DEVELOPMENT OF SALIENT POLE ROTOR FOR CONVENTIONAL AUTOMOTIVE
AND AIRCRAFT ALTERNATOR TO INCREASE RELIABILITY
A Thesis by
Saurav Man Singh Basnet
Bachelor’s of Engineering, Kathmandu University, 2004
Submitted to the Department of Electrical and Computer Engineering and the faculty of the Graduate School of
Wichita State University in partial fulfillment of the requirements for the degree of
Master of Science
December 2007

© Copyright of 2007 by Saurav Man Singh Basnet
All Rights Reserved

DEVELOPMENT OF SALIENT POLE ROTOR FOR CONVENTIONAL AUTOMOTIVE
AND AIRCRAFT ALTERNATOR TO INCREASE RELIABILITY
The following faculty members have examined the final copy of this thesis for form and content, and recommend that it be accepted in partial fulfillment of the requirement for the degree of Master of Science with a major in Electrical Engineering
_________________________________
Ward T. Jewell, Committee Chair
_________________________________
John Watkins, Committee Member
_________________________________
Janet Twomey, Committee Member iii

DEDICATION
To my parents iv

Life is beautiful v

ACKNOWLEDGEMENTS
The author is obliged to the following people, without whom this project would not have been accomplished:
• Advisor Dr. Ward Jewell, whose interest, commitment, knowledge, motivation, wisdom, and inspiration are key factors in the accomplishment of this project.
• Ranjan Sharma, Pramod Ghimire, and Dr. Peter Freere, who showed the path of the research field and are always there for any kind of support.
• Robby Starr and Ghanashyam Shrestha, whose willingness to help and technical support was always of immense help.
• Larry Morton, without whom the mechanical construction involved in this thesis could not have been completed. His enthusiasm, experience, and high level of skill were always beneficial.
• The Department of Industrial Engineering at Wichita State University which provided the laboratory to construct the salient pole rotor.
• Dr. John Watkins, whose technical support was valuable.
• Dipti Regmi, Prabodh Bhusal, Chandika Dahal, Tejashwee Bhandari, Pukar
Mahat, Arvinthan Visvakumar, Tooran Emami, Miaolei Shao, Piyasak Poonpun,
Neelu Bijukchhe, and Vikash Bhatta, whose responses were always constructive. vi

ABSTRACT
This thesis includes the redesign and construction details of a salient pole rotor for an existing aircraft alternator. Salient pole rotor was designed to increase reliability of the conventional automotive and aircraft alternator. Details of the mechanical and electrical design methodology and implementation are included. Various parameters considered for design are also explained.
The designed rotor matches the dimensions of the conventional automotive and aircraft alternator rotor, since the same alternator stator was used. The stator had a three phase delta-connected winding. It is used in aircraft to charge a battery at various modes of operation, as explained here.
The experimental results of conventional automotive and aircraft alternator rotors and the salient pole rotor are compared and discussed. The salient pole rotor experiment included various air gaps and different field-winding tests. The rotor design is not exactly as required, but a thorough understanding of different aspects of the machine was achieved. Guidelines for further modifications are included in this thesis. vii

5
3.
3.
2.
TABLE OF CONTENTS
Chapter
1.
Page
INTRODUCTION .................................................................................................. 1
THEORY .............................................................................................................. 6
2.1 Direct Axis and Quadurature Axis.............................................................. 6
2.2 Equivalent Circuit ....................................................................................... 8
2.3 Power Angle Characteristics...................................................................... 9
DESIGN PARAMETERS .................................................................................... 11
3.1 Air Gap..................................................................................................... 11
3.2 Flux Density ........................................................................................... 12
3.3
3.4
Stator and Field Winding.......................................................................... 12
Wave Form .............................................................................................. 13
3.5 Reactance ........................................................................................... 13
ROTOR DESIGN................................................................................................ 15
4.1 Mechanical............................................................................................... 15
4.1.1 Field Winding ................................................................................ 18
4.2
4.1.2 Rotor Material................................................................................ 19
4.1.3 Insulation....................................................................................... 20
Electrical .................................................................................................. 20
4.2.1 Voltage Calculation ....................................................................... 21
4.2.2 Flux Calculation............................................................................. 22
4.2.3 Calculating Current ....................................................................... 22
4.2.3.1 Magnetizing Force ........................................................... 22
4.2.3.2 Magnetomotive Force ...................................................... 24
4.3 Approximating Size of Rotor Winding Surface ......................................... 27
4.3.1 Calculation of New Rotor Based on Previous Design ................... 28
EXPERIMENT .................................................................................................... 31
5.1 Experimental Setup I................................................................................ 31
5.1.1 Flux Measurement ........................................................................ 32
5.2 Experiment Setup II ................................................................................. 34
5.2.1 No Load Test................................................................................. 34
5.2.2 Short Circuit Test .......................................................................... 36
5.2.3 Synchronous Reactance ............................................................... 37
5.2.4 Estimating Number of Turns of Salient Pole Rotor........................ 38 viii

TABLE OF CONTENTS (continued)
Chapter Page
5.3 Experiment Setup III ................................................................................ 40
5.3.1 No-Load and Short-Circuit Test..................................................... 41
5.3.2 Synchronous Reactance ............................................................... 42
6.
7.
CONCLUSIONS ................................................................................................. 44
FUTURE RESEARCH ........................................................................................ 45
REFERENCES.............................................................................................................. 47
APPENDICES
A.
B.
Cross-Sectional View of Claw Pole Alternator ......................................... 51
Brief Description of Power Angle ............................................................. 52
C. Construction of Four-Pole Salient Pole Rotor .......................................... 55
D. Technical Information of Glass Tape ....................................................... 57
E. Calculating Pitch Factor and Distribution Factor ...................................... 59
F. Different Views of Rotor Layout 1 and 2 .................................................. 64
G. Excel Spreadsheet of Data Measured ..................................................... 66 ix

2.
3.
4.
LIST OF TABLES
Table
1.
Page
Calculating Length of Wire Required for 50 turns ............................................... 28
Calculating New Rotor Winding Surface............................................................. 29
Flux Measurement at Salient Pole Rotor ............................................................ 32
Flux Measurement at Salient Pole with Additional Series Resistance ................ 33 x

3.
4.
5.
LIST OF FIGURES
1.
2.
Figure Page
Twelve-pole claw pole rotor .................................................................................. 2
Basic functional block diagram of aircraft alternator ............................................. 3
Basic operation of alternator................................................................................. 3
Taxi mode............................................................................................................. 5
Claw pole performance characteristics................................................................. 5
6.
7.
Salient pole rotor (four-pole rotor)......................................................................... 6
Air gap flux............................................................................................................ 7
8.
9.
Salient pole synchronous generator phase diagram............................................. 8
Equivalent circuit diagram of salient pole rotor ..................................................... 9
10. Power angle characteristics.................................................................................. 9
11. Torque power angle characteristics.................................................................... 10
12. Torque angle characteristics at various field currents......................................... 10
13. Maximum flux density at center of pole .............................................................. 11
14. Flux pulling ......................................................................................................... 13
15. Phasor diagram .................................................................................................. 14
16. Dimension of original rotor.................................................................................. 15
17. Types of salient pole........................................................................................... 16
18. Salient pole rotor layout 1................................................................................... 18
19. Winding configuration of salient pole .................................................................. 18
20. Iron magnetization curve .................................................................................... 19
21. Insulating rotor winding surface with glass tape ................................................. 20 xi

LIST OF FIGURES (continued)
Figure Page
22. Three-phase rectifier .......................................................................................... 21
23. B-H characteristics plot....................................................................................... 24
24. Magnetic circuit................................................................................................... 24
25. Dimension of winding surface of rotor layout 1 ................................................... 28
26. New winding surface ......................................................................................... 29
27. Salient pole rotor layout 2................................................................................... 30
28. Flux measurement setup .................................................................................... 32
29. Measurement of flux at pole face........................................................................ 32
30. Extrapolated flux calculation ............................................................................... 33
31. Experiment setup for OC and SC test ................................................................ 34
32. Open-circuit test ................................................................................................. 35
33. Open-circuit test of claw pole rotor ..................................................................... 35
34. Claw-pole alternator voltage wave form ............................................................. 36
35. Short-circuit test.................................................................................................. 36
36. Short-circuit test of claw pole rotor ..................................................................... 37
37. Claw pole alternator current waveform ............................................................... 37
38. Corresponding armature current at rated voltage ............................................... 38
39. Extrapolated turns .............................................................................................. 39
40. OCC and SC test of 400 turns ............................................................................ 39
41. Sticking pole shoe on rotor pole ......................................................................... 40
42. OCC test for salient pole with pole shoe............................................................. 41 xii

LIST OF FIGURES (continued)
Figure Page
43. SC test for salient pole with pole shoe................................................................ 41
44. Salient pole waveform ........................................................................................ 42
45. Corresponding armature current at rated voltage of salient pole ........................ 43 xiii

AC
ACU
AWG
CO
DC
EMF
MFG
MMF
OCC
PWM
RPM
RPS
SC
SN
VR
LIST OF ABBREVIATIONS
Alternating Current
Alternator Control Unit
American Wire Gauge
Corporation
Direct Current
Electromagnetic Force
Manufacturing
Magneto-motive force
Open Circuit Saturation Characteristics
Pulse Width Modulation
Revolution Per Minute
Revolution Per Second
Short Circuit
Serial Number
Voltage Regulator xiv

Percentage
LIST OF SYMBOLS
°
%
φ
δ w s
π n s
τ
L
H
µ
ο
ω
A
AT
Ω
V
Degree
Magnetic Flux
Power Angle
Angular Velocity
Pi
Speed in Revolutions per Minute
Pole Pitch
Length
Henry
Permeability of Free Space
Angular Frequency
Ampere Turns
Ohm
Voltage
Ampere xv

CHAPTER 1
INTRODUCTION
This project dealt with redesigning the conventional automotive and aircraft alternator. Aircraft companies are looking for more efficient alternators at low revolutions per minute (RPM), which was the main design goal of this project. The main parameters usually considered for redesign are the rotor and stator. The rotor was considered for this thesis, because it seemed simpler than redesigning the stator. Moreover, designing a new stator might change the complete alternator structure, while a new rotor could be limited to the existing rotor dimensions.
The basic application of conventional automotive and aircraft alternators should be known before redesigning them. The aircraft alternator (claw pole) rated at 24 volts
(V), 60 ampere (A) was used in this thesis. The name claw pole is derived from the rotor structure as shown in Figure 1. Generally alternators are designed with 12 or 16 poles, considering the tradeoff between machine efficiency and magnetic leakage (a low number of poles causes low efficiency, and a high number of poles causes higher magnetic leakage). As shown in Figure 1, two oppositely poled claw halves interlock together to form a 12-pole rotor with alternate north-south fingers attached to the shaft.
The spool is a round-shaped non-metallic bobbin also attached to the same shaft and sandwiched between oppositely poled claw halves consisting of 950 turns of 23
American wire gauge (AWG) winding wire. The ends of the field winding are connected to the respective slip rings for the direct current (DC) excitation. The pulley for the belt drive is connected at the left end of the rotor shaft (in reference to Figure 1). The alternator is designed to operate within the range of 2,000 to 10,000 RPM.
1

Finger
Shaft
Spool
Figure 1: Twelve-pole claw pole rotor [1].
When the rotor rotates, the magnetic flux that is produced cuts the stationary three phase stator winding, thus generating the required alternating current (AC) output.
The stator consists of 84 turns of 17 AWG wire. The generated three-phase output is then fed to the inbuilt rectifier diodes, which then charge the 24 V battery. A complete alternator structure is shown in Appendix A [1].
The alternator is used to do the following:
1. Charge the 24 V battery.
2. Even during the faulty conditions, sustain the critical load for flaps, wind strobe, tail-beacon, navigation light, landing gear, fuel pump, avionics, and instruments.
3. Keep the alternator rating from exceeding 80 percent, even if all the loads are operating at the same time (operating at full load).
Figure 2 shows the basic functional structure of the conventional automotive and aircraft alternator. An alternator control unit (ACU) maintains the required DC voltage of the alternator field, which is denoted by F. It also acts as an interface between the loads and the alternator. Maintains the good regulation in the system, like in case of fault detection or when main battery fails, it brings the extra (emergency) battery into action.
2

Alternator
B
F
Control
Regulation
Fault Detection
Control
Avionics
Battery
Lighting
Flight Controls
Engine
Display
Loads
Fault Control
ACU
Figure 2: Basic functional block diagram of the aircraft alternator action.
As shown in Figure 3, the voltage regulator (VR) maintains the current supplied to the field. It senses the battery-charging voltage and interrupts the current to the field when voltage reaches above the required limit (depending on type of battery used, in this case 28 V).
28
1
VR Alternator w
Voltage (V)
2
Fuse
Load
Battery
3
Time (s)
Figure 3: Basic operation of alternator.
When the charging voltage falls below the limit, current is again supplied to the field. In this way, the rotor receives a pulsed DC current. Another way to sense the load current and use pulse width modulation (PWM) as a feedback mechanism is to control the
3

stator current. This provides constant output voltage regardless of the load applied.
PWM is economic and robust since it uses solid-state devices. The-duty cycle varies according to the load condition. Three important cases in Figure 3 are mentioned below:
1. At the initial state, the motor starts with no load condition, which operates at minimum duty cycle at no load.
2. As the load increases the duty cycle also increases.
3. The maximum given condition is called a full field. If it exceeds beyond a full field, then the voltage sags at a given RPM.
To charge a 24 V battery, the alternator should supply at least 27.6 V constantly, which is specified for the battery [1]. The charging voltage should be kept below 28 V to prevent the battery from overcharging, which is the reason behind choosing 28 V PWM.
The fuse is rated at 5 A. The batteries used are capable of running critical loads for about 30 minutes.
Alternator load varies according to the mode of an aircraft. It is at minimum load in taxi mode and maximum load when taking off and landing. While an aircraft is at flying mode, the alternator experiences a normal load. Since this project concerns increasing the current at low RPM, the taxi mode is highly considered. Figure 4 shows an aircraft exiting the hanger and going towards the runway, or taxi mode.
This project dealt with designing a new rotor that could uplift the lower edge of the claw pole characteristics, as shown in Figure 5, where even at 2,600 RPM, the current is about 4 A [2]. This does not mean that output at higher RPM was not considered. The aim was that the new design should produce optimum output at high speed also.
4

M
O
D
E
T
A
X
I W
A
Y
R
U
N
Figure 4: Taxi mode.
70
60
50
40
30
20
10
0
0 2000 4000 6000
Speed(RPM)
8000 10000
Figure 5: Claw pole performance characteristics [2].
A salient pole machine is used when high current at low RPM is needed.
Comparatively, salient pole machines are easy to design and construct. Therefore, the salient pole rotor was considered for the design. Chapter 2 discusses the theoretical aspect of the salient pole machine.
5

CHAPTER 2
THEORY
This section describes the theoretical overview of a salient pole alternator. As mentioned earlier, the salient pole machine is used for lower-speed applications and is very popular in large vehicles with a high-current requirement. Unlike a cylindrical rotor, the salient pole rotor has distinguished varying air gaps as shown in Figure 6. The difference in air gaps create different inductance in the stator winding and change in the flux linkage. The study of this type of machine is divided into two parts, namely the direct axis and the quadrature axis. The axis in line with the pole is the direct axis, where permeance is high, and the axis in line with the interpole is called quadrature axis, where the air gap is high and permeance seen by the stator is less. The size, number, and shape of the rotor pole may vary, depending upon design constraints [3,
4].
Figure 6: Salient pole rotor (four-pole rotor) [4].
2.1 Direct Axis and Quadurature Axis
The direct and quadurature axes could be easily determined by locating the generated voltage
6

φ ar
is directly opposite to the field pole and opposite to the direction of field flux. On the other hand in Figure 7 (b), φ ar lagging ° φ ar lags the field flux by 90 + φ lag
, where φ lag
is the angle by which the armature current in the direction of generated voltage lags the generated voltage. If φ lag
is 90 , then φ ar
appears in the direct axis region, and when
φ lag
is zero, φ ar appears in the interpolar region. The armature reaction flux φ ar
is higher when directly opposite to the field poles and lower when in quadrature to the field poles.
Field pole Field pole
Φ f
I a
Φ f
Φ f
Φ f
Φ ar
E af
Φ ar
N
Armature
S
Φ ar
E af
I a
Φ ar
N
Armature
S
(a) Direct axis (b) Quadrature axis
Figure 7: Air gap flux.
The armature current can be partly named as direct components; φ ad
along the axis of the poles whereas
φ aq
along the interpoles. The armature reaction flux φ ar
is the vector sum of direct axis and quadrature axis flux, and the resultant air gap flux is the sum of
f
and φ ar
, as shown in Figure 8 [5].
7

Φ ar
Φ aq
Φ ad
I q E af
Φ r
I d
I a
Φ f
Figure 8: Salient pole synchronous generator phasor diagram.
2.2 Equivalent Circuit
The equivalent circuit diagram of the direct axis (d-axis) and quadrature axis (qaxis) of salient pole machine are shown in Figure 9. Total impedance of the direct axis is given by the armature reactance in series with field and parallel with direct axis reactance, whereas in the quadrature axis, the voltage induced by one side of the coil is canceled by the voltage induced in the other side; therefore the field has no effect [6].
(a) Direct axis (b) Qudrature axis
Figure 9: Equivalent circuit diagram of salient pole machine.
8

2.3 Power Angle Characteristics
The non-uniform air gap of salient pole machines creates a difference in magnetic reluctance. This is low along the direct axis and high along the quadrature axis. When the stator flux is aligned with direct axis armature reaction reactance, the stator current is which is experienced when stator flux is parallel to the quadrature axis. The change in armature reaction reactance with a power angle is shown in Figure 10 [7]. A brief description of power angle is given in Appendix B.
π / 2
π
Figure 10: Power angle characteristics.
Unlike a cylindrical pole machine, a salient pole machine develops two different types of torque, as shown in Figure 11 [7]:
1. Reluctance Torque: The torque experienced by an unexcited pole as the power angle varies. This torque changes according to the equation (1). m
T = w s
V 2
2
1
X q
1
−
X d sin2 δ (1)
9

2. Resultant Torque: The torque experienced by an excited pole as the power angle varies, which is the sum of electromagnetic torque and reluctance torque as shown in equation (2). m
T = w s
VE f
X s m sin δ + w s
V 2
2
1
X q
1
−
X d sin2 δ = T m
+ T r
(2)
Figure 11: Torque power angle characteristics.
Figure 12 shows the torque angle characteristics at different excitation currents with constant terminal voltage. Here I f1
>I f2
>I f3
>I f,
signifies that even at the zero field current, the reluctance torque keeps the salient pole machine in synchronism.
Figure 12: Torque angle characteristics at various field currents
10

CHAPTER 3
DESIGN PARAMETERS
Magnetic loading and electrical loading of the machine varies with the frame size.
The flux density on the air gap determines magnetic loading. Figure 13 shows that the flux density is maximum at the center of the pole. Since the salient pole rotor is either machined from solid iron or punched out of iron plates, the maximum flux achieved is determined by the saturation level of the iron. Different electromagnetic materials have their own saturation levels. Selection of material depends on the design requirements.
3.1 Air Gap
Figure 13: Maximum flux density at center of the pole.
The trend is to make the air gap as small as possible. Actually the air gap length is chosen such that the machine runs satisfactorily under normal operation and faulty conditions. The air gap length should be a tradeoff between total field and mechanical difficulties [6].
3.2 Flux Density
Flux density determines the optimum magnetic design of the machine. If the rotor iron saturates at 1.2 Tesla, the designed air gap flux should be more than 80 percent of
11

the saturation level for optimum magnetic design. Air gap flux depends upon the winding wires and type of rotor material.
3.3 Stator and Field Winding
Stator winding is where the actual voltage is generated. Wire is wound around the laminated punched slots. Different types of wire can be used. For a small machine below 1,000 V, round wire is usually preferred. The field winding is responsible for magnetomotive force (MMF) generation. In the salient pole, the arrangement depends upon the size and speed of the machine.
Winding should fulfill the following minimum requirements [6].
1. The number of turns should be accurate enough to generate the required voltage at appropriate flux.
2. The conductor should have correct AWG or cross section to withstand the load current.
3. The conductor should withstand the limited temperature rise.
4. The conductor should be insulated from the core and between turns, which should withstand surge voltages.
5. The conductor should withstand the electro-magnetic forces caused during normal switching, faults and out-of-phase switching.
6. The conductor should withstand the centrifugal force in high-speed generators.
3.4 Waveform
Sinusoidal voltage output wave form is always preferred. Considerable distortion in the system adds undesirable harmonics and the waveform is distorted. Loads contribute to more distortion due to flux pulling, as shown in Figure 14, and non linearity.
12

During flux pulling, the flux is pulled towards the higher reluctance path, .i.e., away from the center to the edge. Non-linearity is due to variation in impedance.
Figure 14: Flux pulling.
The waveform could be improved by changing the shape of the pole face, maintaining the minimum air gap at the center of the face, and increasing the gap as it moves away from the center. The usual practice is to maintain 1.5 to 2 times higher air gap at the edge of the pole face than at the center. This reduces the flux pulling effect, thereby decreasing noise.
3.5 Reactance
Different types of reactance occur in the process. Armature and synchronous reactance are discussed here. Armature reactance is denoted by armature reaction. As shown in Figure 15, reactance perpendicular to the load current I. Synchronous reactance is denoted by. is the sum of leakage reactance X
1
and armature reactance
13

θ θ
(a) Armature reactance (b) Synchronous reactance
Figure 15: Phasor diagram.
The value of
X means that the field excitation increment is less than the machine with a high s
X s from no load to a rated load [6].
14

CHAPTER 4
ROTOR DESIGN
This chapter explains the mechanical and electrical design of the new rotor. The mechanical design explains the dimensions, layout of the rotor, and the parameters considered. The electrical design mainly focuses on the voltage and current calculation with appropriate rotor winding.
4.1 Mechanical Design
A new rotor was designed to fit the claw pole alternator frame. Therefore, the dimensions should match the original rotor. Figure 16 shows the dimensions of the original rotor. Since the design was limited to original rotor, the length and diameter were known variables, and the diameter was determined by the peripheral speed, as shown in equation (3). The rotor should withstand the centrifugal force under runway speed (when the system is suddenly unloaded when operating at rated load) [8].
5 cm
Figure 16: Dimension of original rotor. peripheral speed = Π dn s

 m s


(3)
15

where d = rotor diameter in meter
The alternator was rated at 166.66 revolutions per second (RPS). With a diameter of 0.093 meter, then the peripheral speed will be 49 ms
-1
. Usually, if the peripheral speed is less than 50 ms
-1
, the rotor poles are screwed to the rotor body.
Since rotors experience very high-speed poles, they are designed to be constructed form a single piece of iron.
Two types of poles are used in the salient pole machine: a round pole and a rectangular pole, as shown in Figure 17.
B
L
(a) Round pole
B
L
(b) Rectangular pole
Figure 17: Types of salient poles.
The shape of the pole is determined by the pole pitch denoted by τ , or
τ =
π d
( m ) p
(4) where d = rotor diameter in meter p = number of poles
16

In the round pole, the ratio of width (B) and pole pitch should be 0.6 to 0.7. For the round pole, the length (L) is equal to the width of the rotor. Therefore, the ratio to 0.7. In the rectangular pole, the ratio of the rotor length and pole pitch should be 1 to
5. The ratio is maintained below 3 for an economical field design. The ratio
[8].
A new rotor was designed for high-speed operation; therefore, even a lower number of poles can generate the same voltage level as compared to low-speed operation with a greater number of poles. A four-pole rotor is suitable for the design.
The reasons for choosing a four-pole rotor are as follows:
1. It can fit sufficient winding wires.
2. It makes construction simpler.
3. Easy to wind wires.
4. High number of pole increase iron loss
From equation (4), for a four-pole rotor, τ is 0.073 m and that a round pole is suitable. As shown in Figure 17, for a round pole, the width of the pole shoe is equal to the length of the pole shoe, and there will be much less space available between the poles. This makes hand winding around the poles difficult.
Therefore, it is not possible to design a complete round pole rotor. Changes have been made to meet the design constraints.
Figure 18 shows the designed four-pole salient pole rotor layout 1. CATIA V5R17 engineering drawing software was used to design the layouts. The construction procedure is described in Appendix C
17

Figure 18: Salient pole rotor layout 1.
4.1.1 Field Winding
The salient pole rotor was constructed in such a way that field windings could be wound around the field poles . Alternate north and south poles were maintained by winding clockwise and anti-clockwise in alternate poles, as shown in Figure 19, and the two ends of the wire were connected to slip rings for the DC supply. The slip rings were attached to the rotor shaft, and the current was passed through the carbon brushes, sliding on the slip rings.
(a) Front view
Wire end
(b) Side view
Figure 19: Winding configuration of salient pole.
18

4.1.2 Rotor Material
To produce as much flux as possible for a given value of field intensity (H), the material should not be saturated. An increase in the current does not increase the flux after saturation is reached, as shown in Figure 20. Under any circumstances, the maximum flux that cast steel can produce is 1.2 Tesla. N and I in equation (5) can be varied according to the need but cannot take flux density above the saturation limit.
Figure 20: Iron magnetization curve.
B =
NI µ
ο airgap
( Tesla ) where
N = number of field winding turns
I= field current
µ
ο
= 4 π × 10
− 7 airgap = gap between field winding and armature winding
(5)
19

Cast steel was chosen for the design, since it has comparatively higher flux density at saturation than cast iron and is easily available in the market .
4.1.3 Insulation
The rotor material and field winding should be properly insulated. Insulating material should protect it from short circuits, temperature rise, moisture, etc. Basic properties needed in insulating material are mentioned below [3].
1. Good thermal conductivity.
2. High degree of thermal stability.
3. High resistivity or specific resistance.
4. Low dielectric hysteresis.
5. High dielectric strength.
Scotch brand No. 316 glass cloth tape was used for insulating the rotor. It is manufactured by Minnesota Mining and MFG. Co. Its technical data is mentioned in
Appendix D. Figure 21 shows the insulated rotor.
Figure 21: Insulating rotor winding surface with glass tape.
20

4.2 Electrical Design
The aim of the electrical design was to find an appropriate number of turns with suitable AWG for a four-pole salient pole rotor to produce the required output.
4.2.1 Voltage Calculation
The rectified output voltage for a single engine aircraft alternator is around 28 V.
Therefore 28 V is considered for the design. Figure 22 shows the rectification of a three- phase AC source. The rectifier is the electrical device that converts alternating current to direct current.
Figure 22: Three-phase rectifier.
The average no-load DC voltage of the three-phase rectifier can be written as equation
(6).
V dc
=
1
π
3
π
6
− π
6
2 V
LL cos ω td ( ω t)
=
1
π
3
× 2 V
LL
[ sin ω t
] π
−
6
π
6
=
1
π
3
× 2 V
LL
[ sin
( )
6
− sin
(
−
π
6
) ]
=
3
π
2
V
LL
(6)
21

Assume V = 28 V dc
That is V
LL
= 20.73 V
The acquired V
LL
is used to calculate the flux.
4.2.2 Flux Calculation
The average voltage generated by a single turn can be written as equation (7).
φ
E = t


 volt turn


(7)
Equation (7) needs some modification for sine-wave application. Moreover the frequency needs consideration while designing the generator. Also, a single turn is no longer convenient when many turns are used for winding, denoted by N
P
, where N
P
is the number of turns per phase [6].
E ' = 4.44N
p
f (8)
The generated voltage is always less than E’, since it does not include factors affecting voltage generation. The most common factors have been included in equation
(9).
E = 4.44Np
φ fK p
K d
(9) where K
P
and K d
are pitch factor and distribution factor, respectively. These factors depend upon the stator winding configuration. The calculation technique is described in
Appendix E.
4.2.3 Calculating Current
The flux calculated from equation (9) is used to find the field current. The sections below describe how this is achieved .
22

4.2.3.1 Magnetizing Force
Magnetizing force, also called magnetic field strength, is defined as the magneto motive force per unit length at a given point in any magnetic circuit or per unit length of path, or
F
H = (Lenz )
L
(10) where
H = magnetizing force
L = length of path in cm
The magnetizing force can also be explained as the product of flux density and the inverse of the permeability, as shown in equation (11).
H =
B
µ
⇒
B
H
= µ = 4 π × 10
− 7
(11) where
µ = absolute permeability of free space
B = flux density in Tesla ( Wb m 2 )
Here flux density is calculated from flux and area of the pole face, which is given by equation (12).
φ
B = (
A
Wb m
2
) (12)
As shown in Figure 23, the value of µ at any point is given by the value of B divided by H at that point. The point at which the tangent cuts the B-H curve is the maximum permeability [9]. In non-magnetic material, µ is constant, which gives the liner
B-H relation.
23

Figure 23: B-H characteristics plot.
4.2.3.2 Magnetomotive Force
Magnetomotive force (MMF) is any physical cause that produces magnetic flux
[9]. It is also called the magnetic potential, a property of certain substance that gives rise to a magnetic field [10]. It is also defined as the strength of the magnetic field in a coil of wire, which depends on the magnitude of the current flowing in the turns of the wire, whereas the lines of force depend upon the turns of the wire [11]. The standard unit of the MMF force is ampere turns (AT), which is one ampere of direct electric current flowing in the single turn of a coil in a vacuum. It is sometimes represented as
Gilbert (G).
F =
N r
× I
0.796
, G = N r
× I ( AT )
or,
F
I = ( A )
N r
(13) where,
F = magnetomotive force in ampere turns
I = current in amperes (A), direction as shown in Figure 24
N r
= field winding turns per pole
24

Figure 24: Magnetic circuit.
I, calculated from equation (13) is a field current. It is clearly seen that field current depends on many factors, some of them are mentioned below.
DC Excitation Voltage
The alternator is separately excited via a normal DC power supply or semi-conductor devices. DC excitation is supplied to the rotating field through the slip rings and the brushes. At constant speed, amount of electromagnetic force (EMF) generated depends upon DC excitation.
Alternator Speed
Alternator speed depends on the prime mover. Generated voltage varies with speed, and usually the alternator is rated at maximum speed.
E = B l v
( )
(14) where
B = flux density in Tesla l = axial length of the rotor in meter v = velocity of the rotor in meter sec
25

Armature Winding Turns and AWG
The armature winding is the main current carrying winding where the electromotive force generated by magnetic flux rotation is induced. The current carrying capacity depends on the size of the winding; generally, lower AWG wires are used.
Winding turns depend on the desired output.
Winding Factor
Pitch factor and distribution factor together are called the winding factor, denoted by k w
. This factor is introduced to balance the difference in the phasor sum and the numerical sum (phasor sum is less than numerical sum) of the phase winding when connected in series. k w ranges from 0.85 to 0.95 for most of the three-phase winding.
Air-gap
The length of the air gap has an immense effect on the machine performance. It reduces the effect of armature reaction by creating large reluctance to the path of flux produced by the armature MMF. Some limitations caused by a large air gap are mentioned as follows [8]:
• Small value of intrinsic regulation.
• Higher value of stability limit
• Higher synchronizing power makes machine less sensitive to load variation.
On the other hand a larger air gap produces low noise, better cooling, and lower unbalanced magnetic pulling. The preferred way to choose an air gap in a salient pole machine is length of air gap divided by pole pitch, which should be 0.01 to 0.015, where the length of the air gap is measured at the center of the poles.
26

Rotor Winding Surface
The rotor winding surface is the space allocated for wires to wind around. Size and shape of the surface depends on the numbers of turns required and the rated speed of the alternator. It is always designed to fit extra turns.
Field Winding Turns and AWG
The electric coil around the rotor pole is responsible for producing the magneto- motive force to set up a flux in the electric machine. The number of turns and AWG depends upon the flux requirement of the alternator. AWG also depends upon the current requirement; the higher the current, the lower the AWG.
Packing factor
The packing factor is dimensionless and always less than unity, or packing factor = number of turns in a one layer × volume of volume of winding surface wire
(15)
4.3 Approximating Size of Rotor Winding Surface
This section explains the technique used to approximate the new winding surface dimension compared to the result of the existing winding surface (dimension of rotor layout 1). Figure 25 shows the dimensions of an existing winding surface, which cannot fit more than two layers of winding. A greater number of turns was required to achieve design goals. The calculation in Table 1 is for 50 turns, in order to fit the rotor inside the machine, the winding space should be increased, i.e., the size of the winding surface needs to be decreased.
27

Figure 25: Dimension of winding surface of rotor layout 1.
TABLE 1
CALCULATING LENGTH OF WIRE REQUIRED FOR 50 TURNS
One turn around the winding surface 2*2*4.5*4.5=13.5 cm
50 turns around the winding surface
Simplifying the calculation
13.5 * 50=650 cm
Choose 700 cm = 7 m (approx.)
4.3.1 Calculation of New Rotor Based on Previous Design
At most, the design requires 300 turns per pole, which is six times more than the previous design. Calculating the new winding surface, based on Figure 25, is shown in
Table 2. This determines the shape and size of the winding surface to fit the estimated number of turns. It estimates the length of wire, which is always beneficial when purchasing wire.
28

TABLE 2
CALCULATING NEW ROTOR WINDING SURFACE
New length of wire 7*6= 42 m
Height of winding surface 0.02 m
Diameter of 24 AWG wire 0.00051 m
Number of turns could be adjusted per layer 0.02/0.00051=39..21
≈ 39
For 0.5 packing factor
Numbers of layers needed
39*0.5=19.5 ≈ 19
300/19=15.38 ≈ 16 layers
Winding surface reduction at each ends 16 * 0.00051=0.00816 m
To provide more room for winding, 1cm was decreased on both sides of the winding surface, as shown in Figure 26.
Figure 26: New winding surface.
Figure 27 shows rotor layout 2 with the new winding surface. See Appendix F for front and side views of this rotor.
29

Figure 27: Rotor layout 2.
30

CHAPTER 5
EXPERIMENTS
This section explains the different tests preformed results, and discussions. A
± 5 − 10 percentage tolerance was expected in the results obtained. Due to the unavailability of odd numbers of wire sizes, 24 AWG wire was used instead of 23 AWG.
Experiments were performed at Wichita State University in the Electric Machine
Laboratory .
5.1 Experimental Setup I
A Leader LPS-151 DC tracking power supply was used to supply 2 V DC voltage directly to the field winding, as shown in Figure 28, which was manufactured by Leader
Electric Corporation, Japan. Omega Engineering Gauss/Teslameter model HHG-22 was used to measure the flux generated. A power resistor, Decade box model number 240-
C manufactured by Clarostat Manufacturing Company, Inc., Dover NH was used to increase the field winding resistance.
Ends of the field winding were connected to the voltage source with resistance in a series. The purpose of series resistance is to maintain 13.6 Ω (resistance of claw pole field winding) to make the voltage and current ratio constant in both rotors. The tip of the Gauss/Teslameter sensor was placed on the rotor pole face to measure the flux, as shown in Figure 29. Alternate poles should give positive and negative values simultaneously, in order to have alternate north and south poles.
31

Figure 28: Flux measurement setup.
5.1.1 Flux Measurement
Figure 29: Measuring flux at pole face.
Calculating flux is a vital issue for any machine design. In this study a rough approach was considered in order to obtain a general idea about flux needed to generate 28 V. This may not hold true in practical situations. First, the claw pole rotor flux was measured to be 140 Gauss at 0.2 A with 13.6
Ω . Then the new rotor flux was measured with different numbers of field winding turns (Table 3). The current rating was different at the different number of turns, so these results may be misleading.
TABLE 3
FLUX MEASUREMENT AT SALIENT POLE ROTOR
Turns Flux ( Gauss) Current (A) Resistance ( Ω )
100 26.111 2 1
200 55.727 1.2 1.8
400 70 0.6 3.6
Again, series resistance was added in reference to claw pole, and 0.2 A was maintained in each experiment (Table 4). Then this data was extrapolated, as shown in
32

Figure 30, to determine the required number of turns to generate a required flux to produce 28 V. Results shows that more than 2,400 turns are required to generate 140
Gauss of flux, which is about 600 turns per pole. This was inadequate for the designed rotor, so more tests should be performed to verify this result. Moreover, the number of poles of the claw pole and new rotor were different. Therefore the same flux at each pole may not give the same voltage at the stator.
TABLE 4
FLUX MEASUREMENT AT SALIENT POLE WITH ADDITIONAL RESISTANCE
Turns Flux (Gauss)
100 1.587
200 7.581
160
140
120
100
80
60
40
20
0
0 500 1000 1500
Number of turns
2000 2500
Figure 30: Extrapolated flux calculation.
The following assumptions were made:
3000
1. The increment of flux with the number of turns is linear.
2. There is no rotor saturation.
33

5.2 Experimental Setup II
The alternator was driven by a three phase induction machine. The belt drive was adjusted so that the alternator rotated at 2,300 RPM. A CDT-2000 Digital
Tacometer, manufactured by Electromatic Equipment Company, Inc., was used to measure the RPM of the alternator. K-5325 multimeters, (S/N 1065158 and S/N
1042517), manufactured in Tawan, were used to measure DC voltage and current. An
XHR 100-10 DC power supply (S/N E00110037), manufactured by Xantrex Technology
Inc., Canada was used to supply field current and voltage and AC voltage and current were measured by a Fluke 434 three power quality analyzer (S/N DM8890031) manufactured by Fluke corporation, Holland. The experimental setup of the open-circuit
(OC) and short circuit (SC) test are shown in Figure 31.
The plotted values of the experiments are the peak values, so that they are directly comparable with DC values .
Figure 31: Experiment setup for OC and SC test.
5.2.1 No-Load Test
The no-load test, also called the open-circuit test was, performed at constant speed. Open-circuit voltage (V
OC
) was measured at varying field currents as shown in
Figure 32. An Open-circuit saturation curve was obtained plotting V
OC
as a function of field current. When the per-phase voltage was plotted against field current, it was
34

referred as open-circuit saturation characteristics or OCC. The air gap line shows the predicted values if the steel does not saturate. This characteristics curve is also called the magnetization curve, since the characteristic represents the iron and air gap geometry of the machine.
Field winding
I f
V ocd
Stator winding
V p
Figure 32: Open-circuit test.
Figure 33 (a) shows the OCC of the claw pole alternator at the AC side. The purpose of these tests was to generate a basic idea about new rotor behavior based on the original characteristics. Figure 33 (b) shows the OCC at the rectifier end. Both readings are similar because the capacitor at the rectifier end maintains the output voltage around the peak value. This is also called the smoothing capacitor or filter capacitor which smoothes raw (varying) output voltage from the bridge. In both cases,
28 V was achieved at 0.8 A field current.
70
60
50
40
30
20
10
0
0 0.2
0.4
0.6
0.8
Field current (Amps)
1
( a) AC side airgap line
OCC
1.2
1.4
25
20
15
10
5
0
50
45
40
35
30
0 airgap line
OCC
*
0.2
0.4
0.6
Field current (Amps)
(b) Rectifier end
0.8
1
Figure 33: Open-circuit test of claw pole alternator.
35

Figure 34 shows a 120 phase shift of the stator phases. Odd number harmonics predominant, since the wave form is not pure sinusoidal. Since the output is rectified, this does not have much effect.
Figure 34: Claw pole alternator voltage wave form.
5.2.2 Short-Circuit Test
The short-circuit test was performed to measure the short-circuit current or I
SC
.
The stator terminal of the machine was short through an ammeter Figure 35 shows the schematic diagram of the short-circuit test. The field current was increased up to 1.5 times the I rated
and the current was measured from the ammeter
Field winding
I f
I scd
Stator winding
I sca
Figure 35: Short-circuit test.
The short-circuit characteristics before and after the rectifier end of the claw pole alternator are shown in Figure 36. Both readings have almost the same value; therefore, later on, only output before the rectifier is considered. Current waveform which
36

is shown in Figure 37.
60
50
40
30
20
10
0
0 0.2
0.4
0.6
0.8
Filed current (Amps)
1
45
40
35
30
25
20
15
10
5
0
0 1.2
1.4
0.2
0.4
0.6
Field current(Amps)
(b) Rectifier end
0.8
(a) AC side
Figure 36: Short-circuit test of claw pole alternator.
1
Figure 37: Claw pole alternator current wave form.
5.2.3 Synchronous Reactance
The sum of armature reaction reactance and leakage reactance is called synchronous reactance. It is denoted by line through the origin, cutting the OCC at the rated voltage ( V rated
). The corresponding point on the SC current is the armature current (
V rated
and
Therefore, I should be multiplied by 3 . Also, in order to obtain synchronous reactance
37

in Ω , V rated
and is given by
X
S
=
V rated
I a
=
17.8
43
= 0.413
Ω
(16)
The saturated reactance voltage and current in the system. The value of number of rotor poles, rotor size, armature, and field winding, etc.
22
20
18
16
14
12
10
8
6
4
2
0
O
0 rated voltage
0.2
0.4
0.6
0.8
P armature current
1 1.2
1.4
50
40
30
20
10
0
90
80
70
60
OCC
SC
Field current, If
Figure 38: Corresponding armature current at rated voltage of claw pole.
5.2.4 Estimating Number of Turns for Salient Pole Rotor
No-load tests and short-circuit tests were performed on 100, 200, and 400 number of turns to extrapolate (to estimate the value of a variable outside the tabulated or observed range) the required number of turns and to achieve the design goals. Figure
39 show that to achieve 28 V, the number of turns should be around 1,600.
38

The following assumptions were made:
1. The increment of flux with the number of turns is linear
2. Neglect losses (windage loss, heat loss etc.)
20
15
10
5
35
30
25
0
0 500 1000 1500 2000
Number of turns
Figure 39: Extrapolated turns.
Although the estimation shows that adding turns increases the voltage, the opencircuit voltage with salient pole rotor is very much less compared to the claw pole rotor.
OCC and SC tests of the salient pole rotor with 400 turns are shown in Figure 40.
9
8
7
6
3
2
5
4
1
0
0
OCC
I sc
30
25
20
15
10
5
1 2 3 4 5
0
Field current (Amps)
Figure 40: OCC and SC test of 400 turns.
39

Several reasons for the lower open-circuit voltage may be are as follows:
1. Saturation of the rotor iron: This is unusual in this case because the OCC is still linear.
2. Fewer turns: As mentioned in equation (5), increasing the number of turns increases the flux density. The length of the rotor and velocity are constant in this case equation (17) for the OC and SC tests. Therefore, B directly affects the generated voltage.
E = Blv
=
NI µ
° airgap
× rotor length × velocity (17)
3. Air gap: as shown equation (17), the air gap inversely affects the generated voltage. It is always desired to have a minimum air gap. The salient pole alternator has about 0.7 mm air gap, which is still high compared to the 0.2 mm claw pole alternator. Therefore, the air gap could be reduced by adding a pole shoe .
5.3 Experimental Setup III
Experimental setup III is the same as setup II. This section explains the OCC and
SC tests with the addition of a pole shoe. As shown in Figure 41, 0.381 mm of Precision
Brand steel, UPC number 16530, was used for the pole shoe. Devcon plastic welder, number 14320, was used as the adhesive and plastics ties were used to hold it together. It is recommended to apply the ties for at least 24 hours before using it.
40

Figure 41: Addition of pole shoe on rotor pole.
5.3.1 No-Load and Short-Circuit Tests
Although decreasing the air gap increases the stray losses, this test was done to compare the results with the claw pole alternator. Figures 42 and 43 show the opencircuit voltage and short-circuit test before the rectifier. Reducing the air gap improved the voltage and current profiles, which is saturating at 2 A, therefore, it does not help increasing field current beyond that. The measured field winding resistance at 800 turns was 7.3
Ω , which is almost half the claw pole field winding resistance. Certainly a greater number of turns improve the profile but some other measure should be considered for better performance, which is explained in the recommendations for future work.
14
12
10
8
6
4
2
0
0
400 turns
200 turns
800 turns
1 2 3 4
Field current (Amps)
5 6
Figure 42: OCC test for salient pole with pole shoe.
41

30
25
20
15
10
5
0
0
400 turns
200 turns
800 turns
1 2 3 4
Field current (Amps)
5 6
Figure 43: SC test for salient pole with pole shoe.
The salient pole-open circuit waveform is shown in Figure 44 (a), which indicates that odd harmonics is predominant. Figure 44 (b) shows the short-circuit current wave form, which is distorted due to the uneven air gap caused by adding the pole shoe.
(a) OC voltage (b) SC current
Figure 44: Salient pole waveform.
5.3.2 Synchronous Reactance
This section compares the saturated synchronous reactance between the claw pole, as mentioned in Section II and the salient pole alternator. The saturated synchronous reactance of the salient pole with 800 field winding turns is shown in
Figure 45 and is calculated as:
42

X s
=
7.5
33
= 0.227
Ω
(18)
1
O
0
5
4
3
2
8
7
6
0 rated voltage
0.5
1 1.5
armature
2
P
2.5
10
0
70
60
50
40
30
20
Field current, If
OCC
SC
Figure 45: Corresponding armature current at rated voltage of salient pole.
Equation (18) shows that salient pole synchronous reactance saturates earlier than the claw pole. This may be the reason for low-voltage output of the salient pole.
The low value of no-load [6]. Though performance could be improved by increasing the armature or field winding turns, number of rotor poles, etc., synchronous reactance increases the copper loss. Therefore it should worth a risk of excessive copper loss.
43

CHAPTER 6
CONCLUSIONS
A salient pole rotor is developed to enhance the performance of automotive and aircraft alternator. The salient pole rotor replaces the original claw pole rotor. The rotor is designed to fit the existing stator.
The process began with the understanding of the use of generator in the aircraft system. Detailed theoretical design of the generator followed suit and the rotor construction work was commenced. Different tests have also been performed to verify the performance of the generator. Due to some technical constraints, the required goal is not fully achieved.
The power or the current form the generator is restricted by the flux linkage of the rotor and stator, major reasons being the air gap, while the voltage is as per required.
The static parameters such as no-load and sort circuit are experimentally deduced.
From the results obtained, it could be concluded that the requirements can be achieved by one of the following conditions:
1. Increasing number of rotor poles could be more beneficial.
2. Flux linkage can be increased with increasing turns in each rotor pole
3. Reducing the air gap to possible limits, usually restricted by mechanical failures.
Although the results are still not preferable for single engine aircrafts, this could be used in other application like wind turbines, micro-hydro and further research on the work is imminent.
44

CHAPTER 7
FUTURE WORK
The first step is to find out whether a rotor or stator is saturating. Measuring the rotor flux verses field current provides information about rotor saturation, which helps to identify the cause. The following methods could be used to improve the designed rotor:
1. Increasing the number of field winding turns: Adding more turns would increase output, but it also increase the resistance, which ultimately would increase the undesirable power loss in the system. If the rotor is saturating, increasing field winding turns does not help. Moreover, available winding space, limits the number of turns around the poles.
2. Increasing the number of pole: This may be the best possible solution for better performance. Increasing the number of poles increase frequency at a given speed. As mentioned in equation (9), increased frequency increases the generated voltage. It will be difficult to hand wind, if the pole number is increased.
Therefore, other winding methods should be considered.
3 Increasing the armature winding turns or increasing the wire size: Increasing the number of turns would definitely increases the generated voltage given by equation (9), and increasing the wire size would decrease the armature resistance. However, if stator saturation exists, increasing armature winding will not help.
3. Proposed method: Designing the appropriate number of armature winding turns and size could produce the required output with at most 1 mm of air gap. This would avoid the air gap losses, making the design more efficient. Also, it is
45

necessary to determine the amount of flux needed to produce the rated output with the designed stator. Then, the rotor should be designed to produce the required flux. Increasing the number of poles is recommended, high number of poles would increases the iron loss, so the number of poles should be carefully selected. The rotor material should be chosen carefully and should match the design requirements.
46

REFERENCES
47

REFERENCES
[1] K. Ing. and G. Burger, Automotive Electrics and Electronics Systems , 3rd ed.,
Robert Bosch GmbH, Stuttgart, 1988.
[2] Ward Jewell, Kasalika Eric, Sariah Bryson, Kopundo Gerald, and Lotri-Koffi,
“Design of Brushless alternator,” Senior Electrical Project Report, Department of
Electrical and Computer Engineering, Wichita State University, Wichita,KS, 2005.
[3] I. J. Nagrath and D. P. Kothari, Electric Machines , 2nd ed., Tata Mc Graw Hill,
New Delhi, 2002, Chapter 8.
[4] G. Karady and K. Holbert, “Tutorial: Energy Conversion and Transport” [online],
Lecture notes EEE 360 , Chapter 6, Synchronous machine, [cited 10 October
2006], available from World Wide Web:
<http://www.eas.asu.edu/~karady/360_stuff/Lectures/Lecture%2016%20Chapter
%206%20360_Synchronous%20Mach.ppt#448,3,Synchronous Machines>
[5] A. E. Fitzgerald, Charles Kingsley, Jr., and Stephen D. Umans, Electric
Machinery , 6th ed., McGraw-Hill, NY, 2003, Chapter 5.
[6] Robert L. Ames, A.C. Generators Design and Application , Research Studies
Press Ltd., 24 Belvedere, Taunwn, Somerset, England, 1990, Chapters 1-12.
[7] Ernest Mendrela, “Tutorial: Generation of Electric Energy” [online], Lecture notes
EE-3410 Electric Power , Fall 2003 [cited 10 October 2006], available from World
Wide Web: <http://www.ee.lsu.edu/mendrela/EE3410Electricgenerators.pdf>
[8] A. K Sawhney, Electrical Machine Design , 5 th
ed., Dhanpat Rai & Co.(P) Ltd.,
1710, Nai Sarak, Delhi-1160, 2001, Chapters 2, 10, and 12.
[9] D. V. Richardson, Handbook of Rotating Electric Machinery , Reston Publishing
Company, Inc., Prentice-Hall Company, Reston, Virginia, 1980.
[10] S. A. Nasar, Hand Book of Electric Machines , McGraw-Hill Book Company, Inc.,
Printed in USA, 1987.
[11] S. Ranjan, Step Up Converter for Variable Speed Synchronous Generator , MS.
Dissertation, Department of Engineering, Technical Institute of Denmark,
Denmark.
[12] Davidson Sales Electric Equipment and Accessories, “Datasheet” [online], [cited
23 March 2006], available from World Wide Web:
<http://www.davidsonsales.com/acrobat%20files/CoilPitch.pdf>
48

[13] Centre of Electric Machine and Power Electronics , “Tutorial: Electric Energy
Technology” [online], Lecture notes 48550, Chapter 6, Synchronous machine,
[cited 10 October 2006], available from World Wide Web:
<http://services.eng.uts.edu.au/cempe/subjects_JGZ/eet/eet_ch6.pdf>
[14] [cited 19 March 2006], available from World Wide Web:
<http://whatis.techtarget.com/definition/0,,sid9_gci759327,00.html>
[15] Port Richy,”Magnetism-Basic Electric Theory” [online], Parts Hanger, page 33,
[cited 17 October 2006], available from World Wide Web:
<http://www.tpub.com/content/doe/h1011v1/css/h1011v1_57.htm>
[16] Norberto Raggio, “Electromagnet Design Cookbook” [online], Buenos Aires,
Argentina, Updated June 21 1997, [cited 19 March 2006], available from World
Wide Web:<http://www.geocities.com/CapeCanaveral/2404/design2.html>
[17] [cited 23 March 2006], available from World Wide Web:
<http://en.wikipedia.org/wiki/Magnetomotive_force>
[18] Introduction to Magnetic Particle and Inspection, ”Permeability” [online], [cited 23
March 2006], available from World Wide Web:
<http://www.ndt-ed.org/EducationResources/CommunityCollege/
MagParticle/Physics/Permeability.htm>
49

APPENDICES
50

APPENDIX A
CROSS-SECTIONAL VIEW OF CLAW POLE ALTERNATOR
Cross-Sectional View
1. Collector ring and shield
2. Rectifier
3. Power diode
4. Exciter diode
5. Regulator, brush holder
and carbon brush
6. Stator
7. Rotor
8. Fan
9. Pulley
10. Drive and shield
51

APPENDIX B
BRIEF DISCRIPTION OF POWER ANGLE
Power Angle
If the resistance of synchronous machine as shown in equation A
1
is neglected, power at the terminal (P t
) and excitation (P e
) side will be equal. Electrical model of a synchronous machine is,
V t
= I a
R a
+ jX s
I a
+ E af
(B.1) where V t
is terminal voltage, E af
is a root mean squares value of excitation voltage, synchronous reactance, I a
is armature current, and R a
is armature resistance.
P t
= P e
=
E af
X s
V t sin δ (B.2) where δ is the phase angle between the terminal voltage and the excitation voltage which is called the power angle. The power delivered by synchronous machine can be increased also by increasing the power angle, but the maximum angle permissible is
52

APPENDIX B (continued)
Figure B
1
: Power angle characteristics.
Electromagnetic Torque
The active power is given by
P = mVI a cos ϕ (B.3) and reactive power is given by
Q = mVI a sin ϕ (B.4)
For the synchronous machine
X s
I a cos ϕ = E f sin δ
I a cos ϕ =
E f
X s sin δ
Putting the value of I a cos ϕ in equation B
1
yields
P = m
VE f
X s sin δ
(B.5)
(B.6)
APPEDDIX B (continued)
53

The torque developed at the terminal when the stator is neglected is given by
P
T = w s
(B.7)
Here, power developed at the terminal is an air gap power.
From equations (B.6) and (B.7) we get m
T = w s
VE f
X s sin δ , which is an electromagnetic torque which is also denoted as T
Em
.
54

APPENDIX C
CONSTRUCTION OF FOUR-POLE SALIENT POLE ROTOR
Cast steel was chosen for salient pole rotor. For the simplicity of design and construction, it was decided to build a four-pole salient pole. Layout was designed in
CATIA V5R17. The rotor was constructed at the Industrial Manufacturing Laboratory with the instruction of Mr. Larry Morton.
C.1 Process of Construction
1. Four pole rotor was chosen suitable for design.
2. Choose from the variety of CAD or engineering drawing software to design the rotor.
3. According to the need and availability, consider the different types of metal to be used. Cast steel was used in this study. Usually cast steel is available in a rectangular shape in a variety of dimensions. Choose the suitable piece.
4. Ensure that there are at least two or three such pieces, in case the rectangular piece (job) is spoiled.
5. Choose from a variety of machines and techniques according to the availability of machines and labs.
6. Conservative technique was used to build the rotor.
7. After using the milling machines, use a metal file to smooth the edges. A flat bastard file is preferred.
8. Use proper insulation to prevent a short circuit between the field winding and the rotor. One way to insulate is to put glass around the winding area.
55

.
APPEXDIX C (continued)
Acer (Dynamic 1340 G) lathe machine was used to remove the edges of job and develop a circular piece with correct dimension.
Turrent (S#1473) milling machine was used to make slots. Circular disc was used to rotate the job accordingly.
Circular disc
Turrent (S # 147041) milling machine was used to make the winding space in the rectangular shape rotor. Make sure the winding space is enough for desired winding. It is preferred that the cut be deeper than the desired one.
56

APPENDIX D
TECHNICAL INFORMATION ON GLASS TAPE
57

APPENDIX D (continued)
58

APPENDX E
CALCULATING PITCH FACTOR AND DISTRIBUTION FACTOR
E.1 Coil Pitch [9] [12]
Coil pitch is the distance between the two sides of an individual coil of an AC armature winding. Coil pitch affects the magnitude of voltage induced in the coil.
Generally, there are two types of coil pitch in an AC armature winding.
E.1.1 Fractional Pitch Winding
As shown in Figure E.1, the angular distance between the centers of the adjacent field poles (90 ° mechanical) is greater than the angular distance between the sides of a coil (angle A, 60 ° ). Such winding is called a fractional pitch winding. Equation (E.1) shows the relation between the electrical degree and mechanical degree, 90 ° mechanical is equal to 180 ° electrical for four pole rotor. Therefore the coil pitch is 2/3 pi, i.e., is 60 ° /90 ° or 120 ° /180 ° .
θ e
=


P
2


θ m
(E.1) where
P = number of poles
θ e = electrical degree
θ m = mechanical degree
59

APPENDIX E (continued)
Figure E
.
1: Fractional pitch winding [12].
E.1.2 Full Pitch
As shown in the Figure E.2, the angular distance between the centers of adjacent field poles is equal to the angular distance between the sides of the coil. Therefore, the coil pitch is 1, i.e., is 90 ° /90 ° or 180 ° /180 °
Figure E.2: Full pitch winding [12].
60

APPENDIX E (continued )
E.1.3 Pitch Factor Calculation [12]
The pitch factor is
Pitch Factor(K p
) =
Coil throw − 1 (Coil span)
Slots per pole
(E.2) where coil throw is the number of slots covered by the coil when the slot are numbered consecutively around the circumference of the stator as shown in Figure E.3 [9]
Figure E
3
: AC armature winding. where Coil span is the measurement of number of core slots between sides of the coil.
If the coil throw is 1 to 9, then the coil span is 8 slots (9-1). Figure E.4 is a coil arrangement of 60 slots for six-pole machine [12]. where slots per pole are the number of slots present in armature winding divided by the number of poles in the field winding.
61

APPENDIX E (continued)
Figure E.4: Fractional pitch lap coils (100% for comparison).
E.1.4 Distribution Factor
When several coils in a pole group are connected in a series or phase belt with more than one coil, this tends to decrease the voltage induced in the phase belt. This is usually due to the space-phase relationship. For example, if there are two coils, the sum of voltage induced in two coils will be less than twice the voltage induced in a coil [8, 5]. distributi on factor (K d
) = sin (n α n α /
= n sin ( α /2)
E pg
E c
(E.3) where
α = number of electrical degree between the slots n = number of slots per pole per phase
E pg
= phasor sum of coil voltage per phase
E c
= arthematic sum of coil voltage per phase
62

APPENDIX E (continued)
Figure E
.
5: Coil distribution factor of four slots/pole/phase.
For a three phase, α =180/3n
63

APPENDIX F
DIFFERENT VIEWS OF ROTOR LAYOUT 1 AND 2
F1 Rotor Layout 1 (dimensions are in mm)
64

APPENDIX F (continued)
F2 Rotor Layout 2 (dimensions are in mm)
65

APPENDIX G
EXCEL SPREADSHEET OF DATA MEASURED
G.1 Claw Pole Rotor
The following shows OCC and SC test data. Vf = field voltage for rectifier output,
If = field current
1 for measurement after and 2 for measurement before rectification
8.1
9.3
10.7
11.4
12.9
14.5
16.4
17.7
Vf1
1
2
3
4.1
6.2
7
19
0.5
0.57
0.66
0.71
0.82
0.99
1.1
1.23
If1
0.06
0.13
0.18
0.26
0.35
0.4
1.32
22
23.4
25
25.5
26.4
27.5
27.9
28.3
Voc1
2.82
6.28
9.62
11.19
16.92
19
28.5
7.5
8.1
9.1
10.2
11.4
12.2
13.2
14.5
Vf2
1
2.1
3.1
4
5.1
6.7
15.4
0.43
0.47
0.54
0.6
0.7
0.76
0.83
0.9
If2
0.02
0.07
0.13
0.18
0.26
0.36
0.99
Voc2(peak) Voc2(rms)
2.2 1.6
4.4
7.4
3.1
5.4
9.6
12.4
16.7
6.9
8.8
11.9
18.7
19.7
21.8
23.8
24.1
24.8
25.4
25.8
26.2
13.4
13.9
15.7
16.3
17.4
17.9
18.2
18.6
18.9
If1
0.06
0.1
0.16
0.2
0.26
0.35
0.4
0.5
0.57
0.66
0.71
0.82
0.99
1.1
1.23
1.32
Isc1
2.7871
4.8671
7.9871
10.0671
13.1871
17.8671
20.4671
25.6671
29.3071
33.9871
36.5871
42.3071
51.1471
56.8671
63.6271
68.3071
If2
0.02
0.07
0.13
Isc2
3.17508
5.39703
8.06337
0.18 10.28532
0.26 13.84044
0.36 18.28434
0.43 21.39507
0.47 23.17263
0.54 26.28336
0.6
0.7
28.9497
33.3936
0.76 36.05994
0.83 39.17067
0.9 42.2814
0.99 46.28091
1.04 48.50286
66

APPEXDIX G (continued)
Flux measurement data is as follows:
Flux in
Gauss
95
102
97
138
116
148
199
155
124
97
106
116
97
122.3076923
G.2 Salient Pole Rotor
The following shows OCC and SC test data; 1 for 100, 2 for 200, and 3 for 400 turns of field winding
Vf1
1.19
2.02
3.06
4.11
4.5
If1
0.7
1.33
2.09
2.82
3.14
Voc1
0.0245
0.1905
0.489
0.81
0.94
Vf2
1.26
2.12
3.11
4.06
5.04
6.35
7.07
If2
0.39
Voc2
-0.06832
Vf3
1.34
0.86 0.353694 2.19
1.4 0.83856
1.84 1.233636
3.23
4.6
2.2 1.55688 5.46
2.52 1.844208 6.06
2.96 2.239284 7.49
If3
0.24
0.44
0.71
1.07
1.29
1.5
1.88
Voc3
0.11
0.38
0.8
1.57
2.05
2.41
3.16
If1 Isc1 If2
1.26
1.65
1.4E-06
1.82E-05
0.7
0.9
2.26 0.000151 1.46
3.11 0.064 2.18
2.7
3.08
3.15
Isc2 If3
3.2E-06 0.35
0.000073 0.64
0.0123
0.375
0.89
1.21
1.052
1.703
1.843
1.51
1.92
2.13
Isc3
6.3E-06
0.0013
0.0945
2.06
3.64
5.72
6.83
67

APPENDIX G (continued)
Flux measurement data is as follows:
A for 100, B for 200, and C for 400 turns of field winding. Unit of flux is Gauss.
A
19
22
16
24
29
25
33
36
B
42
58
44
53
67
56
49
64
C
31
27
47
74
64
52
30 59 68
26.54545 55.72727273 68.81818
59
47
72
93
57
84
91
70
After the addition of series resistance to make it 13.6 Ω .
A
1.4
1.7
1.8
1.9
0.8
2.1
1.2
1.8
1.5
1.7
1.6
B
7
9.3
11.1
7.2
4.8
5.6
6.7
7.6
8.2
8
7.9
C
9
6
10
7.5
8.1
11.6
6.2
8.8
9.4
9.7
9.9
1.590909 7.581818182 8.745455
Salient pole OCC and SC tests with addition of pole shoe data
Short circuit tests 1, 2 and 3 respectively denote 200, 400, and 800 turns field winding.
Unit of current is ampere.
68

APPENDIX G (continued)
If1
0.44
Isc1
3
If2
0.29
Isc2
3
If3
0.15
Isc3
3
0.54
1.33
2.19
2.83
3.54
3.94
3
6
10
11
14
15
0.5
0.79
1.02
1.27
1.57
1.84
5
7
8
10
13
14
0.28
0.44
0.55
0.68
0.8
0.99
5
7
9
11
13
15
4.51 17 2.14 16 1.26 19
Open circuit voltage test. 1, 2, and 3 denotes 200, 400, and 800 field winding turns, respectively.
Vf1
1
2.1
3.2
4.4
If1
0.39
0.86
1.4
1.84
Voc1
1
2
3.2
4.3
Vf2
1.3
1.8
3.7
4.3
If2
0.32
0.44
0.87
1.03
Voc2
1.1
1.8
4.1
4.8
Vf3
0.8
1.7
2.6
3.2
If3
0.08
0.2
0.32
0.39
Voc3
0.8
1.8
2.9
3.5
5.1
5.9
6.9
7.5
8.3
9.2
10.3
11.4
2.2
2.52
2.96
3.33
3.63
4.05
4.56
5.123
5
5.7
6.4
6.9
7.5
7.9
8.4
9
5.2
6.7
8.3
10.3
11.8
13.2
15
16
1.26
1.67
2.21
2.63
3
3.37
3.79
4
5.7
7.1
8.3
9.5
10.1
10.5
11
11.1
4
5.4
6.3
7
8
9
10.2
11
0.5
0.69
0.79
0.88
1.01
1.13
1.27
1.39
4.5
6
6.6
7.2
8
8.6
9.2
9.7
69