apply the magnetizing field. In SST, the H and B values
are acquired directly using a flux meter [7] and does not require calculations from the
magnetizing current and mean magnetic path length like the Epstein technique. To achieve that,
the flux must be uniform over the region being measured and such conditions can be achieved by
using yokes as shown in [6]. Figure 1-5 shows the measuring instrument for the SST. It can be
seen that the value of flux density can be calculated directly using the voltage divider and digital
voltmeter. The core loss is measured using the equation shown below
where
– Magnetic field intensity
6
– Magnetic flux density
– Period of the fundamental wave
The voltage induced in the H coil is amplified and the voltage induced in the B coil is integrated
and amplified. These two voltages are multiplied and averaged over a single period.
Current international standard for SST are 50cm square sample, Single magnetizing coils and
two yokes
Advantages:
1. It has similar measurement quantities like the Epstein frame.
2. It is easier to prepare the specimen.
3. It requires lower specimen mass and is easier to install compared to Epstein frame.
4. Easy to remove the samples and replace it with a new specimen.
Disadvantages:
1. It is an invasive method of testing i.e. it requires samples of a material in a specific shape.
2. It does not have good reproducibility.
Figure 1-4. Single Sheet Tester frame [6] © 1974, IEEE
7
Figure 1-5. Single Sheet Tester [6] © 1974, IEEE
One of the important aspects in the determination of magnetic characteristics is to determine the
BH characteristics of the material at high flux densities i.e. above 1.5T. This aspect is one of the
disadvantages with both Epstein and SST and has been tackled by researchers by introducing
novel models of the SST.
1.2.3.2
Double Excitation:
In reference [7], a novel method of double excitation type SST in determining the magnetic
properties is shown. Here, a novel 2H coil method is proposed for the H coils to be used in the
SST. Figure 1-6 shows the 2H coil pair used in this method for the SST. The complete
measurement system is shown in Figure 1-7. The two H coils help in increasing the accuracy
while measuring the magnetic properties up to 2.1 T and H of 58000 A/m.
In reference [8], a double excitation type SST was introduced to help determine the magnetic
properties at higher flux densities. The SST developed for this scheme is shown in Figure 1-8.
Two magnetizing windings have been introduced – one for rolling direction (RD) and one for
transverse direction (TD) as shown in Figure 1-8. These two windings helps in satisfying the
8
rotating flux condition exhibited in rotating machines. The way in which the TD winding is
placed inside the RD helps in increasing the maximum flux density. In this type of excitation,
closed path magnetic circuit was realized successfully to measure high flux densities. The results
were in good agreement with the results from a normal SST at low flux densities proving the
effectiveness of the double excitation type SST.
Figure 1-6. 2H coil SST[7] © 2009, IEEE
Figure 1-7. 2H SST measurement system [7] © 2009, IEEE
9
Figure 1-8. Double excitation SST[8] © 1999, IEEE
1.2.3.3
Open Type SST:
All the above SST and Epstein techniques are mainly used for AC excitation and determination
of magnetic properties under AC excitation. Reference [9] shows the technique to determine
magnetic properties under DC excitation using SST. This is particularly useful for determining
iron losses for reactors in an inverter which works with DC excitation. An open type SST is
designed with a help of Helmholtz coil as shown in Figure 1-9. The H is found by using a Hall
probe since it is difficult to measure Hdc using normal H coil and to determine the change in B,
the output of B coil is integrated during change of current from zero to a specified value in the
Helmholtz coil.
10
Figure 1-9. Open Type SST - DC magnetization [9] © 2010, IEEE
1.2.4 Other Techniques
1.2.4.1
3D Tester
Determination of magnetic characteristics is important for machine modeling and since the
electrical machines experience 3D flux, the measurement technique must incorporate the effect of
3D flux in its calculations. Therefore few techniques were developed including these effects.
Reference [10] shows a technique of measuring the magnetic properties of grain oriented steel
using a 3D tester model. The structure of the tester is shown in Figure 1-10. Using this technique,
BH loci, core losses were calculated and validated with the experimental results. The
disadvantage of this scheme was the difficulty in the production of strong fields while maintaining the
field pattern.
11
Figure 1-10. 3D tester (cubic sensing box) [10] © 2010, IEEE
Reference [11] shows another 3D tester model for measuring the magnetic properties of the soft
magnetic composite (SMC) material. This method also estimates the BH loci, power loss and
core losses in the material. The structure of this tester is shown in Figure 1-11. Finite element
model of the tester and the whole system was developed and studied and was followed by the
implementation in an experimental test system.
All these techniques clearly shows that to identify a magnetic characteristics of a material, a
separate specimen of the material in certain shapes is required which is followed by testing of
that material in different conditions.
1.2.4.2
FE model
A two dimensional approach of finite element proposed in [12] by Enokizono was analyzed to
determine the magnetic characteristics of a material. This approach attempted to determine the 2D
magnetic properties at high flux density as this is important for a lot of applications of which
electrical machine modeling and analysis is one. An extrapolation technique is used to determine
the magnetic properties at high flux density above the saturation level of 2T. Bezier interpolation
technique is used to determine the necessary co-efficient for Newton-Raphson iteration. This
12
showed the importance of Bezier interpolation technique in the identification of 2D magnetic
properties.
Figure 1-11. 3D tester for SMC[11] © 2003, IEEE
A three dimensional approach for Finite Element modeling has been proposed in [13]. A 3D
FEM was modeled for Epstein and SST and their results were compared. The 3D FEM modeling
strategy for Epstein and SST are shown in Figure 1-12 and Figure 1-13 respectively. lFE in
Figure 1-12 represents the length of the laminated magnetic core. It was found that Epstein
showed more error compared to SST during FEM modeling.
13
Figure 1-12. Epstein FEM [13] © 2005, IEEE
Figure 1-13. SST FEM [13] © 2005, IEEE
14
1.2.4.3
Nondestructive Testing
Reference [14] describes a non-destructive method for the detection of BH characteristics of a
material of a motor. It uses local and global magnetic measurements and objective functions to
determine the B-H curve of the material through optimization techniques. Global measurements
measure the excitation current and voltage which is used to determined the coupled magnetic
flux. Local measurements measure the flux in a tooth by adding a search coil. Then using
numerical inverse method and iteratively minimizing the quadratic difference between simulated
and measured peak magnetic flux, the BH curve is obtained. The evaluation of these quadratic
functions needs a lot of computations to minimize the error between simulated and measured
quantities. Also a few more calculations have to be done during the computation of the magnetic
flux of the material. Overall this method is computationally and memory requirement wise
intensive. Besides, the machine has to be disassembled in order to put in search coils around
stator teeth for measurement purposes. Also a hole has to be drilled to add these search coils to
measure the flux. The geometry of the studied asynchronous motor is shown in Figure 1-14.
Figure 1-14. Geometry of induction motor [14] © 2012, IEEE
15
Reference [15] uses discrete evolutionary (DE) optimization technique to find the B-H
characteristics of the material in a synchronous generator. In this method, permeability, current
density, and bend adjustment co-efficient are optimized using DE optimization technique to
reduce the error in the estimated no load voltages. While this method was very accurate in
predicting the open circuit characteristics of the generator, integrating such optimization
procedures with commercially available software would require considerable effort.
1.2.5 Comparison of Epstein and SST techniques
S.No
Epstein Tester
SST (82)
Acceptance
Good
Fair
Reproducibility
Good
Poor
Simplicity
Good
Poor
Applicability
Poor
Good
Calibration facility
Poor
Poor
Technique
Invasive
Invasive
Table 1-1. Comparison of Epstein and SST [16]
1.3 Motivation of the present research work
From the above techniques for magnetic measurements, it can be clearly seen that the existing
techniques have limitations such as the requirement of specimen material, invasive technique and
destruction of the tested specimens. Therefore a non-invasive method without the requirement of
an additional specimen material needs to be developed for machines already in operation.
In this research work, an attempt has been made to develop a technique which is non-invasive and
involves simple calculations to determine the BH (Magnetic flux density-Magnetic field intensity)
characteristics of the material used in salient pole synchronous machine (SPSM). The stator of the
real SPSM used for testing is made of M27 and the rotor is made of steel whose BH characteristic
is unknown. FE modeling has been done using Ansys Maxwell for the SPSM. Experimental open
circuit test results were compared with those obtained from the FE simulations and a novel
ampere turn distribution technique was developed using a known magnetic material with
characteristics expected to be similar to the actual one in order to match the BH characteristics of
16
the actual material used in the machine. Following this, simulations and experiments were
performed to compare the simulated characteristics of the electrical machine with the newly
determined material to the experimental motor and generator characteristics.
To the best knowledge of the author, ampere turn distribution technique is a completely new
method to determine the BH characteristics of a material used in SPSM.
1.4 Thesis outline
The structure of the thesis is as follows:
In chapter 1, a discussion on the existing techniques to measure the magnetic properties such as
Epstein tester and single sheet tester have been presented. This was followed by a comparison of
the existing techniques and their shortcomings. Next, a survey on the latest techniques to
determine the magnetic properties has been provided. Finally, the motivation of the thesis has
been presented to stress the need for a non-invasive technique for the determination of the
magnetic properties of the material in rotating machines.
In chapter 2, discussions have been provided on the FE software package, Ansys Maxwell. The
advantages, disadvantages and the tools available in Ansys Maxwell have been presented in a
detailed manner. The tools available in creating models for magnetostatic measurements have
been provided.
In chapter 3, theoretical calculation in determination of the magnetic characteristics of the
material has been provided followed by the modeling of the SPSM machine using Ansys
Maxwell. Details have been provided on the creation of SPSM models using Ansys Maxwell for
different conditions such as the motor and generator and for different loads. Further the ampere
turn distribution technique to determine the magnetic characteristics has been described in detail.
In chapter 4, simulations have been performed under various conditions for SPSM to test the
newly determined material and to compare it with the experimental results. Open circuit test,
motor and generator tests were performed at different load conditions and different field currents
to give a comprehensive analysis on the accuracy of the newly derived material characteristics
using the ampere turn distribution technique.
17
In chapter 5, the advantages and shortcomings of this ampere turn distribution scheme have been
provided. Finally, the contributions of the research, future scope and conclusion have been
discussed.
18
Chapter 2
Finite Element Modeling
2.1 Electromagnetic analysis
Solving electromagnetic problems has always been a difficult task because of the complications
associated with varying and complex geometric shapes, materials along with complex
mathematical operations involved in their solutions. Some of the techniques available for solving
electromagnetic problems are shown in Figure 2-1.
Figure 2-1. Electromagnetic Analysis Solution [17]
Of all the techniques available for solving the electromagnetic problems, finite element method
has emerged as one of the robust methods for the analysis and finding the best possible solution.
19
2.2 Finite Element Analysis (FEA):
FEA is a numerical method for solving multiphysics problems. It is usually employed for
problems with complicated geometries, loading and material properties. This method is usually
used where an analytical solution may be difficult to handle and other modeling methods do not
give accurate results. The model to be solved is first defined geometrically into smaller bodies
interconnected by simple boundary lines or surfaces. These smaller bodies are solved using
simpler equations and then followed by a calculus of variations method to minimize an
associated error function.
Some of the advantages of FEA are:

Complex geometry can be included without difficulty and solved.

Different materials can be used with different parts of the geometry.

Local effects can be captured as the whole model is subdivided into simpler bodies

Total solution can be represented at the end for this complex geometry.
Some of the disadvantages of FEA are:

Only an approximate solution is provided

FE method provides element dependent solution i.e. for irregular shaped elements,
accuracy of the solution is less.

Using high quality numerical methods is restricted due to large number of meshes to be
solved resulting in a very long solution time.
Applications of Finite Element method include:

Mechanical/Aerospace/Civil/Automobile

Structural Analysis

Electromagnetic problems

Thermal analysis/Fluid dynamics

Geomechanics /Biomechanics
20
2.3 FE in Electrical Machines
FEA is widely used for electromagnetic problems. It is widely used in the modeling of electrical
machines as it helps in understanding the characteristics of the machine under different
conditions without the need for an actual motor with reasonable accuracy. Furthermore from the
advantages shown above for FEA, it can be clearly seen that FEA is a very useful scheme for
electrical machine modeling as the machines exhibit complexities in their geometry and the
usage of different materials in their construction. It is therefore clear that FEA is an important
tool for designers of electrical machines for achieving low cost, high efficiency, reliability and
minimum weight by optimizing the performance of the machine through proper design. Since FE
simulation gives realistic results, different working conditions can be tested such as running the
electrical machines as a:
1. Motor
2. Generator
3. OC/Short Circuit test
All these different characteristics can be studied under different loading conditions and different
field currents. Also, with new types of electrical machines being developed, it becomes highly
important to analyze these machines extensively to study their characteristics and functioning
[18]. Since FE method is computationally intensive, the ability of the computers to run multiple
processes followed by high CPU power becomes a necessity. Current availability of inexpensive
multiprocessor capability, high CPU power and memory makes FE method a feasible method for
the study of electrical machines.
In addition, different fault conditions can be incorporated easily to study the effects of the faults
on the input and output characteristics of the machine. This has been suitably proved in [19].
Hence FE modeling plays an important role in the study of electrical machines.
21
2.4 Commercial FE packages available for Electrical
Machines:
Some of the commonly used software packages in electrical machine modeling are Ansys
Maxwell, Comsol, Modelica, Flux and Speed. The field of application of these software
packages is given in Table 2-1.
S.No
Software
License
Field of application
1
Ansys
Proprietary
Ansys provides solution for different areas such as
Electronics, Electromagnetics, Multiphysics, Fluids
and structures
2
Comsol
Proprietary
Comsol is widely used for MEMS, CFD and structural
analysis
3
MagNet
Proprietary
MagNet is a product of Infolytica corporation which is
dedicated for solving Electrical machine problems.
4
Flux
Proprietary
Flux is designed for electromagnetic and thermal
analysis. It is used for electromagnetic devices such as
electrical machines, Transformers, HV devices, cables
and induction devices
5
Modelica
Non Proprietary
Modelica is used for solving electromagnetic problems
by differential, algebraic and discrete equations
6
MEGA
Proprietary
MEGA was developed for 2D and 3D finite element
analysis of electromagnetic fields. It was designed by
a group in the University of Bath
7
SPEED
Proprietary
It is a dedicated software for electromagnetic analysis
of Electrical Motors
Table 2-1. Electrical machine design software packages
There are several other in house systems and open source software packages developed for
electrical machines but the table above gives the widely used and popular software packages in
the field of electrical machines.
All of the Finite element software packages follow the general pattern [18]:
22
1. Preprocessing (Model the required geometry, assign material, boundary conditions, loads
and constraints)
2. FEA solver (This is the work of the software package which assembles and solves the
differential equations)
3. Postprocessing (Sort and display the results)
These steps are shown in Figure 2-2
Figure 2-2. FE software process [18]
All the work in this thesis has been done using different products of Ansys software package
such as Maxwell and RMxprt. The details of this software and its capabilities are discussed in
this chapter. Some of the reasons for choosing Ansys software package are the following
1. Ability to perform magnetostatic, electrostatic and transient simulations
2. Ability to provide inbuilt electrical machine modeling packages like RMxprt
3. Ability to scale the problem to different ranges based on the needs.
2.5 Ansys:
Ansys Maxwell is an electromagnetic field simulation software used for 2D and 3D
electromagnetic devices such as motors and transformers. It uses Finite element method to solve
static, frequency domain and time varying electromagnetic and electric fields. This plays a major
role in using Ansys for electrical machine design and analysis.
23
The process flow of the modeling in Ansys Maxwell is shown in Figure 2-3 [20].
Some of the advantages of Ansys Maxwell are
1. Automatic adaptive meshing
2. Dynamic link with Simplorer and Maxwell circuit editor
3. Transient in motion
4. Permanent magnet temperature dependency
However some of the disadvantages are:
1. It takes a long time to obtain a steady state solution. It takes around 13 hours with an intel
i7 core @3.40GHz, Windows 7 OS and 16GB RAM for 2s simulation for a 3 phase, 4
pole, 60Hz, 2KW SPSM.
Figure 2-3. Ansys Maxwell - process flow [20]
24
Figure 2-4. Ansys Maxwell and related products [20]
Figure 2-4 shows the Ansys Maxwell and associated products available to the users for modeling
of electromagnetic devices and machines. Some of the products can be interlinked as shown in
Figure 2-4. For example, a model of electrical machine can be drawn in Ansys Maxwell and can
be linked with Ansys PExprt for control of the machine since PExprt provides the option of
power electronics such as bridges and converters. It can be linked to Simplorer to include a field
circuit for powering the field windings/stator windings of the electrical machine. In this thesis,
Maxwell circuit editor has been used for powering the field windings and stator windings of the
SPSM. The following sections will discuss the important features in Ansys Maxwell which are
useful in electrical machine modeling
2.5.1 Ansys RMxprt
Ansys RMxprt is a template based design tool for Electrical machines in Ansys Maxwell domain.
It has templates for induction motor (single and three phase), synchronous motor (permanent
magnet, salient and round rotor), DC motors (brushless and permanent magnet) and switched
25
reluctance motors. In this template, the outer diameter, inner diameter of the stator, rotor, length,
height of yoke, teeth, number of slots, winding type, number of conductors and type of the
material used have to be filled. Once these data are inserted into the model, they have to be
converted to Maxwell 2D design and run as a Finite Element model. This is a very useful tool
since it saves a lot of time in modeling or drawing the complete motor step by step. Figure 2-5
shows RMxprt modeling of PMDC motor.
RMxprt is particularly useful for designers of electrical machines since it gives the ability to
optimize the machine to identify the best design. RMxprt can be used by clicking on the Project
tab  Insert RMxprt design and by selecting the appropriate machine model. Once a particular
electrical machine is selected from the RMxprt template, the tool gives the general stator and
rotor models. Here suitable details of its size, material and other parameters such as slots and
teeth are filled and tested for its performance. Besides, there is also parametric and optimization
capability built with the tool which automatically varies parameters within the template such as
the diameter of the rotor or the length of the stator [21]. Using this tool, the designers can view
the performance curves and choose the best design. This shows the capabilities of Ansys RMxprt
in the modeling of electrical machines.
Figure 2-5. RMxprt - DC motor [21]
26
2.5.2 Field Calculator:
Field calculator is another feature available in Ansys Maxwell which enables the users to build
and postprocess the solutions obtained from the FE simulation. It has various operations attached
to it such as vector operations, calculus operations, and algebraic operations. It can be applied
over specific geometric shapes to perform field calculations, integrations and for exporting the
determined results. Once the magnetostatic simulation is over, field calculator can be accessed
from the results tab of the project. Figure 2-6 shows the Field calculator tool available in Ansys
Maxwell.
Field Calculator is particularly useful while performing magnetostatic simulations. The three
main purposes of field calculator are as follows:
1. Plot field quantities (Magnetic flux density - B, Magnetic field intensity - H, Current density
- J) over different geometric entities in the Finite Element model
2. Perform integration (Line, surface, volume) over the geometric entities.
3. Export the field result over a specific location or a point.
Figure 2-6. Field calculator [22]
27
Field Calculator is useful for finding the maximum and minimum value as well as the position of
magnetic field intensity, magnetic flux density in a given region. The steps to find the maximum
value and position are shown below.
To get a maximum value of Magnetic flux density (B) in a given volume:
Input > Quantity >B
Vector > Mag
Input > Geometry > Volume (Volume of interest)
Scalar > Max> Value
Output > Eval
To get the position of maximum value of Magnetic flux density (B) in a given volume:
Input > Quantity >B
Vector > Mag
Input > Geometry > Volume (Volume of interest)
Scalar > Max> Position
Output > Eval
The same procedure can be used to find the minimum value and position of B, H and J using
field calculator. There is no direct method available in Ansys Maxwell to determine the average
of B or H in a given region.
2.5.3 Solvers
There are several solvers available in Ansys Maxwell. They are as follows:
1. Magnetostatic
2. Eddy Current
3. Transient
These solvers can be accessed by clicking on tab Maxwell 2d  Solution type. This gives the
three solver types and any one of them can be chosen according to the requirement.
28
2.5.3.1
Magnetostatic Solvers
To perform magnetostatic analysis, magnetostatic solvers have to be used. They are usually used
in inductors, motors, solenoids, actuators and many others and are used for objects that are
stationary. The quantities which are computed through Magnetostatic solvers are magnetic field
intensity (H), magnetic flux density (B) and current density (J). Figure 2-7 shows the steps
involved in magnetostatic solution processes.
Figure 2-7. Magnetostatic Solution Process [17]
2.5.3.2
Eddy Current Solver
To perform magnetostatic analysis, eddy current solvers have to be used. They are usually used
in inductors, motors, solenoids, stray field calculations and many others and are used for objects
that are stationary. The quantities which are computed through eddy current solvers are magnetic
field and magnetic scalar potential. The eddy current solvers are used for steady state, AC
29
magnetic fields at a given frequency. Figure 2-8 shows the steps involved in eddy current
solution processes.
Figure 2-8. Eddy current solution process [17]
2.5.3.3
Transient Solver
To perform transient analysis, transient solvers have to be used. They are usually used in
inductors, motors, solenoids, permanent magnets and many others and are used for objects that
are moving. Figure 2-9 shows the steps involved in transient solution process.
30
Figure 2-9. Transient Solution process [17]
2.5.4 Material Properties
Ansys Maxwell has options for introducing the effect of core loss into the material
characteristics using features available in the material properties tab. Figure 2-10 shows the
options available in Ansys Maxwell for introducing different material characteristics. A specific
BH curve of a material can be added by using the relative permeability tab and by importing the
appropriate BH curve of the material. This feature is extensively used in this thesis to introduce
different BH curves of material and testing the characteristics of the SPSM. Following this, there
is also an option for introducing core loss model into the material. This can be achieved by
adding a type of core loss model. They are of three types – electrical steel, power ferrite or
hysteresis model. Electrical steel core loss model for M27 material is shown in Figure 2-11.
31
Other options available in Ansys Maxwell in the material properties are Bulk conductivity,
Thermal expansion, Young’s Modulus, specific heat and many more. These properties can be
utilized based on the need and the accuracy required for the FE model and the application.
Figure 2-10. Material Properties
32
Figure 2-11. M27 Core loss Model (Red curve – actual one and Black curve – inserted automatically by
Maxwell to smoothen the characteristics)
2.6 Conclusion
This chapter has discussed in detail the need for FE modeling of Electrical machines. It has also
provided comprehensive detail on the Ansys Maxwell software discussing mainly on the features
such as RMxprt, solvers and core loss modeling necessary for the modeling of electrical
machines. Other minor features involved in modeling the SPSM will be discussed in Chapter 3.
33
Chapter 3
Ampere Turn Distribution Scheme
The first part of the chapter deals with the magnetic materials commonly used in salient pole
synchronous machine (SPSM). Following this, the modeling of SPSM as a motor and a generator
using Ansys Maxwell has been discussed. Subsequently the novel scheme developed to
determine the magnetic material used in SPSM has been provided. Furthermore comparison of
the open circuit characteristics has been made with different magnetic materials and the
experimental motor. Thus a complete overview of modeling of electrical machines using Ansys
Maxwell and the ampere turn distribution scheme for determining the magnetic material in
SPSM is provided in this chapter.
3.1 Magnetic Materials used in Electrical Machines
Silicon steel is the commonly used magnetic material for the electrical machines. It is widely
used in transformers, inductors and electrical machines. One of the drawbacks of using steel is
that with aging, the losses increase. The addition of silicon to the steel increases the electrical
resistivity thereby reduces the eddy current losses and also improves the material stability and
age. Silicon steel offers high saturation flux density, good permeability at high flux density and
moderate losses compared to only steel.
Silicon steel contains iron and 0.3 – 4.5% silicon. The percentage of silicon varies with different
grades of silicon steel. Usually low content of silicon is used for electrical machines and high
content of silicon (4-5%) is used for transformers. This silicon steel is graded based on core
losses and are classified into two main categories. They are
1. Non-oriented steel
2. Grain-oriented steel
3.1.1 Non-oriented Steel
Non oriented steel produces the same magnetic domains irrespective of the direction of
magnetization in the plane of the material [23]. The name non oriented distinguishes it from
oriented steel to show that the magnetic properties are the same in all directions.
34
3.1.2 Grain-oriented Steel
Grain oriented steel produces magnetic domains which depends on the direction of rolling [23].
The process of rolling and annealing used during the production of steel can be used to create
steel with superior magnetic properties in one direction and inferior properties in another.
Silicon steel is split into different grades based on the core losses associated with it. The core
losses will vary according to the content of Silicon in the Silicon steel. With increase in silicon,
core loss decreases but it also lowers the induction permeability of the material.
In general silicon steel consists of iron mixed with silicon (Si), carbon (C), manganese (Mn),
phosphorous (P) and sulphur(S). The composition of different types of silicon steel is shown in
Table 3-1.
Composition, %
Description of Material
C
Mn
P
S
Si
Low Silicon Steel
0.003
0.5
0.03
0.001
1.6
Medium Silicon Steel
0.003
0.15
0.01
0.001
2.0
High Silicon Steel
0.003
0.15
0.01
0.001
2.7
Grain Oriented Silicon Steel
0.003
0.07
0.01
0.001
3.1
Table 3-1. Composition of silicon steel [23]
The experimental SPSM used in the testing and experiments as a motor and generator contains
non-oriented steel in its stator. The stator of the SPSM is made up of M27 grade steel and the
material of the rotor is unknown. M27 contains 3% silicon and remaining is mainly iron, apart
from trace quantities of C, Mn, S and P. M27 belong to the group of non-oriented steel. Since the
rotor material in SPSM is unknown, the novel scheme discussed in section 3.3 provides a
suitable solution to determine the BH characteristics of the material in the stator and rotor of the
SPSM.
3.2 Finite element modeling of Salient Pole Synchronous
Machine
As discussed in Chapter 2 on the capabilities of Ansys Maxwell, a salient pole synchronous
machine (SPSM) model was drawn in Maxwell as shown in Figure 3-1. The model was drawn
35
according to the specifications given by the manufacturer. The name plate details, dimensions of
the machine, wiring and connection diagram of the SPSM are provided in the appendix of this
thesis. FE model of SPSM shown in Figure 3-1 can be used for the different purposes such as
1. Motor
2. Generator
3. Short/Open circuit test
These different functions can be achieved by incorporating suitable changes in the excitation and
motion setup of the model. The modifications required to achieve these different conditions will
be discussed in detail in this chapter.
Figure 3-1. Salient pole synchronous machine – FE model
3.2.1 Salient Pole Synchronous Motor
The model shown in Figure 3-1 is used for running the SPSM as a motor. In a motor, supply has
to be given to the stator windings. Therefore in the excitation setup of the FE model, three phase
ac supply of 120V RMS was provided directly to the windings. Figure 3-2 and Figure 3-3 show
the settings given in Ansys Maxwell for the stator windings of the motor. Three phase AC supply
is provided by supplying the voltage directly in the voltage tab with a phase shift of 120 degrees.
The resistance and the inductance for the stator windings are given from the motor datasheet.
36
Type of the winding in the SPSM is stranded conductors and it can be selected in the type tab. In
addition, the stator resistances and inductance can be included in the windings to create a
realistic model of the stator windings. These values were given based on the manufacturer’s data.
The current to the field windings can be provided using the circuit shown in Figure 3-4. The
resistance and the inductance shown in Figure 3-4 are the field circuit parameters that need to be
entered separately. The gradual buildup of field current is shown in Figure 3-5.
Figure 3-2. Excitation voltage - winding 1
Figure 3-3. Excitation voltage - winding 2
37
Figure 3-4. Field circuit for motor
Field Current vs Time
1.4
1.2
Current (A)
1
0.8
0.6
0.4
0.2
0
0
0.5
1
Time (s)
1.5
2
Figure 3-5. Field current
38
Figure 3-6. Load setting
To vary the load to different conditions, the motion set up tab is modified. This is shown in
Figure 3-6. Different loads can be set up by modifying the load torque to different values. The
full load is 10.6Nm (the negative sign in Figure 3-6 indicates that the externally applied load
torque) and therefore different loading conditions can be given directly based on the percentage
of this full load torque. The comparison of the simulation and the experimental results of SPSM
with the newly determined material and real motor for different field currents and different
loading conditions are shown in detail in Chapter 4.
3.2.2 Salient pole synchronous generator
The model shown in Figure 3-1 is used for running the SPSM as a generator. In a generator, the
machine has to be rotated at a constant speed (synchronous speed) using a prime mover. To
achieve this condition, in the motion setup of the FE model, the mechanical transients are
removed and only a constant speed that is required can be given for the model. This way the
model is made to rotate at a required constant speed. This is shown in Figure 3-7. Figure 3-8
39
shows the constant speed of 1800 RPM given to the generator which is the synchronous speed
required to produce 60Hz sinusoidal three phase voltages. Since no voltage has to be given to the
stator windings, they are left alone and can be modeled in the Maxwell circuit editor to
incorporate loading of the generator. This condition is shown in Figure 3-9 where the parameters
of the stator winding (winding resistance and inductance) are entered in the Maxwell circuit
editor. The comparison of the simulation FE model and the experimental generator at different
loading conditions, different field currents and different loading circuits is shown in detail in
Chapter 4.
Figure 3-7. Constant Speed - Prime mover setting
40
Figure 3-8. Constant speed of 1800 RPM
Figure 3-9. Circuit for generator with R Load
41
3.3 AT (ampere turn) Distribution Scheme
The flowchart in Figure 3-10 shows the step-by-step procedure of using AT (ampere turn)
distribution scheme to determine the magnetic characteristics of the material used in the Salient
pole synchronous motor. Ampere turn can also be expressed as magnetomotive force and can
determined by multiplying the turns in the winding and the amount of current flowing in a given
winding. This scheme is a novel non-destructive technique for identifying the magnetic
characteristics without using any sample material and thus can be utilized by the already installed
machines. FE modeling of the machine followed by performing experimental tests on the SPSM
helps in determining the magnetic characteristics of the actual machine.
3.3.1 Steps of AT distribution scheme
1. Perform experimental open circuit test with the real motor for different field currents
(0.1- 1.5A).
2. Perform open circuit test with the FE model of SPSM for different field currents (0.11.5A) with steel1008 material –material with known BH characteristics.
3. Magnetostatic FE simulation with a known material- steel 1008 to determine the B
(Magnetic flux density) and H (magnetic field intensity) in different parts of the iron in
the SPSM for the different field current settings
4. Calculate AT and gap contraction factor, Kg using the open circuit test voltage from the
simulation results.
5. Use the experimental open circuit voltage and find AT for the air gap using the Kg
obtained from the simulations.
6. Compare the simulated AT for different parts of the machine with the experimental
ampere turns and split the experimental ampere turns according to the same ratio. This
gives new ampere turns for different parts of the motor. Repeat this process for all 15
field currents
7. Using the calculated AT, determine the magnetic field strength for the experimental
motor and determine the new magnetic characteristics of the material.
The detailed procedure of the ampere turn distribution technique is discussed step by step in the
following sections
42
Figure 3-10. Steps in AT (ampere turn) distribution scheme
3.3.2 Open circuit test
To determine the magnetic properties of the material, an open circuit test for fifteen different
field currents from 0.1A to 1.5A, in steps of 0.1 A, was first done on the actual SPSM to obtain
the experimental open circuit characteristics (OCC) of the machine. This was followed by
performing OCC test with FE model using steel 1008 as the initial known material. An external
circuit was used to give appropriate field current of 0.1 – 1.5A as required. Appropriate
voltmeters were connected to the stator winding to measure the generated voltage. The
simulation was run for two seconds and the rms value of the simulated phase voltage was noted
for each field current. The two OCCs, one obtained from experiment and the other from the
transient simulation, showed considerable difference in the generated voltages as shown in Table
3-2. Thus it shows that using steel1008 will not be very meaningful in simulating the SPSM.
However, it was conjectured that for identical geometry, the magnetic field strength, H, required
to set up a given flux density in the different parts of the iron will be proportional for different
43
materials. Thus as the next step H was obtained through magnetostatic simulation by applying a
dc current to the field circuit and keeping the stator windings open.
S.No
Field
Generated voltage
Generated voltage
% Difference
Current (A)
using steel 1008 (V)
in experiment (V)
1
0.1
19.44
19.03
2.1
2
0.2
40.26
37.4
7.7
3
0.3
61.69
57.8
6.7
4
0.4
82.94
74.5
11.3
5
0.5
103.23
91.1
13.3
6
0.6
120.84
104.4
15.7
7
0.7
134.82
115
17.2
8
0.8
145.29
123.2
17.9
9
0.9
153.12
129.4
18.1
10
1.0
159.19
134.8
18.3
11
1.1
164.24
139.1
18.1
12
1.2
168.24
142.7
18.0
13
1.3
171.99
146.2
17.6
14
1.4
175.13
148.7
17.8
15
1.5
177.97
151.5
17.5
Table 3-2. Open circuit voltage - comparison of different materials with the experimental motor
3.3.3 Magnetostatic simulation in Ansys Maxwell
This section discusses the performance of Maxwell on magnetostatic simulations and the
determination of magnetic field intensity (H) and magnetic flux density (B) of different parts of
the motor such as core, yoke, pole and teeth of SPSM using the FE model in Figure 3-1 for
44
different field currents. To analyze the magnetic characteristic of the SPSM at different positions
the machine is rotated from 0 – 360o in steps of 5 degrees. This is achieved by giving a table of
degrees in steps to the parametric setup of the model in Optometrics as shown in Figure 3-11.
Following this, the currents in the field winding shown in pink in Figure 3-12 are set to different
field currents such as 63A, 126A, 189A, and so on to achieve field current of 0.1A, 0.2A, 0.3A
till 1.5A. There are 630 conductors in the field winding which is shown as one lumped winding
in the FE model. Therefore a multiplication factor of 630 is used for the field currents to
represent the necessary ampere turns. This is shown in Table 3-3. Furthermore, the solution type
of the model is specified as Magnetostatic. This way the magnetostatic effect of the SPSM can
be studied and the B, H for different parts of the SPSM can be calculated at different field
currents.
Figure 3-11. Optometrics setup
45
re
Yo
ke
th
Co
o
To
Pole
Figure 3-12. Field winding (Pink) in SPSM
Table 3-3 shows the field current specified in the FE model for the field windings to the actual
field current flowing in the field windings in SPSM.
S.No.
FE model field current (A)
Actual field current (A)
1
63
0.1
2
126
0.2
3
189
0.3
4
252
0.4
5
315
0.5
6
378
0.6
7
441
0.7
8
504
0.8
9
567
0.9
10
630
1.0
11
693
1.1
12
756
1.2
46
13
819
1.3
14
882
1.4
15
945
1.5
Table 3-3. Field current - FE
Using Figure 3-11 and by setting the solution type to Magnetostatic solution, simulations were
done to analyze the SPSM under 15 different field currents. With a computer using Intel i7 core
with 3.4GHz frequency and 16GB RAM, it took 3 hours to complete one simulation. These
simulations give a B and H plot inside the SPSM. The values of H were manually calculated by
looking at the result plots of B and H in comparison with their scales. These computations and
plots are shown below. The material used for the simulation was steel1008. This material was
chosen because it was a known material available in Ansys and the machine is assumed to have a
magnetic material which has fairly similar magnetic characteristics compared to the original
material in the real SPSM. The magnetic characteristics of the original material used in the
SPSM will be computed based on these FE simulations and the OCC tests.
Figure 3-13. Plot of H for 0.5A Field Current
47
Figure 3-14. Plot of B for 0.5A Field Current
Table 3-4 shows the magnetic field strength (H) calculated from the magnetostatic simulation of
SPSM for different parts of the motor at different field currents. H for different parts was
determined using the “modify attributes” tab available in the Ansys Maxwell.
Field current (A)
H for Core
H for Yoke
H for Pole
H for Teeth
0.1
56.5
115
54.11
78
0.2
92.5
180
102.86
106.25
0.3
102.5
225
109.13
130
0.4
172.5
400
165.61
214
0.5
214
600
196.28
291.25
0.6
239.6
800
228.42
368.75
0.7
350
2000
301.25
393
0.8
367.31
4000
320.33
490
0.9
380
8250
389.11
600
1.0
387.5
17500
339.17
680
1.1
395
27000
423.61
900
1.2
407.5
30000
483.89
1000
1.3
495
40000
496.33
1275
1.4
505
50000
661.49
1162.5
1.5
510
55000
669.56
1258.33
Table 3-4. Magnetic field intensity (AT/m) of Core, Yoke, Pole, Teeth of SPSM
48
The method used for the calculation of magnetic field strength is as follows:
1. Plot the Magnetostatic result for H.
2. Modify the plot scale of H appropriately using “modify attribute tab” and zoom into one
region of the SPSM (core, yoke, pole or teeth) and determine the value of H for different
iron regions accurately.
The above procedure is followed for the fifteen different field currents from 0.1 to 1.5A and the
values of H was calculated accordingly and tabulated in Table 3-4. This method is accurate when
performed at low field currents. But when the field currents become higher, the value of B and H
increase. When the values become higher, the accuracy decreases. The scale shown in Figure
3-15 obtained from the modify attributes tab in the result has to be varied to perform the
calculation of H. If the Min and Max shown in Figure 3-15 are varied appropriately, the accuracy
can be improved.
Figure 3-15. Modify attribute tab in magnetostatic simulation
49
3.3.4 Calculation of ampere turns for different parts of the
motor:
The salient pole synchronous machine under considerations has the following dimensions and
parameters based on the manufacturer’s datasheets. The lengths of different parts of the Machine
are shown in Table 3-5.
Part of the Machine
Length (mm)
Air Gap
0.6
Core
88.63
Yoke
50
Teeth
27.8
Pole
47.8
Table 3-5. Length of different parts of the SPSM
Magnetic Field strength (H) is defined as follows:
(3.1)
where
N – Number of turns
I – Current flowing in that area
– Path length of the magnetic field
Number of turns, N multiplied by current, I (NI) is usually referred to as Ampere Turns (AT)
Using the value of H and , ampere turns can be calculated for different parts of the machine.
This is shown in Table 3-6..
Part of the Machine
H (AT/m)
L (mm)
AT (HL)
Core
387.5
88.63
34.34
Yoke
17500
50
87.5
Teeth
339.1667
27.8
9.42
Pole
680
47.8
32.5
Table 3-6. Ampere Turn for Field Current of 1A
50
All the calculations shown below are at a field current of 1A. Similar procedure is used for field
currents from 0.1 to 1.5A.
(3.2)
where
= 630 and
= 1A thereby giving
to be equal to 630.
From the calculations showed in
Table 3-6 and using 3.3, it can be seen that ampere turn of the air gap
can be calculated as:
(3.3)
where
- Total field ampere turns
- Ampere turns of the core
- Ampere turns of the yoke
- Ampere turns of the pole
- Ampere turns of the teeth
The formula shown in 3.3 is explained pictorially on Figure 3-16. This figure is the electrical
equivalent of the magnetic circuit which is expressed using magnetomotive force. Kirchoff’s
voltage law can be used to express the equation 3.3. It can be equivalently expressed using
ampere law shown by
(3.4)
51
Figure 3-16. Ampere turn distribution in SPSM
To calculate magnetic flux density (B) of the air gap for simulation using steel1008 material,
Open circuit voltage of the SPSM is required. The equation to find Bg [24] is given by (3.4)
(3.5)
where
– Phase voltage in OCC
– Winding factor
– Field form factor
– Length of the air gap
– Depth of the pole (76mm)
– Pole pitch
– Frequency (60Hz)
Of these,
is known from the simulation using steel1008 material.
is known directly
from the manufacturer’s data. These values are shown in Table 3-5.
52
Winding factor,
= 0.96 * 0.866
= 0.8314
Field form factor,
= 0.654
Pole Pitch,
=
= 0.1162 m
Using these values, the value of the magnetic flux density for the air gap was
T
With ampere turns
using (3.5), where
known for the air gap, the gap contraction factor
is the length of air-gap and
can be determined
is the permeability of air.
(3.6)
= 1.168
This
obtained from the FE simulations is then used to determine the ampere turn of air gap,
for the experimental machine.
3.3.5 Calculation of magnetic flux density from the
experiment data
To determine the magnetic flux density of different parts of the machine, flux per phase has to be
calculated. Following the determination of flux, ampere turn of the air gap for the experiment is
53
computed using the gap contraction factor calculated from the simulation. These calculations are
shown below:
Flux per phase,
is shown by the formula [24]
(3.7)
= 0.00421Wb
Once flux per phase is calculated, ampere turn of the air gap is calculated from (3.6)
(3.8)
where
is calculated using (3.5) as 0.7T,
is known directly and
is known from the
simulation (3.6). With these values,
AT
The calculations below show the determination of magnetic field intensity (B) for the
experimental machine at 1A field current. Similar procedure is performed for fifteen different
field currents from 0.1A to 1.5A.
3.3.5.1
Core
Magnetic flux density of the core Bc is defined as follows:
(3.9)
where
is the flux per phase and
is the area of the core.
= 0.0222*0.0684
= 0.00152 m2
= 1.384 T
54
3.3.5.2
Yoke
Magnetic flux density of the yoke By is defined as follows:
(3.10)
where
is the flux per phase and
is the area of the yoke.
= 0.0146*0.076
= 0.00111 m2
= 1.895 T
3.3.5.3
Pole
Magnetic flux density of the core Bp is defined as follows:
(3.11)
where
is the flux per phase and
is the area of the core.
= 0.044*0.0684
= 0.0030 m2
= 1.394 T
3.3.5.4
Teeth
Magnetic flux density of the core Bt is defined as follows:
(3.12)
where
is the flux per phase and
is the area of the core.
55
= 0.0078*0.0684
= 0.00314 m2
= 1.34 T
Once, B was calculated for the experiment, the determination of H would give the magnetic
characteristics of the material. The procedure to determine the magnetic field intensity is shown
below. Since H will be proportional across different parts of the iron for different materials, this
characteristic is utilized to determine the H across different parts for the actual machine. Since H
is proportional, ampere turns will also be proportional from (3.1). From the FE simulations at 1A
field current, Ampere Turns for different parts of the SPSM are shown in Table 3-7.
Part of Motor
Ampere Turns
Air gap
466.23
Core
34.34
Yoke
87.5
Teeth
9.43
Pole
32.5
Table 3-7. Ampere turns from FE simulation
Once FE Simulation was over and the ampere turn distribution was found, these readings where
used to determine percentage split of ampere turns between different parts of the actual Machine.
This is shown in Table 3-8.
56
Location
(AT)
Field
630
Ratio (based on column 2)
(AT)
630
Core
Yoke
Teeth
Pole
Iron
Air Gap
Table 3-8 . Estimated distribution of ampere turns for the actual machine
The calculations performed in Table 3-8 have been explained in Figure 3-17.
57
Figure 3-17. Ampere turn distribution steps shown in Table 3-8
Once the ampere turn distribution was found, using (3.1), magnetic field intensity was calculated
as shown in Table 3-9.
Part
AT
l (mm)
H (AT/l)
Core
49.74
88.63
561.28
Yoke
126.74
50
25348.30
Teeth
13.65
27.8
491.27
Pole
47.08
47.8
984.96
Air gap
392.77
0.6
654622.12
Table 3-9. Magnetic field intensity for actual machine
58
Using the same procedure, the magnetic field intensity and magnetic flux density were calculated
for fifteen different field currents. Their values are shown in Table 3-10, Table 3-11, Table 3-12
and Table 3-13.
S.No
Field Current (A)
B (T)
H (AT/m)
1
0.1
0.195
64.06
2
0.2
0.3804
107.11
3
0.3
0.59
167.72
4
0.4
0.76
303.78
5
0.5
0.93
393.44
6
0.6
1.07
470.08
7
0.7
1.17
646.23
8
0.8
1.26
652.88
9
0.9
1.32
623.76
10
1.0
1.38
561.29
11
1.1
1.43
524.68
12
1.2
1.467
545.42
13
1.3
1.5
614.63
14
1.4
1.53
589.24
15
1.5
1.56
615.98
Table 3-10. BH for core
59
S.No
Field Current (A)
B (T)
H (AT/m)
1
0.1
0.267
130.38
2
0.2
0.521
218.01
3
0.3
0.808
368.18
4
0.4
1.04
704.42
5
0.5
1.27
1103.1
6
0.6
1.46
1569.54
7
0.7
1.61
3692.7
8
0.8
1.72
7109.78
9
0.9
1.81
13542.12
10
1.0
1.89
25348.3
11
1.1
1.95
35864.21
12
1.2
2.01
40153.38
13
1.3
2.05
49666.5
14
1.4
2.09
60745.4
15
1.5
2.13
66428.65
Table 3-11. BH for Yoke
60
S.No
Field Current (A)
B (T)
H (AT/m)
1
0.1
0.189
61.35
2
0.2
0.368
102.58
3
0.3
0.571
178.57
4
0.4
0.737
291.65
5
0.5
0.90
360.85
6
0.6
1.03
448.14
7
0.7
1.13
556.21
8
0.8
1.22
569.38
9
0.9
1.28
638.72
10
1.0
1.34
491.28
11
1.1
1.38
562.68
12
1.2
1.42
647.65
13
1.3
1.45
616.28
14
1.4
1.48
803.65
15
1.5
1.51
808.68
Table 3-12. BH for Teeth
61
S.No
Field Current (A)
B (T)
H (AT/m)
1
0.1
0.1965
88.44
2
0.2
0.383
147.87
3
0.3
0.595
212.74
4
0.4
0.766
376.87
5
0.5
0.937
535.47
6
0.6
1.07
723.47
7
0.7
1.18
725.47
8
0.8
1.27
870.95
9
0.9
1.33
984.8
10
1.0
1.39
984.96
11
1.1
1.44
1195.48
12
1.2
1.48
1070.76
13
1.3
1.51
1583.12
14
1.4
1.54
1412.33
15
1.5
1.57
1519.8
Table 3-13. BH for Pole
62
3.4 Comparison of Steel1008, M27 and the new material
From the above tables, it can be seen that BH characteristics shows maximum saturation and
goes till high values of magnetic field strength and intensity for the yoke of the SPSM. Since the
machine experiences high levels of B and H in the yoke region, the characteristic of yoke was
chosen as the magnetic characteristics of the material used in SPSM. This is because, the rotor
material is unknown as mentioned in Section 1.3.The comparison of the BH characteristics of
steel and the newly determined magnetic characteristics is shown in Figure 3-18 and Figure 3-19.
Magnetic Flux Density vs Magnetic Field Intensity for the Material
2.5
Magnetic Flux Density (T)
2
Steel1008
New BH Curve
1.5
1
0.5
0
0
1
2
3
4
5
Magnetic Field Strength (A/m)
6
7
4
x 10
Figure 3-18. BH steel1008 vs New material
If the characteristics of the new BH curve are observed closely, it can be seen that a sudden
increase is seen at B = 1.8T and H = 4*104 AT/m. The reason for such an increase is mainly
because of the disadvantages involved in determining the accurate values of H from the
magnetostatic simulation. At higher field currents, the accuracy of determination of H decreases.
When using the modify attribute tab shown in 3.3.2, the scale of H is varied between different
values to zoom in one portion of the SPSM such as the core, yoke, pole or the teeth. Since the
value of H is higher at higher field currents, the range of H is also high. Therefore doing the
63
pixel by pixel calculation will not be very accurate. This can be a cause for the sudden increase
seen at 1.8T.
Magnetic Flux Density vs Magnetic Field Intensity for different parts of the motor
1.4
Magnetic Flux Density (T)
1.2
1
0.8
0.6
Core
Teeth
Pole
0.4
0.2
0
0
50
100
150 200 250 300 350
Magnetic Field Intensity (A/m)
400
450
Figure 3-19. BH plot of different parts of SPSM based on Table 3-9, 3-11 and 3-12
Once the new characteristics were determined, FE simulations were done with the newly
determined material and compared with steel1008 and M27 material. M27 material was chosen
for comparison since the stator to the actual motor was made with M27. The Table 3-14 shows
the comparison of OCC between steel1008, new material and M27. They have also been plotted
in Figure 3-20. Figure 3-21 shows the exact difference in voltage between the experimental OCC
and generated OCC using M27 and steel1008.
64
S.No
Field Current
(A)
Estimated magnetic
Steel1008 (V)
material (new material)
M27 (V)
Experiment (V)
(V)
1
0.1
19.44
17.75
19.77
19.03
2
0.2
40.26
35.97
39.57
37.4
3
0.3
61.69
53.79
59.3
57.8
4
0.4
82.94
71.4
78.93
74.5
5
0.5
103.23
87.92
97.77
91.1
6
0.6
120.84
102.9
112.97
104.4
7
0.7
134.82
115.6
124.13
115
8
0.8
145.29
125.68
132.88
123.2
9
0.9
153.12
133.11
139.88
129.4
10
1.0
159.19
138.85
145.23
134.8
11
1.1
164.24
143.43
149.19
139.1
12
1.2
168.24
148.43
152.28
142.7
13
1.3
171.99
152.65
154.91
146.2
14
1.4
175.13
156.37
157.26
148.7
15
1.5
177.97
159.78
159.42
151.5
Table 3-14. Comparison of open circuit voltage for different materials
65
Generated voltage vs Field current
180
Experiment
New BH curve
Steel 1008
M27
160
140
Voltage (V)
120
100
80
60
40
20
0
0
0.5
1
1.5
Field current (A)
Figure 3-20. Comparison of generated voltage
Difference in Voltage between Steel1008, New
material and M27 with the Experiment
30.00
Difference (V)
25.00
20.00
15.00
Difference New material
10.00
Difference - M27
Difference Steel1008
5.00
0.00
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5
Field Current (A)
Figure 3-21. Comparison of OCC difference - Steel1008, M27 and new Material from the experimental
OCC
66
3.5 Conclusion
It can be clearly seen from Figure 3-20 and Figure 3-21 that the newly determined material
showed close similarity to the experimental results than M27 and Steel1008 material. It has to be
noted that the new material has been used for the stator and rotor of the SPSM. The stator of the
real SPSM is made of M27 and the rotor is made of some cold rolled steel and its characteristics
of the material are not known. This is because under steady state, the rotor rotates at the same
speed as the rotating magnetic field caused by the stator current. Therefore dynamo grade steel
with good quality and low losses is not required for the rotor. Also more eddy current losses
under transient condition will provide better damping and hence increase the transient stability of
the machine. This is why M27 when used for both the stator and the rotor did not give good
results. But the new material combines the characteristics of the M27 and the unknown material
used in the rotor to form average magnetic characteristics, which might also be a reason for the
sudden increase seen in Figure 3-18. Based on the comparison and the table, it can also be seen
that the newly determined material shows overall error less than 5% error compared to other
materials. Thus a new and novel technique to determine the magnetic characteristics has been
developed for SPSM. This technique is non-invasive and requires minimal calculations. With the
FE modeling of SPSM in Ansys explained in detail in this chapter, this technique will be simple
and easy to implement. Therefore this technique has better merits compared to the invasive and
destructive techniques discussed in Chapter 1.
67
Chapter 4
Comparison of results with new magnetic
material and real SPSM
Using the newly determined magnetic material shown in Chapter 3, different performance tests
were conducted to evaluate the new magnetic material and its characteristics in a salient pole
synchronous machine (SPSM). SPSM was run as a motor under different field conditions and
different loads. Then the SPSM was run as a generator under different field conditions and loads.
The results obtained from the experiments have been presented in this chapter.
The effects of temperature on the characteristics and performance of the electrical machine have
not been studied in this thesis. From [24] and [25], it can be seen that the highest insulation level
temperature is at 1550C (Class F). There is considerable difference in the BH characteristics of a
magnetic material when there is a temperature of 6500C to 7500C applied for one hour as shown
in [26]. Since the electrical machine should not be operated above 1550C because of the
insulation constraint, the effect of temperature on the magnetic characteristics can be neglected.
Machine tolerances and errors in terms of the voltage and current have not been taken into the
consideration and the absolute dimensions provided by the manufacturer have been used in this
thesis.
4.1 SPSM as a Motor
The salient pole synchronous motor used in the experiment is shown in Figure 4-1. Datasheet of
the SPSM is given in the appendix section.
Figure 4-1. SPSM used in the experiments
68
The table below shows the experiments performed on the SPSM as a motor under different load
and field conditions.
S.No
Load Level
DC Field Current (A)
1
FL
0.7
2
FL
1
3
FL
1.2
4
75% FL
0.7
5
75% FL
1
6
75% FL
1.2
7
66% FL
0.7
8
66% FL
1
9
66% FL
1.2
10
50% FL
0.7
11
50% FL
1
12
50% FL
1.2
13
33% FL
0.7
14
33% FL
1
15
33% FL
1.2
16
NL
0.7
17
NL
1
18
NL
1.2
Table 4-1. Motor experiments
where
FL – Full Load
NL – No Load
69
4.2 Comparison of Experiment and FE at different load
conditions with SPSM as a Motor
The SPSM was run as a motor at different load and field conditions and the same condition was
simulated in Ansys Maxwell using two different magnetic materials discussed in Chapter 3. Two
different magnetic materials used for comparison with the experimental data were M27 and the
newly determined magnetic material obtained from the ampere turn distribution scheme. The
results were compared to the experimental results.
Different field conditions (above and below the rated field current) were chosen such that the
motor operates in both leading and lagging power factors. Lagging power factor was achieved by
decreasing the field current to 0.7A which is below the rated field current of 1A and leading
power factor was achieved by increasing the field current above the rated field current at 1.2A.
The results of SPSM under these different conditions are shown below.
The figures shown below for stator currents from Figure 4-2 to Figure 4-13 have been plotted by
matching two cycles of stator current from the experiment with two cycles of stator current from
FE simulations of SPSM as a motor using M27 and the new material.
4.2.1 Full Load condition
Simulated RMS line
Simulated RMS line
current with M27
current with the New
material (A)
Material (A)
7.86
7.2
7.5
1
7.08
6.75
6.65
1.2
7.31
7.07
7.24
DC Field Current
Experimental RMS
(A)
line current (A)
0.7
Table 4-2. Stator current of the motor at FL condition
70
DC Field Current
(A)
Experimental PF
PF with M27
PF with new
Material
material
0.7A
0.89
0.95
0.90
1A
0.99
0.96
0.99
1.2A
0.96
0.78
0.90
Table 4-3. Power factor at FL condition
SPSM as motor at full load and 0.7A field current
15
New material
M27
Experiment
Stator current (zoomed)
Stator current (A)
10
5
0
-5
-10
-15
0
0.005
0.01
0.015
0.02
0.025
0.03
Time (s)
Figure 4-2. Stator current of SPSM at FL at 0.7A field current
71
SPSM as motor at full load and 0.7A field current
New material
M27
Experiment
12
Stator current (A)
11
10
9
8
7
6
0.018
0.019
0.02
0.021
0.022
0.023
Time (s)
Figure 4-3. Stator current of SPSM at FL - zoomed in version of Figure 4-2
4.2.2 75% Full Load condition
Simulated RMS
Simulated RMS line
line current with
current with the New
M27 material (A)
Material (A)
5.46
5.17
5.36
1A
5.34
5.69
5.44
1.2A
5.97
6.78
6.38
DC Field Current
Experimental RMS
(A)
line current (A)
0.7A
Table 4-4. Stator current of the motor at 75% FL condition
72
DC Field Current
(A)
Experimental PF
PF with M27
PF with new
Material
material
0.7A
0.95
0.992
0.97
1A
0.97
0.87
0.93
1.2A
0.87
0.72
0.79
Table 4-5. Power factor at 75% FL condition
SPSM as motor at 75% full load and 1A field current
15
New material
M27
Experiment
Stator current (zoomed)
10
Stator current (A)
5
0
-5
-10
-15
0
0.005
0.01
0.015
0.02
0.025
0.03
Time (s)
Figure 4-4. Stator current of SPSM at 75% FL at 1A field current
73
SPSM as motor at 75% full load and 1A field current
12
New material
M27
Experiment
11
Stator current (A)
10
9
8
7
6
5
4
0.018
0.019
0.02
0.021
0.022
0.023
0.024
Time (s)
Figure 4-5. Stator current of SPSM at 75% FL - zoomed in version of Figure 4-4
4.2.3 66% Full Load condition
Experimental
Simulated RMS
Simulated RMS line
RMS line current
line current with
current with the New
(A)
M27 material (A)
Material (A)
0.7A
4.54
4.61
4.69
1A
4.69
5.39
5.05
1.2A
5.5
6.55
6.1
DC Field
Current (A)
Table 4-6. Stator current of the motor at 66% FL condition
74
DC Field Current
(A)
Experimental PF
PF with M27
PF with new
Material
material
0.7A
0.96
0.997
0.98
1A
0.92
0.82
0.89
1.2A
0.79
0.67
0.73
Table 4-7. Power factor at 66% FL condition
SPSM as motor at 66% full load and 1.2 A field current
15
New material
M27
Experiment
Stator current (zoomed)
Stator current (A)
10
5
0
-5
-10
-15
0
0.005
0.01
0.015
0.02
0.025
0.03
Time (s)
Figure 4-6. Stator current of SPSM at 66% FL at 1.2A field current
75
SPSM as motor at 66% full load and 1.2 A field current
11
New material
M27
Experiment
10
Stator current (A)
9
8
7
6
5
0.018
0.0185
0.019
0.0195
0.02
0.0205
0.021
0.0215
0.022
0.0225
0.023
Time (s)
Figure 4-7. Stator current of SPSM at 66% FL - zoomed in version of Figure 4-6
4.2.4 50% Full Load condition
Experimental
Simulated RMS
Simulated RMS line
RMS line current
line current with
current with the New
(A)
M27 material (A)
Material (A)
0.7A
3.1
3.68
3.7
1A
3.69
4.89
4.46
1.2A
4.7
5.92
5.69
DC Field Current
(A)
Table 4-8. Stator current of the motor at 50% FL condition
76
DC Field Current
(A)
Experimental PF
PF with M27
PF with new
Material
material
0.7A
0.97
0.992
0.99
1A
0.85
0.71
0.8
1.2A
0.68
0.44
0.62
Table 4-9. Power factor at 50% FL condition
SPSM as motor at 50% full load and 1A field current
10
8
New material
M27
Experiment
Stator current (zoomed)
6
Stator current (A)
4
2
0
-2
-4
-6
-8
-10
0
0.005
0.01
0.015
0.02
0.025
0.03
Time (s)
Figure 4-8. Stator current of SPSM at 50% FL at 1A field current
77
SPSM as motor at 50% full load and 1A field current
7.5
New material
M27
Experiment
7
Stator current (A)
6.5
6
5.5
5
4.5
4
3.5
3
0.018
0.019
0.02
0.021
0.022
0.023
Time (s)
Figure 4-9. Stator Current of SPSM at 50% FL - zoomed in version of Figure 4-8
4.2.5 33% Full Load condition
Experimental
Simulated RMS
Simulated RMS line
RMS line current
line current with
current with the
(A)
M27 material (A)
New Material (A)
0.7A
1.53
2.81
2.69
1A
2.62
4.12
3.91
1.2A
4.01
5.46
5.29
DC Field Current
(A)
Table 4-10. Stator current of the motor at 33% FL condition
78
DC Field Current
Experimental PF
(A)
PF with M27
PF with new
Material
material
0.7A
0.92
0.93
0.99
1A
0.5
0.41
0.65
1.2A
0.34
0.37
0.48
Table 4-11. Power factor at 33% FL condition
SPSM as motor at 33% full load and 0.7A field current
10
New material
M27
Experiment
8
6
Stator current (zoomed)
Stator current (A)
4
2
0
-2
-4
-6
-8
-10
0
0.005
0.01
0.015
0.02
0.025
0.03
Time (s)
Figure 4-10. Stator current of SPSM at 33% FL at 0.7A field current
79
SPSM as motor at 33% full load and 0.7A field current
New material
M27
Experiment
4.5
4
Stator current (A)
3.5
3
2.5
2
1.5
1
0.5
0.016
0.017
0.018
0.019
0.02
0.021
0.022
0.023
0.024
0.025
Time (s)
Figure 4-11. Stator current of SPSM at 33% FL - Zoomed in version
4.2.6 No Load condition
Simulated RMS
Experimental
Simulated RMS
RMS line current
line current with
(A)
M27 material (A)
0.7A
0.9
1.49
1.09
1A
2.29
3.93
3.27
1.2A
3.68
5.49
4.85
DC Field
Current (A)
line current with
the New Material
(A)
Table 4-12. Stator current of the motor at NL condition
80
DC Field Current
(A)
Experimental PF
PF with M27
PF with New
Material
Material
0.7A
0.72
0.48
0.72
1A
0.34
0.14
0.2
1.2A
0.2
0.1
0.12
Table 4-13. Power factor at NL condition
SPSM as motor at no load and 1.2A field current
10
New material
M27
Experiment
Stator current (zoomed)
8
6
Stator current (A)
4
2
0
-2
-4
-6
-8
-10
0
0.005
0.01
0.015
0.02
0.025
0.03
Time (s)
Figure 4-12. Stator current of SPSM at NL at 1.2A field current
81
SPSM as motor at no load and 1.2A field current
New material
M27
Experiment
9
Stator current (A)
8
7
6
5
4
0.018
0.019
0.02
0.021
0.022
0.023
Time (s)
Figure 4-13. Stator Current of SPSM at NL - Zoomed in version
Figure 4-14, Figure 4-15 and Figure 4-16 shows the comparison of stator current at 0.7A, 1A and
1.2A field current respectively at varying load conditions such as NL, 33% FL, 50% FL, 66% FL,
75% FL and 100% FL. Figure 4-17, Figure 4-18 and Figure 4-19 shows the comparison of
power factor at 0.7A, 1A and 1.2A respectively at varying load conditions such as NL, 33% FL,
50% FL, 66% FL, 75% FL and 100% FL.
Comparison of stator current at 0.7A field current
8
New material
M27
Experiment
7
Stator current (A)
6
5
4
3
2
1
0
0
10
20
30
40
50
60
70
80
90
100
Load condition in terms of percentage of full load
Figure 4-14. Comparison of stator current at 0.7A field current
82
Comparison of stator current at 1A field current
8
New material
M27
Experiment
Stator current (A)
7
6
5
4
3
2
0
10
20
30
40
50
60
70
80
90
100
Load condition in terms of percentage of full load
Figure 4-15. Comparison of stator current at 1A field current
Comparison of stator current at 1.2A field current
8
New material
M27
Experiment
7
Stator current (A)
6
5
4
3
2
1
0
0
10
20
30
40
50
60
70
80
90
100
Load condition in terms of percentage of full load
Figure 4-16. Comparison of stator current at 1.2A field current
From Figure 4-14, Figure 4-15 and Figure 4-16, it can be seen that stator current obtained from
the new material is closer to the experiment as compared to M27.
83
Comparison of Power factor at 0.7A field current
1
Lagging Power factor
0.9
0.8
New Material
M27
Experiment
0.7
0.6
0.5
0.4
0
10
20
30
40
50
60
70
80
90
100
Load condition in terms of percentage of full load
Figure 4-17. Comparison of power factor at 0.7A field current
Comparison of Power Factor at 1A field current
1
0.9
Unity/Leading Power factor
0.8
0.7
0.6
New material
M27
Experiment
0.5
0.4
0.3
0.2
0.1
0
10
20
30
40
50
60
70
80
90
100
Load condition in terms of percentage of full load
Figure 4-18. Comparison of power factor at 1A field current
84
Comparison of Power Factor at 1.2A field current
1
New material
M27
Experiment
0.9
Leading Power factor
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
10
20
30
40
50
60
70
80
90
100
Load condition in terms of percentage of full load
Figure 4-19. Comparison of power factor at 1.2A field current
From Figure 4-17, Figure 4-18 and Figure 4-19, it can be seen that power factor obtained from
the new material is closer to the experiment as compared to M27. At 0.7A field current, the
SPSM shows lagging power factor for all loads. At 1A field current, the SPSM shows unity
power factor at full load and leading power factor for the remaining loads. At 1.2A field current,
the SPSM shows leading power factor for all the loading conditions.
From the comparison of stator current of SPSM between the experiment and FE simulation using
M27 material and new magnetic material shown in Figure 4-14, Figure 4-15 and Figure 4-16 , it
can be clearly shown that the FE simulation with the new magnetic material gives closer results
to the experiment than M27. Furthermore from Table 4-14, as the load decreases the results for
FE simulations shows higher difference especially at NL and 33% full load compared to the
experiment for both M27 and the new magnetic material. For 50% full load, the difference in the
stator current between the the new material and the experiment is around 20%. But at higher
loads such as 66% full load, 75% full load and 100% full load, the FE results are comparable to
the experiment. These large differences can be attributed to the accuracy level in the
determination of open circuit voltage for the new material and M27 seen from the last figure in
Chapter 3.
Material
M27
New material
Field
Load
Current
NL
0.7A
1A
1.2A
0.7A
1A
1.2A
-66.79
-71.12
-49.05
-22.01
-42.38
-31.67
85
33% FL
-82.86
-57.25
-36.05
-75.05
-49.24
-31.81
50% FL
18.71
32.64
25.96
19.35
20.98
21.06
66% FL
1.62
15.01
19.16
3.27
7.19
9.89
75% FL
5.30
6.62
13.82
1.82
1.94
7.11
100% FL
8.39
4.71
3.33
4.58
6.12
1
Table 4-14. Percentage deviation of stator current from the experiment for M27 and new material
4.3 Harmonic analysis of the stator current in SPSM as a
motor
Once the SPSM was run as a motor, fast fourier transform (FFT) was performed on the currents
obtained from the Real Motor and from the FE simulation of SPSM using M27 and the new
magnetic material. FFT was performed on the one second of stator current using the inbuilt
matlab function “fft”. The sampling rate used for performing FFT was 3600Hz and was
performed on one second steady state data. The results from the FFT of the stator current are
shown below.
FFT of stator current of SPSM - experimental motor
0
Stator current (dB)
-20
-40
-60
-80
-100
-120
0
200
400
600
800
1000
1200
1400
1600
1800
Frequency (Hz)
(a)
86
FFT of stator current of SPSM - FE simulation with new material
0
-20
Stator current (dB)
-40
-60
-80
-100
-120
-140
-160
-180
0
200
400
600
800
1000
1200
1400
1600
1800
Frequency (Hz)
(b)
FFT of stator current of SPSM - FE simulation with M27
0
-20
Stator current (dB)
-40
-60
-80
-100
-120
-140
-160
-180
0
200
400
600
800
1000
1200
1400
1600
1800
Frequency (Hz)
(c)
Figure 4-20. FFT of stator current (a) Experimental SPSM (b) FE simulation of SPSM with new
material (c) FE simulation of SPSM with M27
87
Frequency (Hz)
Experimental (dB)
New material (dB)
M27 (dB)
180
-39.49
-48.9
-59.87
300
-30.06
-31.74
-37.47
420
-44.13
-55.29
-41.73
540
-52.85
-52.35
-65.66
660
-39.96
-44.65
-43
780
-46.37
-54.19
-48.24
900
-61.21
-58.17
-61.18
1020
-47.84
-29
-26.81
1140
-50.85
-34.65
-30.52
1260
-61.61
-51.2
-61.82
1380
-58.62
-45.28
-44.1
1500
-59.72
-43.65
-42.87
1620
-61.44
-52.46
-62.36
1740
-66.02
-56.46
-57.33
Table 4-15. Spectrum analysis of the stator current of SPSM
Figure 4-20 shows the FFT analysis of the Stator current of SPSM as a motor at full load and 1A
field current (rated condition). It can be seen from the FFT that the spectral components of
experimental condition show closer similarities to the new magnetic material for lower order
harmonics such as 180Hz, 300Hz, 540Hz. For higher order harmonics, both M27 and the new
material show considerable difference. Lower order harmonics are highly important and play a
major role in the condition monitoring of the electrical machines. To determine the better of
these two materials for SPSM, root mean square of the difference was chosen and calculated. It
was found that the new material has a root mean square error to be 2.89 while for M27, it is 3.25.
This again shows the advantage of deriving the magnetic material using the ampere turn
distribution scheme. For the motor current signature analysis widely used in the condition
monitoring of motors, modeling of electrical machine and the material used plays a vital role in
determining the fault and its severity. Some of the irregularities in the components such as
88
180Hz can be attributed to the FE solver error and the natural disturbances and noises available
in the real condition of SPSM.
4.4 SPSM as a generator
The experimental setup used for running the SPSM as a motor is shown in Figure 4-21.
Figure 4-21 – Experimental set up of the generator
The table below shows the experiments performed on the SPSM as a generator under different
load and field conditions. The rated field current for the SPSM as a generator was 0.9A.
Therefore three different field currents 0.72A (20% below rated field current), 0.9A (rated field
current) and 1.08A (20% above rated field current) were chosen.
S.No
Load level
DC Field Current (A)
1
FL
0.72
2
FL
1
89
3
FL
1.08
4
75FL
0.72
5
75FL
1
6
75FL
1.08
7
66FL
0.72
8
66FL
1
9
66FL
1.08
10
50FL
0.72
11
50FL
1
12
50FL
1.08
13
25FL
0.72
14
25FL
1
15
25FL
1.08
16
NL
0.72
17
NL
1
18
NL
1.08
Table 4-16. Generator experiments
These experiments were performed using R, RL and RC load to induce lagging power factor
(RL), leading power factor (RC) and unity power factor loads (R). R load provided unity power
factor load while RL load produces lagging power factor load and RC produces leading power
factor load. By doing this, different field conditions were compared between experiment and FE
simulations.
4.4.1 Generator with Resistive Load
The tables and figures below shows the comparison of phase voltage generated by the
experimental SPSM and FE simulation of the same with M27 and the new material under R load.
90
Experimental
Phase voltage with
Phase voltage with
phase voltage (V)
M27 material (V)
new material (V)
0.72A
104.31
109.54
101.14
0.9A
119.2
127.67
121
1.08A
129.02
140.24
134.96
Field Current (A)
Table 4-17. Phase voltage at FL as a generator for R load
Experimental
Phase voltage with
Phase voltage with
phase voltage (V)
M27 material (V)
new material (V)
0.72A
111.39
118.46
109.64
0.9A
124.53
134.53
128.09
1.08A
133.89
145.59
139.59
Field Current (A)
Table 4-18. Phase voltage at 75% FL as a generator for R load
Experimental
Phase voltage with
Phase voltage with
phase voltage (V)
M27 material (V)
new material (V)
0.72A
114.97
120.74
111.96
0.9A
127.14
136.27
129.79
1.08A
135.99
146.59
140.71
Field Current (A)
Table 4-19 - Phase voltage at 66% FL as a generator for R load
91
Experimental
Phase voltage with
Phase voltage with
phase voltage (V)
M27 material (V)
new material (V)
0.72A
116.59
122.68
113.97
0.9A
129.19
137.71
131.13
1.08A
137.59
147.54
141.65
Field Current (A)
Table 4-20. Phase voltage at 50% FL as a Generator for R load
Experimental
Phase voltage with
Phase voltage with
phase voltage (V)
M27 material (V)
new material (V)
0.72A
119.21
125.47
116.86
0.9A
130.63
139.8
132.95
1.08A
138.66
148.87
143
Field Current (A)
Table 4-21. Phase voltage at 25% FL as a generator for R load
SPSM as a generator at 50% full load and 0.9A field current - R load
Voltage (zoomed)
200
New material
M27
Experiment
150
Generated voltage (V)
100
50
0
-50
-100
-150
-200
0
0.005
0.01
0.015
0.02
0.025
0.03
Time (s)
Figure 4-22. Generated voltage of SPSM at 50% FL and 0.9A field current for R load
92
SPSM as a generator at 50% full load and 0.9A field current - R load
210
New material
M27
Experiment
200
Generated voltage (V)
190
180
170
160
150
140
130
120
0.0185
0.019
0.0195
0.02
0.0205
0.021
0.0215
0.022
0.0225
0.023
0.0235
Time (s)
Figure 4-23. Zoomed in version of Figure 4-22
Comparison of phase voltage for resistive load at 0.72A field current
130
New material
M27
Experiment
Phase Voltage (V)
125
120
115
110
105
100
20
30
40
50
60
70
80
90
100
Load conditions in terms of perecentage of full load
Figure 4-24. Comparison of phase voltage for R load at 0.72A field current
93
Comparison of phase voltage for resistive load at 0.9A field current
150
New material
M27
Experiment
145
Phase voltage (V)
140
135
130
125
120
115
20
30
40
50
60
70
80
90
100
Load conditions in terms of percentage of full load
Figure 4-25. Comparison of phase voltage for R load at 0.9A field current
Comparison of phase voltage for resistive load at 1.08A field current
150
New material
M27
Experiment
Phase voltage (V)
145
140
135
130
125
20
30
40
50
60
70
80
90
100
Load conditions in terms of percentage of full load
Figure 4-26. Comparison of phase voltage for R load at 1.08A field current
94
Figure 4-24, Figure 4-25 and Figure 4-26 shows the comparison of phase voltage generated by
the experimental SPSM and FE simulation from M27 and the new material for R load. It can be
seen that the phase voltage from the new material matches the experiment better compared to the
M27 material. Table 4-22 shows the percentage error in the determination of the phase voltage
generated between the experiment and FE simulation. From the table, it can be clearly seen that
the new material shows a maximum deviation of 4.6% from the experiment, while the minimum
deviation is as low as 1.5%. Also the average deviation of phase voltage for the new material is
2.5%. At the same time, the maximum deviation of phase voltage for M27 is 8.7% and minimum
deviation is 5%. The average deviation of the phase voltage for M27 is 6.85%. From these
deviation values, it can be concluded that new material is better suited to be an estimate of the
magnetic material for SPSM as a generator than M27 for R load.
Material
M27
New material
Field
0.72A
0.9A
1.08A
0.72A
0.9A
1.08A
25% FL
5.25
7.02
7.36
1.97
1.78
3.13
50% FL
5.22
6.59
7.23
2.25
1.50
2.95
66% FL
5.02
7.18
7.79
2.62
2.08
3.47
75% FL
6.35
8.03
8.59
1.57
2.86
4.26
100% FL
5.00
7.11
8.70
3.04
1.51
4.60
Load
Current
Table 4-22. Percentage deviation of phase voltage from the experiment for M27 and new material for R
load
4.4.2 Generator with Resistive-Inductive (RL) Load
Experimental
Phase voltage with
Phase voltage with new
phase voltage (V)
M27 material (V)
material (V)
0.72A
75.26
75.51
70.9
0.9A
91.61
93.6
87.9
Field Current (A)
95
1.08A
103.6
109.39
103.6
Table 4-23. Phase voltage at FL as a generator for RL load
Experimental
Phase voltage with
Phase voltage with new
phase voltage (V)
M27 material (V)
material (V)
0.72A
88.66
90.38
84.15
0.9A
106.33
110.19
103.12
1.08A
117.99
124.62
119
Field Current (A)
Table 4-24. Phase voltage at 75% FL as a generator for RL load
Experimental phase
Phase voltage with
Phase voltage with new
voltage (V)
M27 material (V)
material (V)
0.72A
95.44
97.15
89.52
0.9A
109.68
115.96
108.86
1.08A
121.47
129.77
124.14
Field Current (A)
Table 4-25. Phase voltage at 66% FL as a generator for RL load
Experimental
Phase voltage with
Phase voltage with
phase voltage (V)
M27 material (V)
new material (V)
0.72A
103.5
107.23
98.52
0.9A
118.73
124.63
117.73
1.08A
128
137.19
131.2
Field Current (A)
Table 4-26. Phase voltage at 50% FL as a generator for RL load
96
Experimental
Phase voltage with
Phase voltage with
phase voltage (V)
M27 material (V)
new material (V)
0.72A
113.03
117.24
108.34
0.9A
125.45
133.03
126.31
1.08A
135.06
143.87
137.61
Field Current (A)
Table 4-27. Phase voltage at 25% FL as a generator for RL load
SPSM as a generator at 50% full load and 0.9A field current - RL load
New material
M27
Experiment
200
Voltage (zoomed)
150
Generated voltage (V)
100
50
0
-50
-100
-150
-200
0
0.005
0.01
0.015
0.02
0.025
0.03
Time (s)
Figure 4-27. Generated voltage of SPSM at 50% FL and 0.9A field current for RL load
97
SPSM as a generator at 50% full load and 0.9A field current - RL load
200
New material
M27
Experiment
Generated voltage (V)
180
160
140
120
100
0.018
0.019
0.02
0.021
0.022
0.023
Time (s)
Figure 4-28. Zoomed in version of Figure 4-27
Comparison of phase voltage for resistive-inductive load at 0.72A field current
120
New material
M27
Experiment
115
110
Phase voltage (V)
105
100
95
90
85
80
75
70
20
30
40
50
60
70
80
90
100
Load conditions in terms of percentge of full load
Figure 4-29. Comparison of phase voltage for RL load at 0.72A field current
98
Comparison of phase voltage for resistive-inductive load at 0.9A field current
135
New material
M27
Experiment
130
125
Phase voltage (V)
120
115
110
105
100
95
90
85
20
30
40
50
60
70
80
90
100
Load conditions in terms of percentage of full load
Figure 4-30. Comparison of phase voltage for RL load at 0.9A field current
Comparison of phase voltage for resistive-inductive load at 1.08A field current
145
New material
M27
Experiment
140
Phase voltage (V)
135
130
125
120
115
110
105
100
20
30
40
50
60
70
80
90
100
Load conditions in terms of percentage of full load
Figure 4-31. Comparison of phase voltage for RL load at 1.08A field current
99
Figure 4-29, Figure 4-30 and Figure 4-31 shows the comparison of phase voltage generated by
the experimental SPSM and FE simulation from M27 and the new material for RL load. It can be
seen that the phase voltage from the new material matches the experiment better compared to the
M27 material. Table 4-28 shows the percentage error in the determination of the phase voltage
generated between the experiment and FE simulation. From the table, it can be clearly seen that
the new material shows a maximum deviation of 6.2% from the experiment, while the minimum
deviation is as low as 0%. Also the average deviation of phase voltage for the new material is
2.75%. At the same time, the maximum deviation of phase voltage for M27 is 7.18% and
minimum deviation is 0.33%. The average deviation of the phase voltage for M27 is 4.38%.
From these deviation values, it can be concluded that new material is better suited to be an
estimate of the magnetic material for SPSM as a generator than M27 for RL load.
Material
M27
New material
Field
0.72A
0.9A
1.08A
0.72A
0.9A
1.08A
25% FL
3.72
6.04
6.52
4.15
0.69
1.89
50% FL
3.60
4.97
7.18
4.81
0.84
2.50
66% FL
1.79
5.73
6.83
6.20
0.75
2.20
75% FL
1.94
3.63
5.62
5.09
3.02
0.86
100% FL
0.33
2.17
5.59
5.21
4.05
0.00
Load
Current
Table 4-28. Percentage deviation of phase voltage from the experiment for M27 and new material for RL
load
4.4.3 Generator with Resistive-Capacitive (RC) Load:
Experimental
Phase voltage with
Phase voltage with
phase voltage (V)
M27 material (V)
new material (V)
0.72A
139.13
147.78
141.3
0.9A
145.42
156.49
151.49
Field Current (A)
100
1.08A
152.19
161.75
159.64
Table 4-29. Phase voltage at FL as a generator for RC load
Experimental
Phase voltage with
Phase voltage with
phase voltage (V)
M27 material (V)
new material (V)
0.72A
136.16
144.17
136.99
0.9A
145.06
153.55
147.87
1.08A
150.44
159.06
156.37
Field Current (A)
Table 4-30. Phase voltage at 75% FL as a generator for RC load
Experimental
Phase voltage with
Phase voltage with
phase voltage (V)
M27 material (V)
new material (V)
0.72A
134.85
142.63
135.23
0.9A
142.55
152.38
146.43
1.08A
149.82
155.09
158.1
Field Current (A)
Table 4-31. Phase voltage at 66% FL as a generator for RC load
Experimental
Phase voltage with
Phase voltage with
phase voltage (V)
M27 material (V)
new material (V)
0.72A
131.29
138.98
131.25
0.9A
139.67
149.76
143.25
1.08A
146.82
155.97
152.21
Field Current (A)
Table 4-32. Phase voltage at 50% FL as a generator for RC load
101
Experimental
Phase voltage with
Phase voltage with
phase voltage (V)
M27 material (V)
new material (V)
0.72A
127.23
134.56
126.54
0.9A
136.89
146.65
139.74
1.08A
144.29
153.6
148.99
Field Current (A)
Table 4-33. Phase voltage at 25% FL as a generator for RC load
SPSM as a generator at 50% full load and 0.9A field current - RC load
250
New material
M27
Experiment
Voltage (zoomed)
200
150
Generated voltage (V)
100
50
0
-50
-100
-150
-200
-250
0
0.005
0.01
0.015
0.02
0.025
0.03
Time (s)
Figure 4-32 – Generated voltage of SPSM at 50% FL and 0.9A field current for RC load
102
SPSM as a generator at 50% full load and 0.9A field current - RC load
230
New material
M27
Experiment
220
210
Generated voltage (V)
200
190
180
170
160
150
140
130
0.0185
0.019
0.0195
0.02
0.0205
0.021
0.0215
0.022
0.0225
0.023
Time (s)
Figure 4-33 – Zoomed in version of Figure 4-32
Comparison of phase voltage for resistive-capacitive load at 0.72A field current
150
New material
M27
Experiment
Phase voltage (V)
145
140
135
130
125
20
30
40
50
60
70
80
90
100
Load conditions in terms of percentage of full load
Figure 4-34. Comparison of phase voltage for RC load at 0.72A field current
103
Comparison of phase voltage for resistive-capacitive load for 0.9A field current
160
New material
M27
Experiment
Phase voltage (V)
155
150
145
140
135
20
30
40
50
60
70
80
90
100
Load conditions in terms of percentage of full load
Figure 4-35. Comparison of phase voltage for RC load at 0.9A field current
Comparison of phase voltage for resistive-capacitive at 1.08A field current
162
New material
M27
Experiment
160
Phase voltage (V)
158
156
154
152
150
148
146
144
20
30
40
50
60
70
80
90
100
Load conditions in terms of perecentage of full load
Figure 4-36. Comparison of phase voltage for RC load at 1.08A field current
104
Figure 4-29, Figure 4-30 and Figure 4-31 shows the comparison of phase voltage generated by
the experimental SPSM and FE simulation from M27 and the new material for RC load. It can be
seen that the phase voltage from the new material matches the experiment better compared to the
M27 material. Table 4-28 shows the percentage error in the determination of the phase voltage
generated between the experiment and FE simulation. From the table, it can be clearly seen that
the new material shows a maximum deviation of 4.9% from the experiment, while the minimum
deviation is as low as 0.03%. Also the average deviation of phase voltage for the new material is
2.31%. At the same time, the maximum deviation of phase voltage for M27 is 7.61% and
minimum deviation is 5.53%. The average deviation of the phase voltage for M27 is 6.94%.
From these deviation values, it can be concluded that new material is better suited to be an
estimate of the magnetic material for SPSM as a generator than M27 for RC load.
Material
M27
New material
Field
0.72A
0.9A
1.08A
0.72A
0.9A
1.08A
25% FL
5.76
7.13
6.45
0.54
2.08
3.26
50% FL
5.86
7.22
6.22
0.03
2.56
3.66
66% FL
5.77
6.90
5.53
0.28
2.72
3.52
75% FL
5.88
5.83
5.75
0.61
1.92
3.94
100% FL
6.22
7.61
6.28
1.56
4.17
4.90
Load
Current
Table 4-34. Percentage deviation of phase voltage from the experiment for M27 and new material for RC
load
The generator has been subjected to varying condition such as different field currents above and
below its rated and also with different loads (leading, lagging) and with different loading
conditions (25%, 50%, 66% and 75% full load).
From 4.2, 4.3 and 4.4, it can be seen that the SPSM has been tested with varied environments it
might experience during its operation and the newly determined material has been effective in
determining the motor characteristics with very good accuracy. This corroborates that the
105
scheme in Chapter 3 is an effective strategy to emulate the magnetic characteristics of a material
of a SPSM with reasonable accuracy.
From the tables and figures shown in chapter 4, it can be seen the new magnetic material has
been effective in determining the characteristics of the material in the real SPSM. This is proved
by the close results achieved while running the SPSM as a motor and a generator under various
loading conditions and field currents.
Thus this chapter gives a detailed explanation on the comparison of experimental SPSM with FE
simulations using two different materials. It can be seen from these comparisons that the new
material characterizes motor accurately compared to the M27 material.
106
Chapter 5
Conclusion
5.1 Conclusion
Existing schemes of magnetic material testing such as Epstein and single sheet tester have been
discussed in detail. The advantage and the disadvantages associated with these testers have also
been discussed. Furthermore latest developments in this field have also been discussed.
Modeling of electrical machines especially SPSM using Ansys Maxwell for running it a motor
and generator has been provided. The same process can be used for modeling induction motors
and other electrical machines. Chapter 3 provides useful details and characteristics of Ansys
Maxwell in the modeling of electrical machines. The disadvantages associated with the existing
techniques have been rectified using the novel ampere turn distribution technique. The method is
simple and easy to be replicated. It is non-invasive and non-destructive and can be implemented
easily on the SPSM which has been already been installed in the industries.
Detailed
experiments on the SPSM as a motor and generator have been performed at various different
conditions to validate the ampere turn method.
5.2 Advantages and Disadvantages of the ampere turn
distribution scheme
Advantages

This is a non-invasive and non-destructive method

The calculations of B and H and the modeling of FE are simple and easy to implement.

This scheme can be implemented in the salient pole synchronous machines which have
been already installed.
Disadvantages

Computation time for FE is very high. It takes 12 hours to do a simulation of FE as a
motor and generator and 4 hours to run magnetostatic simulation for a SPSM. Therefore
this scheme is time consuming at the start of the process.
107

Determination of H from the magnetostatic simulation of SPSM in Ansys Maxwell is
another problem associated with this scheme. At high B, the accuracy of determination of
H decreases as there is no direct method for the determination of H for different parts of
the SPSM.

Another important disadvantage is the requirement of the geometry and dimensions of the
machine to be modeled. This data is not always available and might be difficult to obtain
for a specific machine.
5.3 Contributions
Non Destructive Technique
In this research work, the problem associated with the determination of magnetic characteristics
of the material used in salient pole synchronous motor (SPSM) has been addressed. Existing
schemes for the determination of magnetic characteristics have been discussed and the
disadvantages have been detailed to recognize the need for a new method of determination of
magnetic characteristics of the material in SPSM. With all the existing techniques such as
Epstein and single sheet tester being destructive and invasive, a non-invasive and non-destructive
technique has been proposed for the determination of the magnetic characteristics of material in
SPSM. This technique is simple and easy and requires FE simulations to perform the above task.
Modeling of electrical machines in Ansys Maxwell
This thesis provides detailed parameters and steps involved in modeling of SPSM under different
conditions such as motor, generator and open circuit test. Also the methods to perform
magnetostatic and transient simulation methods have been discussed.
Ampere turn distribution technique
A novel technique called ampere turn distribution technique has been developed. Here simple
calculations on magnetic field intensity and magnetic flux density combined with finite element
simulations have been used to determine the magnetic material used in SPSM. This technique
has been based on the hypothesis that the distribution of magnetic field intensity across different
parts of the SPSM is identical.
108
Validation of the ampere turn distribution scheme
Detailed experiments have been on SPSM as a motor, generator at different field currents and
load conditions and they have been compared with the newly determined magnetic material
determined from the AT distribution scheme to validate the new scheme
5.4 Future Scope
This research work presents a few challenges and opportunities for improvement and also
methods of using this scheme for other electrical machines
Improvement of calculation of magnetic field strength (H)
One of the disadvantages of the ampere turn distribution scheme is the difficulty in the
determination of magnetic flux density (B) accurately especially at higher field intensities (H). If
a suitable scheme or method can be determined to estimate the H accurately, the accuracy of this
scheme will improve. One of the methods to achieve higher accuracy in the determination of H is
to zoom in as closely as possible using the modify attributes tab in Ansys Maxwell and also
segregating the different parts of the SPSM as accurately as possible. This will result in better
determination of H and hence better results for the ampere turn distribution scheme.
Extension of the ampere turn scheme to other Electrical machines
The ampere turn distribution scheme has been presented for SPSM. The idea of H required to
setup B in different parts of SPSM being proportional irrespective of the material in the SPSM
can be extended to other electrical machines such as round rotor synchronous machines and slip
ring induction machines. These machines are widely used in the wind power generation and
therefore this scheme will be useful in the determining the magnetic characteristics of the
material in slip ring induction motors as well.
109
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112
Appendix
Figure A1 - SPSM wiring diagram
113
Figure A2 - SPSM datasheet
114