\FERFORMANCE MEASUREMENTOF A TEN KILOWATT

HORIZONTAL AXIS WIND TURBINE,”

4

by

Thomas E.\Benim„

Thesis submitted to the Graduate Faculty of the ,

Virginia Polytechnic Institute and State University 4

in partial fulfillment of the requirements for the degree of

MASTER OF SCIENCE

inI

Mechanical Engineering

APPROVED:Q (j?. F. 0'Brien,/Ur.

H. L. Moses H. L. Wood

September, 1977

Blacksburg, Virginia

㤠II. ACKNOWLEDGMENTS

Tii

III. TABLE OF CONTENTS

E9.;I. TITLE .......................... i

II. ACKNOWLEDGMENTS ..................... ii

· III. TABLE OF CONTENTS . . .................. iii

IV. LIST OF FIGURES ..................... v

V. LIST OF TABLES ....._ ................ vii

VI. NOMENCLATURE ......................viii

VII. INTRODUCTION ...................... l

VIII. REVIEW OF LITERATURE .................. 3

Overview .......... 3

Wind Energy Aerodynamics ............... 6

Wind Energy Conversion and Storage .......... ll

IX. DESCRIPTION OF SYSTEM .................. T3

Overview ................‘....... I3I

Electro WVG—l20G Wind Generator ............ I3

Performance Predictions .............. 22

Control System 22

Resistive Load Bank .................. 25

Battery Bank .....,............... 26

Electrical Output Measurement System ......... 27

Wind Measurement System ................ 30

X. DATA .......................... 40

XI. DISCUSSION ....................... 58

Interpretation of Data ................ 58

iii

Bee;Load Switching and Sizing ............... 62

Battery or Direct Load ................. 63

Power Multiplier Integrator ............V. . 63

x11. conctusrows.......‘................ 64

XIII. RECOMMENDATIONS FOR FURTHER RESEARCH ........... 65

x1v. LITERATURE cnsu....._. ._..............66

xv. APPENDICES.......;................68Appendix A. Specifications of Electro wVG—l20G .... 69

Appendix B. Electrical Schematics of Electro WVG-l20G 472

Appendix C. Resistive Load Calibration Data ...... 77

Appendix D. Specifications of Nife C360O Battery . . . 80

Appendix E. Measurement System Calibration Data .... 82

Appendix F. Uncertainty Analysis ........... 87

Appendix G. List of Equipment ............. 9l6

xv1. VITA...........................93ABSTRACT

6iv

IV. LIST OF FIGURES

wsI. Typical Performance of wind Power Machines. 5

2. One Dimensional Flow Past a wind Turbine. 8

3. Rotor Augmentation Devices. IO

4. Cooling System Schematic. I2

5. MVG-l2OG wind Turbine and Test Site. I4

6. Test Site Building Layout. ‘ I5

7. Electrical Power Distribution. I6

8. Clark—Y and wVG-l2OG Airfoils. l8

9. Blade Element Velocity Triangle. 20

IO. Angle of Attack vs. Radius at Various Values of X. 2l

ll. Computer Prediction of MVG-I2OG Performance. 23I2. Block Diagram of Performance Measuring System. 28

I3. Signal Conditioning Circuit. 29

I4. Multiplier Patching Circuit, (V x I = P). 3l

I5. Stewart Anemometer. 33

I6. Detail of Stewart Anemometer Modification. 34

I7. Belfort Recorder Input Modification. 36

l8. Schematic of Integrated Circuit Odometer. 377

I9. Integrated Circuit Odometer. 38

20. Performance Data, Case I. 45

2I. Performance Data, Case 2. 46

22. Performance Data, Case 3. 47‘

23. Performance Data, Case 4. 48

24. Performance Data, Case 5. 49

v

Bass25. Performance Data, Case 6. 50

26. Performance Data, Case 7. 51

27. Performance Data, Case 8. 52.I

28. Performance Data, Case 9O I

53

29. Performance Data, Case 10. 54

30. Performance Data, Case 11. 55

A 31. Performance Data, Case 12. 56

32. Performance Data, Case 13. 57

33. Mean Power Output Curve, Resistive Load. 59

34. Mean Power Output Curve, Battery Load. · 60

Appendix Figures

A1. wVG—120G Generator Characteristics. 71

B1. WVG-12OG Contro1 Circuit. 75

B2. WVG-1206 Load Contactor Board. 76

vi

V. LIST OF TABLES

Bass1. HVG—120G B1ade Measurements and C1ark-Y Specifications 19

2. Performance Test Case IdentificationI

41”

3. Performance Data Summary 42

4. Power Output Summary 61

» APPENOIX TABLES

A—1. Specifications of E1ectr0 MVG-120G wind Generator 70

B-1. E1ectrica1 Schematic Legend 73C—1. 1000 W Resistive E1ements 78

C-2. A1ternate Resistive E1ements 79

D—1. Specifications of Modified Nife C360O Battery 81

E—1. Vo1tmeter Ca1ibration Data 83

E-2. Ammeter Ca1ibration Data 84

E-3. E1ectrica1 Measurement System Ca1ibration Data 85

G-1. List of Equipment 92

vii

VI. NDMENCLATUREL

A Area

a Axial Interference Factor

Bmax Maximum Thickness of Blade SectionC Chord Length

CP Power CoefficientD Distance from LE to BmaxE Kinetic Energy

f Frequency

I Current

L Length ·

L' Lift Vector

L/D Lift/Drag

LE Leading Edge Thickness

m Mass

P PowerL

P„ Total Power of wind at Vw

R Rotor Radius

r Blade Element Radius

t Time

TE Trailing Edge Thickness

u wind Speed at Rotor PlaneL

ul Final wind Speed

V„ Free Stream Velocity

W Measurement Uncertainty

viii

w' Relative wind Velocity

X Tip Speed Ratio

6 Angle of Attack

p Density

6 Standard Deviation

6 Blade Pitch

Q Angular Velocity

i x -

VII. INTRODUCTION

wind has been used for centuries to propel boats, pump water,

and, more recently, as a source of electrical power. The use of wind

turbines to generate electricity has been limited to remote areas

because of the availability of cheap, reliable electrical power in

most developed countries. The dwindling supply and increased cost of

fossil fuels, coupled with the unfulfilled dreams of unlimited nuclear

power have prompted increased interest in all types of wind turbine

generators.

work is currently underway at Virginia Polytechnic Institute and

State University (VPI&SU) to build a wind-powered, refrigerated, apple

storage facility. This project, sponsored by the Agriculture Research

Service, United States Department of Agriculture, is a feasibility .

project to study the merits of wind power fpr apple Stprage applica-

tions. .

Since the purpose of this project is to apply wind power to a

specific use, a commercially available windmill was purchased, so that

design efforts could be concentrated on the energy storage and refrig-

eration systems. After initial design considerations and wind velocity

surveys, it was decided to purchase an Electro] wVG-l2OG wind .

generator which has a peak output of lO kw. [l]2

1 Electro, G.m.b.H. winterhur, Switzerland.

2 Numbers in brackets refer to references listed in LITERATURE CITED.

l

T 2T

Data concerning the performance of the wind generator were incom-

plete and tended to be stated in general terms. Specific performance

data are essential to the evaluation of the overall project's success.

~This thesis is concerned with the development of the windmill testing

facilities at VPI&SU and the initial performance testing of the

Electro wVG-l2OG wind generator.

VIII. REVIEW OF LITERATURE

Overview

Although wind turbines have been used for centuries, the modern

development of wind turbines (particularly for the generation of

electricity) began at the close of World War I. According to Putnam

[2], early investigators studied three types of wind turbines: The

spinning cylinder (Magnus effect), the Savonius rotor, and the

propeller type. Modern literature divides windmills into two broad

categories designated by the orientation of the rotor axis to the

ground, i.e. vertical axis or horizontal axis. Some researchers

refer to vertical axis wind turbines as crosswind-axis machines and

horizontal axis turbines as wind-axis machines.

The two most popular vertical axis rotors are the Darrieus rotor

and the Savonius rotor. The Darrieus rotor is somewhat more

economical to build in terms of material used, but the Savonius rotor

is popular with individual experimenters due to the ease of construc-

tion using readily available materials. The advantages of vertical

axis wind turbines are two. First, they are sensitive to winds from

any direction and can respond to gusts without being oriented to theU

direction of flow. Second, the generator can be located at the base, ‘

reducing Structural loads. ‘

A large Darrieus wind turbine l9 m (62 ft) high and l7 m (56 ft)

in diameter is currently being tested at Sandia Laboratories. The

3

4

wind turbine is expected to produce 60 kw in a l2.5 m/s (28 mile/h)

wind [3].

Two common examples of horizontal axis wind turbines are the

American farm windmill and the Dutch windmills. Both of these produce

high torque at a low rotational speed making them ideal for driving

pumps and other machinery. To drive an electrical generator a 2-

or 3—bladed, high speed wind turbine is more effective since less

gearing is required. High speed wind turbines also are able to

extract more of the wind energy. Figure l shows performance character-

istics vs. tip speed ratio for several types of wind turbines.

Many large-scale horizontal axis wind turbines have been built

as test units. The largest was the Smith - Putnam wind turbine, built

in Vermont during world war II [2]. The machine had a capacity of

l.25 Mw and was operated more than ll0O hours before a blade failure

caused cancellation of the program. The notoriety of this turbine

lies not with its material failure but with its success at proving

that a large wind turbine can be interfaced to a commercial utility

network.

Large horizontal axis wind turbines have been constructed with

the rotor plane upwind and downwind of the tower [4]. The downwind

orientation provides an improved safety margin since the blades canin

flex in a strong wind without hitting the tower. However, the wake

of the tower can induce periodic stresses in the blades, which may

cause premature failure. This problem is being studied at Sandusky,‘

Ohio by NASA engineers of the Lewis Research Center.

5

10.6 _

xx .«>8 0.5 Ideal Efficiency for Propeller

>- Type windmillsL <Z ·GJ Q.sO N‘°' Z?0.4ii

High Speed Two Blade_ de American Multi- Type

+: 0.3 ;9 Blade Type _° _ä‘

- Savonius Rotor Mx_g .

” „/”Darrieus Rotor

Q, aug O . 2 i, /ä¤ä

0.]I ,Dutch_Four Arm Type

„ Q-”

0 l 2 3 4 I 5 6 7-

Speed Ratio = Tip Peripheral Speed/Stream Speed

Figure l. Typical Performance of wind Power Machines.(From Reference 8)

6

while development efforts of large wind turbines command most of

the current attention, the largest conmercially available wind turbine

is rated at approximately lO kw output. The need for small wind

energy systems, particularly for agricultural use, has been pointed

out by Rueth [5] and Liljedahl [6].

wilson [7] points out the need for research on production wind-

mills, citing the fact that no performance data are available except

some rather limited figures from manufacturers. In addition to

performance, cost and reliability of commercial units must be im-

proved. ‘

wind Energy Aerodynamics

Fundamental windmill aerodynamic theory has been developed from

one dimensional momentum theory. The basic ideas of this theory

are outlined below.

The kinetic energy of an airstream of mass, m, and velocity, Vw, is

l 2E =·2—lllVmIf

p is the density, A is the cross—sectional area of the air-

stream, and L is a reference length, then

E = %pALvw2 (2)

But L can be expressed asV

L = vwt (3)

. 7

Since power is the time rate of change of energy, using Equations (2)

and (3),

-ü=l 3Pw —dt 2 pAVw (4)

Following the axial momentum approach of Wilson and Lissaman [8]

and referring to Fig. 2, —

. Vw T uiU (5)

The power extracted from the airstream is given by( V

»>=P—’¥!<v+¤><v—¤> <6>2 ¤¤”l‘

¤¤ ]

If we define an axial interference factor (ö), so that

Vw - u = a Vw (7)

and

2a Vw (8)

Power can be expressed as

P = g-p AVw3[4 a(l -a)2] (9)

A power coefficient, Cp, can now be defined as >

Cp - Pw (l0)

Thus,

C = --4-- = 4a(l - a)2 (ll)P )AV3Üpw

8

vw

Streamline

·

I)— >!——-—————-— U:>-————-—-uw —

? .,__|

Ij Rotor Disk

1I

Figure 2 . One Dimensional Flow Past 6wind Turbine. (from Reference 8)

9

CP has a maximum value of 0.593 when a = l/3.‘

A real windmill imparts a rotational velocity to the wake in

addition to the axial momentum change. The losses due to induced

angular momentum are greatest at low tip speed ratios (X).

X

EReferringagain to Fig. l, it is seen that high speed wind

turbines exhibit higher values of Cp. However, at values of X above

6 the effects of aerodynamic friction cause the efficiency to drop.

Thus, it is imperative to have blades with good L/D characteristics

in high speed wind turbines. -

Wilson and Lissaman [8] present a computer program designed to

allow rapid comparison of the aerodynamic performance of horizontal

wind turbines. Their program includes models for tip losses and hub

losses, and uses a modified blade element theory approach.

Much research has been done on the use of ducts to increase

wind turbine performance. According to Oman and Foreman [9],

dynamic stability problems of large rotors limit the conventional

wind turbine to a size of about l WW. By use of a diffuser duct,

rotor disc axial velocity can be increased to provide up to four times

the power output for the same size rotor.

Smulders [l0] reports that small airfoils added to the rotor tips

can produce up to twice the conventional power output, using only 2

per cent of the material needed for a diffuser duct. Figure 3

illustrates a duct and the tips.

TO

r"II',RotorDi scäxVw -—-—a» ·§ ·- · .

""-~\Ducted wind Turbine

c:¤*Rotor {Di

scimRotor with Tips

Figure 3. Rotor Augmentation Devices.

Ill

° wind Energy Conversion and Storage

VSince a conventional horizontal axis wind turbine can extract

59 per cent of the wind's kinetic energy at best, and since the wind

is not always blowing, research is also being directed at the problem

of energy conversion and storage.A

Two of the most common forms of energy conversion are the direct

drive of pumps and the generation of electricity. Energy storage

for these systems consists of holding tanks and batteries, respectively.

Zlotnic [ll] reports on recent advances in energy storage in

electro-chemical, flywheel, and compressed air systems.

Blanton [l2] describes a composite storage system using both

batteries and thermal (ice) storage. This system (Fig. 4) uses a small

battery storage system to run air circulating fans, while an ice _

storage system stores the bulk of the energy needed to cool an apple

storage facility. His design will be used in conjunction with the

Electro HVG-l2OG wind turbine described in this thesis.

12

Storage batteries‘I 15500 w-hT I

IV | '

- 1. I wjpd generator I I

I Maximum output 10 kw I I I I _· 1 I L L-; L-; L-; L-; {

L-.-.-.---------.--.--0.2-.-...-.-.----------g_ I

II] EI] EI] EI] CI] CI] EI] EI] [II I. IEvaporator II] 2 ————«

0.37 m face area I0 Ü :

~ 1[J [I uCondensin Unit I

_ [I _EI

7000 w capacity I

[I Circu1atinFanÜ

2040m3/h EQQQIQEDIEILQ[I 0.12 kw [IÜ Q Q Q Q Q I;] IQI] _____ Storage Room

Ü ‘I 1008 busne1 capacity

“1·*lIII1lHIlIIIlIll6·“Therma1 energy storage unit

Capacity 2.8x105 w—h

Figure 4. Coo1ing system schematic.(From Reference 12)

IX. DESCRIPTION OF SYSTEM -

Overview

The Electro wVG-l2OG wind generator and a transportable test

center were temporarily erected on the VPI&SU campus to provide a con-

venient location for initial evaluation of the windmill. Figure 5

illustrates the site and the complete windmill test system.

The wind turbine was supported by a 27 m (90 ft) guyed tower. Two

anemometers were mounted on either side of the tower at a height of 2l m

(70 ft). This location placed the anemometers 3 m (10 ft) below the

swept area of the blades. A weatherproof control box mounted at the

base of the tower contains a drive motor which positions the tail fin of

the wind turbine via a steel cable routed up the interior of the tower.

Figure 6 shows (from left to right) the instrument building,

the resistive load bank shelter, and the battery shelter, Figure 7

is a block diagram of the electrical distribution system as described

in this thesis. The instrument building contains the rectifiers and

the main control box of the wind turbine, as well as all instrumenta-

tion. The building is heated and cooled, as necessary, to maintain a

proper environment for electronic equipment. Each subsystem is de-

scribed in detail in the following sections.

The windmill, tower, and buildings were moved in late Summer l977

to the apple storage site located at the VPI&SU Horticulture Farm.

Electro wVG-l20G wind Generator I

The Electro wVG-l20G is a three-bladed, horizontal-axis wind

turbine with a maximum rated output of lO kw. Although it is called

l3

I6

Tower

I II I I-

II windmill II Alternator I. I

: IR s T I

| w In III |I I Instrument BuildingI I

I-_-_-_-__.--I

I IRIIII :I Automatic lm. C¤ntI^¤l I

II Vane Control I I

IBox |

IIII · I IL...........IJ..I··—••··I

I"*****“****"'°“"""**1, I II I I Direct Load II I I II

I II LoadlII ‘ III

I L" IS" Load? III—'•'ElI ‘

° 9 • ivI**:.—IgII I . . I I II II

I SI II’ I ’

I I I“

II I II I I é' é I i ti Ii ·‘$' $ IE ‘I III I I I I I I I I] · I

'

-6 l•

QO:BII I

Figure 7. Electrical Power Distribution.

l7V

a wind generator by the manufacturer, the primary electrical output is

3—phase alternating current.‘ Specifications for the wind generator

are listed in Appendix A.

The blades are made of laminated fir and are roughly shaped to a

Clark—Y airfoil (Fig. 8). Note that the leading edge is essentially

blunt. Blade measurements taken from one of the blades delivered with

the windmill are listed in Tablel.“

Corresponding specifications for

a Clark—Y airfoil are listed at the bottom of the table. „

The pitch (6) of the blades at the root is l4.5° and varies

nearly linearly to 5° at the tip. Referring to Fig. 9, it is seen

that the angle of attack (o) of a blade element is dependent on the

rotational speed, the radius of the element, the pitch of the blade,

and the wind speed at the rotor plane.)

Maximum performance of the Clark-Y airfoil is obtained at an

angle of attack of about O.5° [l3]. The Clark-Y airfoil maintains a

fairly good L/D ratio (> l6) from an angle of attack of -3° to 8°. V

Figure l0 shows the angle of attack of the MVG-l2OG blades as a

function of section radius for several values of tip speed ratio.

Since 75 per cent of the wind energy is contained in the area swept by

the outer half of the blades, it is paramount that this portion of the

blades, at least, operates efficiently. Figure lO shows that the angle

of attack of the outer 50 per cent of the NVG-l20G blades is in the

desirable.range at tip speed ratios from 6 to 8.

18

Clark-Y Airfoil

. 6D „LEI ’¤

TE\!7«—.1ET . . . TWVG-T20 G Airfoii (Typicai) _

Figure 8. Clark-Y and NVG-120 G Airfoiis.

l9

Table l

wVG—l20G Blade Measurements and Clark-Y Specifications

NVG;l20G Blade Measurements (Note):

DistanceFrom Root, C, LE/C TE/C Bma /C _ D/C

m(in) mm(in) _ X

0.0o(o) l98(7.8) 0.24 O.]7 .24 0.0

0.3l(l2) 200(7.9) 0.l9 .l3 .l9 .l30.6l(24) 200(7.9) 0.l3 .05 .l7 .3]

0.9l(36) 200(7.9) 0.06 .0l .l2 .3]

l.22(48) 200(7.9) 0.06 .0] .ll .3l

l.52(60) 200(7.9) 0.06 .0] .09 .33

l.83(72) 200(7.9) 0.06 · .0] .09 .35

2.l3(84) 200(7.9) 0.04 .0l .l0 .35

2.44(96) l95(7.7) 0.04 .0l .08 .35

2.59(l02) l95(7.7) 0.04 .0] .ll .38

2.74(l08) l78(7.0) 0.04 .0l .ll .38

2.82(lll) l50(5.9) 0.05 „ .03 .ll .39

2.90(ll4) ll7(4.6) 0.07 .04 .ll .43

2.92(ll5) 6l(2.4) 0.l2 .l2 .ll .58

Clark-Y Specifications:

LE/C = 0.02 (radius)” l

TE/C = 0.00]

Bmax/C = 0.l2D/C = 0.30

~

Note: Refer to Figure 8 for symbol identification.

20

y AwindDirection

4

V0 E E Direction‘ \” I of Rotation6 I

w' ,0L (1-a)v__¤

Figure 9. Blade Element Velocity Triangle.(from Reference 8)

2l

50-

Q.an

' S40

. III s:

«¤I 5%

g 30 | gg0{ I H T

C° II g I r

ä I I1: ZU 1< I I

. =·— I° Icu I

IT5 IC I :4

" io I III X=6 I

: =8 I0 I

0.0 0.2 0.4 0.6 0.8 l.0

Rotor Blade Radius, r/R

IIOIZG: VCIIUES SI'IOWI"I öSSUI'II€ H0 äX'IäI InIC€YI°€Y‘€IIC6 äfldno pitch change by feathering mechanism.

. Figure lO. Angle of Attack vs. Radius at VariousValues of X.

22

Performance Predictions

The wind turbine analysis program described in Reference [8] was

modified by Mr. Reg Figard of the VPI&SU Aerospace and Ocean

Engineering Department for use on the VPI&SU computer. Results from.

this program using the NVG-l2OG blade geometry and the Clark-Y airfoil

are plotted on Fig. ll for tip speed ratios of 4 and 8, along with the

output power curve of an ideal windmill with the same blade radius.

Note that these curves only represent power extracted from the wind and

do not include mechanical or electrical losses incurred during energy

conversion and transmission.

IControl System

Since a windmill must operate over a wide range of wind speeds,

some provision must be made to match the load to the available power

in the wind, and to vary the operating characteristics of the wind

turbine. The control system provides this capability, as well as pro-

viding automatic shutdown in out-of-specification conditions. The

electrical system and automatic control schematic is shown in Appendix

B.

when charging a battery the load matching is simplified since

_ the battery can accept a large range of charging current at a rela-

tively constant voltage. However, protection must still be provided

against overcharging or overspeed of the wind turbine. If the wind-

mill is directly powering a resistive load, the control problem is

much more difficult. As the wind speed changes, the windmill speed

23

T2

10

Idea] windmill X = 8

3 - X = 6T?E

'

*4-

'U 6Q)

4-*Ur¤L+»X ,

1.1.1

Q A3“Q-2

0 4 9 . 13 'I8 _(0) (T0) (20) (30) (40)

wind Speed, m/s (mile/h)

Figure 11. Computer Prediction of WVG-1206 Performance.

24I

and voltage vary, as well as the current. A load that can dissipate

the rated output draws too much current at low wind speeds, preventing

the wind turbine from reaching optimum rotational speed.

The Electro machine was furnished with the capability to charge

batteries or to directly power a load. The resistive load was divided

into three sections; a "Direct Load" to be connected at all times,

"Load l" to be connected at higher wind speeds, and "Load 2" to be

connected at even greater wind speeds, The load bank is described

in detail in the next section.

To achieve the switching necessary to insure that the proper

load is connected, relays were provided·that sense the output voltage.

when the voltage reaches l20- l35 V DC, Load l is connected. when

the voltage rises to l40- l55 V, Load 2 is added to the circuit.

Figure B-2 illustrates the switching relays and load contactors. ·

During initial testing with the resistive loads, severe relay chatter

was observed which necessitated the addition of a 450 pF capacitor

across each coil. This modification, shown in Fig. 3-2, made the load

switching much smoother. with the battery bank in place it was

necessary to protect it from being overcharged. This was done by

removing the Direct Load and Load l from the system, allowing Load 2

to be connected automatically at l40— l55 V.

The Electro wVG-l20G is equipped with a propeller feathering

mechanism that is centrifugally actuated at high rotational speeds.

The feathering mechanism helps to prevent overspeed in high winds or

in the event that the load is lost. Data are not available on the

25

pitch change vs RPM, but pitch can increase about l0° from the initial

setting. s

There are three conditions which will cause the automatic control

to actuate the cable drive system mounted at the base of the tower,

turning the windmill fully or partially out of the wind. These are

overvoltage, overcurrent, and high wind. The overvoltage circuit

energizes at about T60 V, the overcurrent at 65 A, and the wind

sensor at about T8 m/s (40 mi/hr). All of the above limits can be

adjusted about l0%, although caution is recommended by the manufacturer

if they are increased. Once the windmill is turned out of the wind,

it will remain thus until the automatic timer energizes the starting

circuit. This occurs every 6 hours.

Resistive Load Bank

The resistive load bank, shown in Fig. 7, consists of ten pairs

of l3.5 ohm heating elements. Each pair is rated at T kw at T65 V.

The load bank was initially set up according to the windmill manu-

facturer's recommendations:

Direct Load (DL) — 20%

Load T ( T) - 30%

Load 2 ( 2) — 50%

Each pair of resistors is connected by a knife switch to the circuit,

allowing the operator to vary the load. This feature is useful for

studying the effects of load size and load switching on system

26·

performance. The resistors are mounted in ceramic light sockets

allowing easy substitution of various-sized units for further experi-

mentation with load sizing.

Appendix C contains power dissipation data for three different

sizes of resistive loads. Figures 20 through 25 show the effect of

different resistive loads on the performance of the wind generator.

UBattery Bank

The battery bank used was a modified Nife C360O nickel cadmium

battery consisting of 91 cells. The specifications for this battery

are contained in Appendix D. ·

Nickel cadmium batteries are ideally suited for windmill applica-

tions because they are not damagéd by deep discharging, their usable

voltage range is relatively large, and they can be charged indefinitely

if the maximum voltage is not exceeded. The chief drawback to nickel

cadmium batteries is that they cost much more than lead acid batteries.

Referring to Appendix D, the battery system has the following

characteristics -

Maximum Peak Voltage: 157 V

Maximum Continuous Voltage: 141 V

Minimum Allowable Voltage: 100 V

Maximum Charging Current: 34.6 A

Efficiency: = Zgiäshäxgg-= Tlééäägäéig = 54%charge ' °

Average Discharge Voltage: 1.2 x 91 = 110 V

Available Stored Energy: 13.1 kw-h

27

The efficiency and available stored energy can be increased by 5 per

cent if the discharge rate is reduced to l5 amps or less.

Electrical Output Measurement System

Since the final criterion in judging whether a wind generator isIoperating correctly is its power output, a system was developed to

display and record critical electrical parameters. Figure l2 is the

block diagram of this system. The parameters measured were voltage,

current, frequency (proportional to rotor speed), and power. Strip

chart recorders were equipped with event markers which were triggered

by contacting anemometers to provide current wind data simultaneously

with the electrical output.

It was decided that all parameters to be measured would be con-

verted to a voltage signal to permit easy transmission and scaling,

and to facilitate interfacing with standard recording instruments. A

data logger may be used in future research which makes signal condi-

tioning even more important. Figure l3 is the schematic of the

electrical output signal conditioning circuits. Generator voltage was

divided by lOO0 through a resistance network. A direct readout was

provided by a jl99 mV digital panel meter (DPM) and the millivolt

signal was also recorded on a strip chart recorder. Generator current

was passed through a 0.00l OHM shunt to provide a voltage signal of

l mV per Amp. Again, this signal was displayed on a j]99 mV DPM

and recorded on a strip chart recorder. The frequency of the windmill

alternator was measured using a Beckman frequency counter.FA

parallel

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30

system using a Teledyne Philbrick frequency-to-voltage converter (F/V)

was employed for a short period of time but failed after the test

cases using the resistive load. The output of the F/V was a millivolt

level signal that was proportional to the frequency of the generator.

The rotor RPM can be obtained by multiplying the frequency by l.82

(Fig. Al). This number is obtained in the following manner:

RPM = (f)(gear ratio)(2/alternator poles)(60 s/min) (ll)u

RPM = (f)(l/4.l2)(2/l6)(60)

RPM = l.82 f

Measuring power required several steps. The mV level voltage and

current signals were amplified and multiplied (Fig. l4) by an EAI TR-20

Analog Computer to provide a signal of l mV per watt. This signal was

recorded on a strip chart recorder to provide a continuous power record

and was input to a Wavetek Model lll Voltage Controlled Generator (VCG).

The frequency of the output signal of the VCG was thus proportional to

the power produced. This signal was counted on a Beckman Digital

Counter, providing a total count which, when divided by time, was

proportional to kw—h produced. During system calibration, this method

of measuring power was found to be inaccurate (App. E) and was not used

in the test cases. Alternatively, voltage and current values from the

recorder were multiplied together to produce power data.

Mind Measurement System

Two types of commercially-available anemometers were used to

monitor wind velocity at the test site. The Stewart anemometer is a

xx

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32I

small, lightweight, inexpensive cup anemometer that utilizes a

magnetic reed switch to measure the passage of 27 m (l/60 mile) of

wind. The Belfort anemometer is a slightly larger, heavier, and more

expensive cup anemometer that utilizes mechanical contacts to measure

27 m (l/60 mile) of wind. Although the Belfort model is more sophisti-

cated and has higher quality components, the contacts tend to pit and

must be cleaned and adjusted every 60 - 90 days. The Stewart anemo-

meters are virtually maintenance free and have not failed to operate

' satisfactorily.

Although wind units of 27 m (l/60 mile) are satisfactory for ob-

taining mean wind information and comparing various sites, that

distance represents a relatively long time (approximately 3 s duration

at a velocity of 9 m/s (20 mile/h)) and does not provide meaningful

short term wind velocity data.

0ne Stewart anemometer was modified to provide better resolution.

The worm and gear were removed and the actuating magnet was mounted

on the rotor shaft. Figures l5 and l6 show a Stewart anemometer and

the modification. This arrangement provides l6 times better resolution

(l.68 m (5.5 ft)).

· The recorders sold with the anemometers are of two types. The

Stewart odometer is a transitorized, electro—mechanical counter that

accumulates total elapsed distance. By dividing by the time between

observations one obtains an average wind speed. The Belfort instruments

are Rustrak recorders that have been modified to register the contact

closings of the anemometer. This recorder permits determination of wind

35

I

velocity over periods as small as l5 minutes duration. A transistorized

switching circuit was designed and added to the Belfort recorders to

allow their use with the Stewart anemometers. This circuit, Fig. l7,

protects the delicate reed switches from a large current flow from the

recorder.

Both types of recorders were used for site selection, in a remote,

outdoor environment. During cold, wet weather the Stewart odometer

tended to stick and the battery drain on both the odometers and the

recorders was excessive. These problems led to development of a solid-

state odometer using CMOS and TTL integrated circuit components,

Fig. l8. Figure l9 shows the completed counter. A second unit is

being developed using lOO per cent CMOS logic components for which the

battery drain will be negligible.

A Although mean value wind data is useful for initial wind energy

site surveys, the total available wind energy can only be determined

from a wind speed duration curve, which shows the amount of time the

wind speed was above a specified level.

Two sites may have an identical mean wind speed but have vastly

different potential for driving wind energy systems. Suppose for

example that two sites each have a mean wind speed of 4.5 m/s (lO

mile/h). The wind at Site A is 9 m/s (20 mile/h) during half the time

and calm during half the time. The wind at Site B is constant at 4.5

m/s (lO mile/h). From equations (2) and (3) the energy in the wind is

E = %pAzvj (12)

· 36 °

Contacting Anemometer‘

6 —l2V

In 'lK

· ——-<o+l2V _

· Input

HEP G 6GG5

Belfort Recorder

Figure·l7. Belfort Recorder Input Modification.

. 6 37‘.

620 .- _ _ . +6 _

660-1(TO) .ISPLAY ‘ • ‘ •

·6 BW74648 74648 746480660060 0660060 0660060

•/•

+6Display Switch· nnununnnq nurTo Pin l4

of Next74690 · · · ···— 4 · · 4 ·

·~$—

S MO*@ 74690 74690 74690 746692tages _ DEC^DE COUNTER , , 066006 COUNTER _ DECADE COUNTER + 6 ,‘ anunur inn ‘‘¤¤•¤¤v

‘•¤•unuuun eg.To Pin 2 of _ ' , _ _0606 74690 ’

+5+5 .

220 J —+6 4 106 +6 _ +6 +6 _

· I_ _ , , ¤u||¤|I•¤¤||• , g +50000610066 Zero Reset00611v180A100 +74122 74604 74674, NVERT,R _ 0 66,6 60- ,hd I |,

V 'if

lK I+5

Figure l8. Schematic of Integrated Circuit Odometer.

— 39

ThusEA

= äp/T(’¤/2)(9)3+%¤^(t/2)(¤)3 (T3)

and

EB = ·g—pA(t)(4.5)3 ° (T4)

Therefore

Q = (O.5)(9)3 = 4 (44)E6 (4.6):* ·

This effect is most noticeable when comparing sites that have

different geographical features or weather patterns. For example, a

coastal location may exhibit a strong diurnal variation while an inland

site may have fairly uniform wind speed characteristics throughout the

day, changing with the passage of weather fronts.

Reed [7] proposes that a sample duration of T5 seconds is an

adequate time period for obtaining wind speed samples. This time]

period can easily be handled by interfacing the solid state counter to

a microprocessor. There are devices on the market which will auto-

matically log wind speed-duration data, and at least one battery

operated device to accomplish this is being developed.

X. DATA4

—

Performance measurements for l3 separate test cases are recorded

in this section. Cases l through 7 document the use of the WVG-l20G

wind turbine to directly power a resistive load, with the load size and

switching level being changed between test cases. The last 6 cases

are concerned with the use of the windmill to charge the battery bank.

The state of charge was the primary variable between cases in these

. tests. A

Table 2 identifies the l3 test cases. Table 3 is a performance

data summary which includes the standard deviations of the measured

variables. The data for each test case are plotted against wind

speed in Figs. 20-32.

40

_ 41

ITab1e 2

I

Performance Test Case Identification

Case Date Load Description (Note)

1 8/5/77 Resistive, DL = 0.01 L1 = 0.1 L2 = 0.5Load Switching Re1ay Set at 120 V

2 8/6/77 Resistive, DL = 0.11 L1 a 0.1 L2 = 0.5Load Switching Re1ay Set at 135 V

3 8/6/77 Resistive, DL = 0.1 L1 = 0.1 L2 = 0.5Load Switching Re1ay Set at 135 V

4 8/6/77 Resistive, DL = 0.01 L1 = 0.1 L2 = 0.5Load Switching Re1ay Set at 120 V

5 8/6/77 Resistive, DL = 0.11 L1 = 0.1 L2 = 0.5‘ Load Switching Re1ay Set at 120 V

6 8/6/77 Resistive, DL + L1 = 0-2 L2 = 0-5Load Switching Re1ay Set at 120 V

7 8/17/77 Battery, 92 Ce11s, 129 - 140 V

8 8/23/77 Battery, 91 Ce11s, 120 V

9 8/23/77 Battery, 91 Ce11s, 121 V

10 8/24/77 Battery, 91 Ce11s, 123 — 126 V‘

11 8/24/77 Battery, 91 Ce11s, 130 - 137 V

12 8/24/77 Battery, 91 Ce11s, 135 - 136 V

13 8/24/77 Battery, 91 Ce11s, 135 - 138 V

Note: Resistive 1oads stated in fraction of generator rated output.

42 _

Table 3U

·

Performance Data Summary(Mean Value/Standard Deviation)

Case wind Occurrences Voltage Current Power Tip SpeedNo. m/s(mile/h) V A w Ratio

V l 2.7(6) l5 86/l8 .4/.l 3]/l3 8.]/2.63.6(8) 65 l06/l5 .6/.8 60/93 7.2/.84.5(l0) 20 l]4/7 2.2/2.2 255/253 6.4/.6

2 2.7(6) 5 .24/5 l.3/.2 32/ll 4.0/.43.6(8) 25 3]/6 l.6/.3 52/l9 3.3/.44.5(l0) 40 49/8 2.4/.3 l2l/37 3.5/.35.4(l2) 25 7l/l5 3.5/.5 255/85 3.7/.]6.3(l4) 5 70/]0 3.4/.5 240/72 3.]/.4

3 3.6(8) 5 38/5 _ l.7/.l 64/l3 3.8/.34.5(l0) 20 67/27 2.9/.9 22]/l57 4.4/].05.4(l2) 25 89/25 4.0/].7 384/275 4.3/l.l6.3(l4) 35 lll/l9 5.2/].9 599/307 4.4/.67.2(l6) l5 l25/9 7.0/2.5 887/364 4.l/.3

4 3.6(8) 35 99/l9 l.l/l.3 ll6/l47 7.0/.74.5(l0§ 40 l08/8 2.6/2.2 32]/269 5.7/].] ‘

5.4(l2 20 l07/6 3.7/2.2 397/245 5.0/.46.3(l4) 5 l09/6 4.3/2.0 476/226 4.3/.3

5 5 l7/2 ].0/.0 l7/2 3.2/.23.6(8 30 4l/l9 ].7/.9 88/89 3.8/].]4.5(l0) 45 54/ll 2.6/.4 l45/56 3.7/.55.4(l2) l0 85/22 4.5/2.0 4l7/303 8.]/.86.3(l4) l0 72/8 3.6/.3 265/44 3.l/.2

6 2.7(6) 5 l8/4 l.4/.4 25/l3 3.8/.63.6(8) l0 l9/3 l.7/.3 32/ll 2.7/.24.5(l0) 40 25/6 2.0/.5 53/23 2.5/.5 ‘

5.4(l2) 40 37/4 3.]/.3 l]5/27 2.5/.46.3(l4) 5 · 44/l 3.9/.] l7l/7 2.5/.l

7 2.3(5) 'l l29/— .0/- .0/-2.7(6) 3 l3l/l .0/.] 4/73.l(7) 8 l3l/l l.0/.7 l3l/873.6(8) 22 l3l/l l.3/.6 l68/734.l(9) 29 l3l/2 2.9/.9 369/l27 »4.5(l0) 37 ]33/3 4.4/].3 589/l744.9(]]) 3l ]34/2 5.7/].3 765/]74

43

Case wind Occurrences Vo1tage Current Power Tip SpeedNo. m/s(mi1e/h) V A N Ratio 1

° 7 5.4(12) 22 136/2 _ 8.2/1.2 1114/170_ 5.9(13) 17 137/2 9.2/1.3 1267/173

6.3(14) 11 137/1 10.2/.9 1399/1376.7(15) 3 138/0 12.5/.2 1725/247.2(16) 1 139/- 15.3/- 2127/-7.7(17) 1 140/- 15.3/- 2142/-

8 2.7(6) 1 120/- .3/- 36/- 9.7/-3.1(7) 4

”120/0 1.0/.4 125/47 8.7/.4

3.6(8) 7 _120/0 1.5/.4 175/49 7.9/.3I 4.1(9) 11 120/0 2.7/.5 327/61 7.3/.2

4.5(10) 6 120/0 3.5/.4 416/44 6.7/.14.9(11) 1 120/- 4.8/- 576/- 6.1/-

9 1.8(4) 2 121/0 0/0 0/0 9.5/02.3(5) 6 121/0 .1/.2 10/25 9.2/.92.7(6) 4 121/0 .1/.3 15/31 8.6/.93.1(7) 6 121/O' .7/.9 89/109 8.3/.73.6(8) 7 121/0 1.2/.6 126/56 7.8/.34.1(9) 4 121/0 3.0/.2 363/247 7.5/0

10 . 3.1(7) 1 123/- .4/- 49/- 7.8/-3.6(8) 2 125/2 1.1/.6 131/80 8.0/.44.1(9) 4 124/1 1.2/.8 146/96 6.9/.54.5(10) 6 123/1 2.6/.8 319/93 6.7/1.34.9(11) 7 123/1 4.2/.6 479/48 6.3/.15.4(12) 8 124/1 4.8/.8 590/95 5.7/.25.9(13) 3 124/2 5.9/.1 728/46 5.5/.16.3(14) 2 125/0 · 6.9/.2 869/26 5.1/.26.7(15) 5 125/1 7.4/.6 922/80 4.8/.17.2(16) 2 126/0 8.1/.1 1019/8 4.7/.1

11 3.1(7) 2 130/0 .6/.2 71/28 7.9/1.23.6(8) 3 131/1 .3/.3 52/37 7.9/.34.1(9) 1 130/- .5/- 65/- 7.2/-4.5(10) 3 133/3 1.9/.5 251/68 7.1/.14.9(11) 2 133/0 5.8/2.4 771/320 6.7/05.4(12) 1 135/- 5.5/- 743/- 6.3/-5.9(13) 5_ 135/1 6.0/1.1 807/145 5.8/1.26.3(14) 06.7(15) 2 135/1 7.9/1.3 1062/165 5.3/.77.2(16) 0 ‘

7.7(17) 0. 8.1(18) 1 137/- 12.0/- 1644/- 4.5/-

’44

Case wind Occurrences Vo1tage Current Power Tip SpeedNo. m/s(mi1e/h) V A w Ratio

12 4.5(10) 2 135/0 3.0/0.6 405/96 7.1/.24.9(11) 5 135/0 4.1/1.1 556/150 6.7/.25.4(12) 3 135/1 4.8/.7 642/104 6.3/.15.9(13) 2 135/1 5.4/1.6 733/214 5.9/.16.3(14) 1 136/- 6.1/- 830/- 5.5/-

13 3.6(8) 1 135/- 1.8/- 243/- _9.0/-4.1(9) 0

‘

4.5(10) 1 136/- 3.1/- 422/- 7.4/- ·4.9(11) 2 .136/0 3.7/1.3 503/173 6.8/.15.4(12) 1 135/- 3.9/- 527/- 6.1/-5.9(13) 1 136/- 5.3/- 721/- 5.8/-6.3(14) 2 137/0 7.1/1 966/10 5.6/06.7(15) 1 137/- 6.8/- 932/- 5.3/-7.2(16) 1 138/- 8.7/- 1201/- 5.0/-

45

Key: U V, Vo1tage, V

O I, Current, A

O X, Tip Speed Ratio, QR/Vw

150 A P, Power, kw 20

2.5 100 /2 I 10V

2.0 60 0 10

81.5 0 .

-6

1.0 _ X

4

0.5”

2

0.0 0.9 2.7 4.5 6.3 8.0(2) (6) (18) (14) (18)

windspeed, m/s (mi1e/h)

Figure 20. Performance Data, Case 1.

46

Key: g V, Voltage, V

O I, Current, A

O X, Tip Speed Ratio, QR/Vo,

V50 A P, Power, kw 20 I

2.5 100 I l0

V E2.0 60 0 l0

81.6OP

6l.0 _x

4O

0.52

A .

0.0 A Q.9 2.7 4.5 6.3 8.0(2) (6) (TO) (T4) (T8)

windspeed, m/s (mile/h)

Figure 2l. Performance Data, Case 2.

47

Key: D V, Vo1tage, V

°I, Current, A

O X, Tip Speed Ratio, QR/Vw

. 150 A P, Power, kw 20 I

2.5 100 1 10

v .

2.0 50 0 10

81.5 0

p 6

1.0I

_XWO4

0.52

0.0 0.9 2.7 4.5 6.3 8.0(2) (6) (10) (14) (10) 4

windspeed, m/s (mi1e/h)

Figure 22. Performance Data, Case 3.

48

Key; Q V, Voltage, V

· ¤ I, Current, A(

O X, Tip Speed Ratio, QR/Vo.,

_ l50 A P, Power, kN 20‘

2.5 l00 I l0

V2.050 0 l0

8. l.5 0

. p I 6

l.0 IX

4

0.6 A2 .

A

0.00.

.9 2.7 4.5 6.3 8.0(2) (6) (TO) (T4) (T8)

Hindspeed, m/s (mile/h)

Figure 23. Performance Data, Case 4.

° 49

Key: D V, Vo1tage, V‘

°I, Current, A

· () X, Tip Speed Ratio, QR/V„

150 4; P, Power, kw 20

2.5 100 I 10

CJ

V E] 1

2.0 60 0 10

81.5 0

P 6

1.0 ‘ _ XC;""£>___,E;-·'(>———„, 4O

0.5„ A 2

_ A

0.0 0

.9 2.7 4.5 6.3 8.0(2) (6) (10) (14) . (18)

Awindspeed, m/s (mi1e/h)

Figure 24. Performance Data, Case 5.

50

Key: EI V, Vo1tage, V‘

°I, Current, A

O X, Tip Speed Ratio, QR/V„,

150 A P, Power, kw 20

2.5 100 I 10

V0000 0 108

1.5 0 ·

P 6

1.0 IX

I 4

0.62

0.0 05

.9 2.6 4.5 6.3 8.0(2) (6) (10) (14) (18)

_ Nindspeed, m/s (mi1e/h)

Figure 25. Performance Data, Case 6.

I 51

Key: ¤. V, Vo1tage, V

°

I', Current, A

A P, Power, kw

150 290

| . .¤

Ü ¤ ¤- -

l B

: O

0

2.5 100 , ° I 10O

•V 0.

0 A A• 0

2.0 : 60 „·

9 19

A

81.5 0 ' _

A

P‘

6A3

1.0A

4

A0.5

Z5 2,

A A

O_0 A„4$ O.9 2.7 4.5 6.3 8.0(2) (6) (1:0) (14) (18)

windspeed, m/s (mi1e/h)

Figure 26. Performance Data, Case 7.

52

Key: :1 V, Vo1tage, V

O I, Current, A

O X, Tip Speed Ratio, QR/V„

150 A P,‘1¤¤we¤~, kw 20

l I I g g.‘: ‘

•2.5 100 ° ° I 10V

g_g 0 O .100

O

Q 8

1.5 |O

O

P • 6l

1.0 1X

4

A0.5

A

AA

0.0 ^ Q.9 2.7 4.5 6.3 8.0(2) (6) (10) (14) (18)

windspeed, m/s (mi1e/h)

Figure 27. Performance Data, Case 8.

53

Key; III V, Vo1tage, V

°I, Current, A 1

O X, Tip Speed Ratio, QR/Vw

_ _ 150 A P, Power, kw 202.5 100 I igV .

2.0 60 0 100 .

_

OO 8

1 1.5 0•

1,0 0x

_ 4

0.5u

A 2

. A Al

0.0 0_ .9 2.7 4.5 6.3 8.0

(2) (6) (10) (14) (18)windspeed, m/s (mi1e/h)

Figure 28. Performance Data, Case 9.

54

Key; ¤ V, Voltage, V

¤ I, Current, A

O X, Tip Speed Ratio,

A P, Power, kw 29

I'

I u g l I'

!'

2.5 100 I l0

7 V2.060 ,0 l0

8O O

l.5 OI

OI 6

. A1.0• . O _><‘

4A

A

O•5 A

2A

A A

0.0‘ 0

.9 2.7 4.5 6.3 8.0(2) (6) (l0) (l4) (l8) ,

windspeed, m/s (mile/h) I

Figure 29. Performance Data, Case l0.

55

Key; g V, Vo1tage, V V

O I, Current, A _'

O X, Tip Speed Ratio, QR/Vw _

150 A P, Power, kw 20N

.· -

I I I '*| .

. 2.5 100 10 ‘•

I

V•

2.0 60 °•

° 0 io

• • 8, 1.5 •

-

P O„ • °

\

1.0 . x—

A AA 4

0.5’

2

A

A0.0 0

.9 2.7 4.5 6.3 8.0(2) (6) (10) (14) (18)

windspeed, m/s (mi1e/h)

Figure 30. Performance Data, Case 11.

56

Key. 5 V, Vo1tage,V

9 I, Current, A

C} X, Tip Speed Ratio, QR/V„ -I

150 [5 P, Power, kw 20E}-{}—{}-{}-{J

2.5 100 I 10 .

2.0 60 0 108

1.5 00

0O

P• 6

01.0 _X

A

0.52

0.0 0.9 2.7 4.5 6.3 8.0(2) (6) (10) (14) (18)

windspeed, m/s (mi1e/h)

Figure 31. Performance Data, Case 12.‘

‘ 57

Key: ¤ V, Vo1tage, V

O I, Current, A

AC} X, Tip Speed Ratio, QR/Vw

15Ü A P, POWGT, KN202.5

100 I 10O

V

2.0 50 0 10I

.

81.5 0

_6

P _A

1.0 A >X

4

0.5A

2

0.0 1 6 0.9 2.7 4.5 6.3 8.0(2) (6) (10) (14) (18)

windspeed, m/s (mi1e/h)

Figure 32. Performance Data, Case 13.

XI. DISCUSSION

Interpretation of Data

Figures 33 and 34 are mean power curves vs. wind for the resistive_

. load tests and the battery load tests respectively. The ideal power

curve is also plotted for reference.

The first observation that one can make after examining the dataI

is that the windmill extracts more power from the wind when connected

to the battery bank than when directly powering the resistive load.

The second observation is that the windmill operates at higher tip

speed ratios when used with a battery load. The reason for this is

that when the alternator voltage falls below the battery voltage, the

alternator is_unloaded and the windmill is "free-wheeling“. This is

evidenced by the fact that the tip speed ratio is high at low wind

speeds and decreases as enough voltage is generated to charge the

batteries. The tip speed ratio for the resistive load tests does not

have a consistent identifying characteristic. —

Table 4 lists the mean power output, power coefficient, and tip

speed ratio for the resistive loads and the battery load, for each

observed wind speed. Note that values of Ep above 0.20 correspond to‘

tip speed ratios of between 6.l and 7.2. This observation confirms the

importance of maintaining the windmill blades at a good angle of

attack. However, even the highest value of Cp obtained corresponds to

an efficiency of only 39 per cent. _

Manufacturer's data was not supplied for the wVG—l20G wind turbine

and comparison with Fig. B-l is not possible as most of the data was

58 °

59

3.0 1V

2.8

2.6

2.4

2.2

2.0

1.8' (Idea1)

1.6 -

1.4 - /( /-, 1.22 ./ 1· /

ä 1.0 ~ /S .8 8 A ’ V

.6 ·A

- .4A

.2. · ^4—$

.9 2.7 ‘ 4.5 6.3 8.0(2) (6) _· (10) (14) (18)

wind Speed, m/s (miie/h)

Figure 33. Mean Power Output Curve, Resistive Load.

60

(3.0 ·

2.8

2.6 „2.4 6

2.2 [

2 0/

1 ‘ / .1.6 - ' /

1,5 (Idea1) . A/

T.4 ·

T.2EE

‘ ‘ A1.0 A. ä [Ä

Ü- •8 A ‘A.6 lx

•4 AA

.2.A

A

I_g 2.7 4.5 6.3 8.0(2) (6) (TO) (T4) (18)

Mind Speed, m/s (miTe/h)

Figure 34 . Mean Power Output Curve, Battery Load.

61

Tab1e 4

Power Output Summary (Note)

Battery Load Resistive Load

Vw I IP op Cp X P op Cp° Xm/s (mi1e/h) w w kw kw

2.2 '(5) 9 0 0.05 9.2 _

2.7 (6) 18 9 0.05 9.1 27 6 0.07 4.8

3.1 I (7) 89 23 0.15 8.2

3.6 (8) 131 46 0.15 8.1 73 25 0.09 4.7

4.0 (9) 271 89 0.22 7.2 I

4.5 (10) 337 62 0.20 .7.0 132 64 0.08 4.4

4.9 (11) 518 88 0.23 6.5

5.4 (12) 579 47 0.20 6.1 258 120 0.09 4.7

5.8 (13) 726 39 0.19 5.7

6.3 (14) 855 59 0.18 5.4 444 168 0.09 3.5u

6.7 (15) 910 61 0.16 5.1I

7.2 (16) 1026 100 0.14 4.9 842 - 0.12 4.1

7.6 (17) I8.0 (18) 1562 - 0.16 4.5

NOTE: P Average Power Output

cp Standard Deviation of PowerCP Average Power Coefficient

X Average Tip Speed Ratio

Va1ues of P, op, and CP are adjusted using the correction

factor of 0.95 ca1cu1ated in Appendix F.

62

obtained with the rotor running be1ow 100 RPM. Because of the 1ack

of comparative data it is necessary to make some assumptions con-”

cerning the cause of the 1ow efficiency. If the gear train and

a1ternator are assumed to have a combined efficiency of 0.70, and if

misce11aneous system 1osses are assumed to be no greater than 0.10,

the aerodynamic efficiency must be on1y approximate1y 0-62- This may

be due to the poor profi1e (Fig. 8) which cou1d 1ead to ear1y separa-

tion and sta11. The even 1ower efficiency obtained with the resistive

1oad is thought to be due to the resistive 1oad preventing the system

from reaching optimum rotationa1 speed (average tip speed ratio for

resistive 1oad was 4.4), causing most of the b1ade to be at a high

ang1e of attack (Fig. 10). In gusty conditions it was noticed that

~ the resistive 1oad tended to brake the rotor during 1u11s and that

during a gust the rotor had to be acce1erated to operating speed. The

un1oading effect of a battery 1oad he1ps to maintain a higher and

more uniform rotor speed.

Load Switching and Sizing6

A wind turbine system that cou1d efficient1y power a resistive

1oad bank wou1d be idea1 to use as supp1ementary heating. It is

be1ieved that reducing the incrementa1 1oad size to 1/15 the rated -

capacity wou1d a11ow the windmi11 to operate with an effective tip

speed ratio. It is envisioned that a 1oad segmented at 1/15, 2/15,

4/15, 8/15 cou1d be switched easi1y emp1oying a comparator circuit

with a binary output using on1y 4 switching SCR's. Such a circuit

A 63

would be much more effective than the 3—level switching now employed.

The cost of semi—conductor switching vs. the relays and contactors of

the Electro system is estimated to be much lower.

A Battery or Direct Load

Although these tests show that a battery load allows the wind

turbine to operate with higher efficiency, it must be remembered that

. only 54 - 60 per cent of the energy put into the battery will be”

recovered. This fact makes the overall performance of the resistive

load comparable to that of the batteries. Thus it would appear that «

for optimum performance some sort of composite system is necessary.

Power from the windmill would be directly used by the system, while a

small battery bank would be used to store excess energy that the

electrical system cannot use, and would be a reserve used during motor

starting and in calm periods. A control system to accomplish this is

being designed for use with the wVG—l20G and the refrigeration system

described by Blanton [T3].

IPower Multiplier Integrator

Although the cause of the inaccuracy of the power multiplier

circuit was not discovered before the system was moved, it is believed

that the idea is a sound one and should be explored further to enable

automatic power recording. Integrated circuit devices are available

which can replace all the functions used on the analog computer and

the voltage controlled generator.

XII. CONCLUSIONS

1. Power produced by the E1ectro wVG—120G wind generator was measured

for wind speeds in the range of 2 - 8 m/s (4 — 18 mi1e/h), using

both a resistive 1oad and a battery 1oad. Output power varied

from 0 to 1.6 kw for these wind speeds.

2. The power output using the resistive 1oads varied about 37 per cent

for a given wind speed, showing the dependence of performance on

1oad sizing and switching. By comparison, using the battery

1oad, measured power output varied on1y about 20 per cent at a

given wind speed.‘

3. The power coefficient varied from 0.05 to 0.23, and appeared to

be dependent on the tip speed ratio. The highest va1ue of CP was

obtained at a tip speed ratio of 6.5.

64

XIII. RECOMMENDATIONS FOR FURTHER RESEARCH

l. Conduct further performance evaluation at wind speeds of 7—l8 m/s

(l5 — 40 mile/h).

2. Investigate all means to optimally "tune" the wind turbine:

Calibrate the alternator in a test rig.

Dynamically balance the rotor.

Improve the airfoil and twist of the blades.

3. The use of a data logger is recomnended to enable more precise

measurements, along with the capability of direct transfer of

data to the VPI&SU computer system.

4. Develop a better switching system for direct heating.

5. Develop on—rotor instrumentation to measure air pressures and

blade stresses. iI

65I

» XIV. LITERATURE CITED

1. Schetz, J. A., W. O'Brien, H. Moses, T. Weishaar, and D. Vaughan,‘ A lication of Windmills to A le Coolin and Stora e, Progress

Report for the Period November 1976 - February 1977, VirginiaPolytechnic Institute and State University, 1977.

2. Putnam, Palmer Cosslett, Power From the Wind, Van NostrandReinhold Company, New York, 1948.

3. Walter, Samuel, "Briefing the Record", Mechanical Engineering,August 1977, p. 45.

4. Westh, H. Claudi, "A Comparison of Wind Turbine Generators",Proceedings of the Second Workshop on Wind Energy ConversionSystems, Washington, D.C., 1975.

5. Rueth, Nancy, "Energyscope", Mechanical Engineering, August 1977,p. 19.

6. Liljedahl, L. A., "Wind Energy Use in Rural and Remote Areas",Proceedings of the Second Workshop on Wind Energy ConversionSystems, Washington, D.C., 1975.

7. Wilson, R. E., "Applied Aerodynamics of Wind Power Machines",Proceedings of the Second Workshop on Wind Energy ConversionSystems, Washington, D.C., 1975.

8. Wilson, R. E., and P. B. S. Lissaman, Applied Aerodynamics ofWind Power Machines, Oregon State University, Corvallis, Or.,1974.

9. Oman, R. A., and K. M. Foreman, "Cost Effective Diffuser1

Augmentation of Wind Turbine Power Generators", Proceedings ofthe Second Workshop on Wind Energy Conversion Systems,Washington, D.C., 1975.

10. Smulders, P. T., "Physical Aspects of Windmill Design", Physicsin Technology, September, 1976. g

- ll. Zlotnik, M., "Energy Storage for Wind Energy Conversion Systems",Proceedings of the Second Workshop on Wind Energy ConversionSystems, Washington, D.C., 1975.

12. Blanton, J. C., "Design of a Wind — Powered Cooling System foran Apple Storage Facility", M.S. Thesis, Virginia PolytechnicInstitute and State University, 1977.

66

67‘

l3. Neick, F. E., Aircraft Progeller Design, McGraw-Hill, New York,l930.

l4. Electro, GmbH, Operating Manual for wVG—l2OG, Ninterhur,Switzerland. .

l5. Holman, J. P., Exgerimental Methods for Engineers, McGraw-Hill,New York, l97l.

XV. APPENDICES

68

69

Appendik A

Specifications of Electro WVG-120G —

70

Table A—l

Specifications of Electro

wVG-l20G wind Generator

Rated Output lO kw

Output Voltage ll0 V (3-Phase A. C.)

Frequency Range 50-T30 Hz

Propeller Speed Range l0O — 250 RPM

I Number of Propeller Blades 3

Field Regulation Combination of 2 permanentmagnets and 2 field rotor °

_sections _

Field Current l.2 - l.5 AI

Field Voltage)

. 50 - 80 V

Generator weight 2795 N (628 LBF)

7]

G4-*

¢‘

G 3 N

. I1 ”· ‘é°GJ <'

L L r-

g$5

G)o U $1

GJLGJ'4-GJIZ

© äGQ Q LIC N LL-

~.¢

V)U

-1-4-*

O snOO ••··1- L_ GJ

4-*N U:1: E ru

G Q. L-00 cz rc

>q ..CU . C) •~ Q -C LD 'UGJ Ii GJ L3 ^ GJ OG' Q. 4-*cu V7 r¤L L

LL. L GJO C4-* GJ

G O (D¤'1-

1-<GJ• S-

kD 3C7

(D -1-N L1.1-

GCD

‘ 1-V Z],U3J.A|"I:)

• O O G G G<' G N KD <' N

IC

G CO LD <' N1-·

Mq ‘4aM0d

72

E Appendix B

Electrical Schematics of Electro wVG—l2OG

73

Table B—l

Electrical Schematic Legend

SAB Control Switch Limiter

SSp Voltage Limiter

c Spark Discharge Capacitor

R Resistors

SpKP Voltage Control Potentiometer

ES Limit Switch for Brake

SM Control Motor V

Sch Collector Ring ·

VMS Voltmeter Switch

Si Main Fuse3

V Voltmeter

A Ammeterl ·

MK Ground Terminal

Q Insulated Terminal

I Diode Switch for l0 - 40 V

II Diode Switch for 40 - l20 V

3 Current Carrying Lead for Automatic Control

4 wind Pressure Switch Lead _8 Starting Circuit Lead

SJB Starting Relay

dl,d2 Relay type MK2, 24 V DC

cl,c2 Load Contactor

74

Au

Load Carrying Lead

B Contactor Switching Relay Lead

CA Contactor Switching Relay Capacitor

R,S,T 3-Phase Leads

F Field winding

ZL Zener Diode Switch ·

I75I"-

I pot .

I$1111 II I_I° I I

IS!

I• ‘I l 1

1 · •' 1.5 1T

SCH (II? I " 1; SABIIc DI Z I 1 j

111ind Pressure

1

I.

I A S1 6611 -I

I vmsI I I•

1 Q I1 C IL A..

II

1

ssp II1 C 1. — 6.111 II ST I

1 I

SJI1 11 ' 1”—I

...1-- ... .--.-..--..- ..---.-11c 1 1 I______-- 1 - ----.-.. .. J I

Figure B1. wVG—12OG Contro1 Circuit.(From Reference 14) _

- _ 76 ·

A I

I_ - Load-Contactor Bgard - E · I . ·

_ I

A I Dc HOJGO V Direct Load

B .V

II .

' CAC CI . I

\D] • · ß 1rin; -—I-I · c

II _ •

.ILoad ICA C

I

c C2D2 • . !¤

VI

IWIIA - -- , C I' • • _ „ gl |

'-

IC Load 2 I

. Figure B2. wVG—I20G Load Contactor Board. V„ (From Reference I4) A 1

77

Appendix C

Resistive Load Calibration Data ·

U? G C) O1 N N LDN r- N N (Ü T LD-4

T O C) O3 Q N LDN I3 N N (Ü T LO—I .

(Ü G ON O3 N N KO| • • • • • •

N I3 1- N (Ü T LD....!

CT! CD O O Q Q LON r- N (Ü (Ü T LD.-I

U')4-* ¢N I3 O O 05 Q IN I-Og ( | • • • • • •

GJN-’

N I3 N N (Ü T LOE -1GJ 4-II3 CL1.! G)

1·- S-1 cu L M O cx ox N N no

(_) > 3 | „ • •-

• ••1- C.) I3 I3 1—· N (Ü T LD

G) -I-I ..1I3 (D ..Q -1-(U (/7I- (DDt C}! O O3 O1 Q IN LO

3 I3 r-· 1- N (Ö T LD.-I

GCDG1- I3 Ö ON CY Q N LO

| • • • • • •

1- r··I3 N (Ü T LD

_ _!

IN OW OW Q N KD

| • • • • • • ·.J 1- 1- N (Ü T LO

1- OW O'! Q N LO LD| • • • • • • _

..! G •·- N (Ü T LD2

(UC7ggrx-I-’>

LD G LO G I-O Ö·‘

1-N-# N LD N O N LOg I3 1- I3

-U1 C

‘

+> <u«·~ ao M cw no N 00C S-{

• • • • • •

(U P P (\| F') G')E 3

•

GJ L) LDr-LLJ 'U

GJ C3 U1 fü

fü*" ,‘ O 4-*> LO O LD LD O ·

'•

O•-•\-/ GI LD N O (\| LD ¢'

KD O P P r-> ux

(NIV74.) veC P

-

E GJGJ thr- füLLJ — U A

(U GJ +9l' >

IhLJ ·r· CU

4-*+9

G) V7u- ·r- :.Q th

•r-

fü GJI'- CTIGJ .J4.)

·C

„ CS-

••-

GJ+9 'U

_ P GJU'}5

+9VI C N LO U)

·|-7 G)"‘ Gl C") (V) ¤' LO KD +9g gq • • • • • • g

‘

G) S--9 O O O O O C) GJE 5 E

_

GJ L) GJr- PLIJ GJ

GJ3 CD 3

ßrsO +-*> LD O LD O LO O OO r-~9 N LD r~ O N LO O•— Q

•— •-— P P>

GJ+9OZ

‘80

VAppendix D

Specifications of Modified Nife C360O Battery _

81 · V

‘ Table D-1Specifications of Modified Nife C3600 Battery

Manufacturer: Nife IncorporatedI

Model Number: C36OOCell Type: KB-12 Nickel Cadmium

Open Circuit Voltage: 1.33 - 1.35 V/Cell

Number of Cells: 91 in series

Rated Capacity: 123 A-h

Discharge Specifications:I

I Normal Rate 30A _Normal Time 4 h

I_

Initial Voltage 1.3 V/Cell g

Average Voltage 1.2 V/Cell

Final Voltage 1.0 V/Cell

Charge Specifications:

Maximum Constant Current Rate 34.6 A I

Time at Maximum Rate 5 h

Voltage at Maximum Rate 1.40 - 1.72 V/Cell‘

Maximum Constant Voltage Rate 1.55 V/Cell

Float Voltage (Trickle Charge) 1.42 V/Cell

82

_ Appendix E

Measurement System Calibration Data

83 V I

Table E-lV

Voltmeter Calibration Data .

Instrument: Veritas V-925 VOM

Date: August 9, l977

Conducted by: W. F. O‘Brien, Jr.

Standard: Twinco Calibrator

Voltage Actual QV} Voltage Indicated QV}

0-25 V DC

5.0 5

l0.0 9.8J

16.0 14.7 i20.0 l9.5

25.0 24.8

0-lO0 V 0C Vl0 · ll ·

30 30

50 49.5

l0O lO0

0-500 V DC

l00 lO0

200 l95

500 495 ·

84

Table E-2

Ammeter Calibration DataI

Instrument: weston Model 430 Ammeter, Serial No. 19991

Date: August 9, 1977

Conducted by: W. F. 0'Brien, Jr.

Standard: Twinco Calibrator

Current Actual {A} Current Indicated {A}

0-10 A DC

0.0 ° 0.03 · »

2.0 2.0

5.0 5.0 '

10.0 10.0

U 85

Table E—3

Electrical Measurement System Calibration Data (Note)

Instrument: Voltage Divider Circuit

Current Shunt

Hewlett Packard Model 4100 B Recorder ·

. EA1 TR-20 Analog Computer

Data: August 25, 1977

(

Conducted by: T. E. Benim

Standard: Veritas V-925 VOM

weston Model 430 Ammeter

Actual Actual Actual Recorded Recorded Recorded TR-20(

Voltage Current Power Voltage Current Power Displayed(V) (A) (kw) (V) (A) (kw) Power

' (Calculated) (kw)

‘ 0 0.0 0.0 0 0.0 0.0 0.025 0.9 0.023 25 1.0 0.025 0.050 1.9 0.095 50 2.0 0.100 0.075 2.8 0.210 73

’3.0 0.220 0.24

100 3.7 0.370 97 4.0 0.388 0.64125 4.5 0.563 121 4.9 0.593 1.2150 5.4 0.810 145 5.9 0.855 1.7‘ 0 0.0 0.0 0 0.0 0.0 0.0 .25 2.0 0.050 25 2.1 0.053 0.050 ~ 3.8 0.190 49 4.1 0.201 0.2475 5.7 0.427 73 6.2 0.453 0.86

100 7.5 0.750 96 8.0 0.768 1.7125 9.3 1.16 120 10.0 1.20 2.4150 11.0 1.65 144 12.0 1.73 3.4

(Note: Calibration performed using a DC power supply to simulatewindmill output.

86 _

Actual Actual Actual Recorded Recorded Recorded TR—20Voltage. Current Power Voltage Current Power Displayed

(V) (A) (kw) (V) (A) (kw) Power(Calculated)(kw)0

0.0 0.0 0 0.0 0.0 0.025 3.0 0.075 25 3.2 0.080 0.050 5.8 0.290 49 6.2 0.304 0.6575 8.6 0.645 72 9.3 0.670 1.6

100 11.3. 1.130 95 12.0 1.14 2.3125 ° 13.8 2.07 119 15.0 2.23 3.6150 16.5 2.47 144 18.0 2.59 5.2

0 0.0 0.0 0 0.0 _ 0.0 0.025 4.0 0.100 25 4.2 0.105 0.150 7.9 0.395 48 8.5 0.408 1.075 11.5 0.863 73 12.5 0.912 1.8

100 15.0 1.50 96 16.3 1.57 2.9125 18.3 2.29 120 20.0 2.40 5.0

0 0.0 0.0 0 0.0 0.0 0.025 5.0 0.125 24 5.4 0.130 - 0.2550 9.6 0.480 49 10.5 0.515 1.2575 13.3 0.998 72 15.5 1.12 2.0

100 18.5 1.85 95 20.0 1.90 4.0

87F

‘ Appendix FI

Undertainty Ana1ys1sI

88

Uncertainty°Ana1ysis

A11 instruments used in this thesis were ca1ibrated or checkedfor accuracy except for the osci11oscope and its time base which were

used as a reference in ca1ibrating the F/V converter, and the Beckman

counter. The resu1ts of the e1ectrica1 measurement system ca1ibrations

are tabu1ated in Appendix E. The resu1ts of tests on the other

instruments are discussed be1ow.The F/V system fai1ed before a documented ca1ibration cou1d be

performed but a pre1iminary operationa1 check using the VCG as a signa1

and the osci11oscope as a reference showed the accuracy to be within

j_0.02%. Simi1ar1y the frequency counter was accurate to within j_1

digit (j_1 Hz). .I

The Stewart anemometers were checked in the VPI&SU open throat

wind tunne1 and were found to be accurate within j_1 digit. For a

1 minute average this corresponds to j_O.5 m/sec (j_1 mi1e/h). Tests

with two recent1y purchased Stewart anemometers show that they

indicate about 1.3 - 1.8 m/s (3-4 mi1e/h) 1ow in the range from 6.7 —

1 17.9 m/Sec (15 - 40 mi1e/h)- However these tests were run in adifferent wind tunne1 and wind speeds be1ow 6.7 m/sec (15 mi1e/h)cou1d not be obtained. It is recomended that a11 anemometers used inthis project be ca1ibrated under identica1 conditions to obtain con-

sistent ca1ibration data. It was decided to assign an uncertainty to

the Stewart anemometers of j_.5 m/sec (1 mi1e/h) or j_10%, whicheveris greater. V

89

Correction factors and uncertainties were calculated using

the mean value of reading/actual values and the standard deviation

of these values. The results are:

VOM 1.00 j_0.03

Ammeter 1.00 j_0.03

Voltage Recorder 1.03 j_0.02 (Based on VOM)

Current Recorder 0.93 j_0.02 (Based on Ammeter)

A _ TR—2O Computed Power 0.59 j_0.8l (Based on VOM + Voltmeter)

Since the voltage and current recorders were calibrated using a

secondary source, the precision of these recorders was estimated using

a sum of squares technique outlined by Holman [15]. The uncertainty

of both the voltage measurement and the current measurement are equal

to: ‘2 2 l/2 AWI = WV = iI(wmeter) + (wrecorder) 1

U2 2 V2

= j[(0.03) + (0.02) ]

=» io.04

‘ The power calculated from the values of recorded voltage and

current was plotted and found to be linear, with true power equal to

0.95 times calculated power (0.93 x 1.03 = 0.95). The uncertainty is:

2 2 1/2Wp = i[(wV) + (WI) 1

2 2 1/2= ;*_[(0„04) + (0.04)]= ;0.06 A A

90

Simi1ar1y, for tip speed ratio:

‘2 2 T/2

l.

NX = :[(Wf) + (wvw) ]

2NX= j[(.02) + (.1)]

2NX = jp.] 2

and, for power coefficient:

2 . 2 1/2Ncp = j[(Np) + 3(NV ) ] = j0.18

. 91 E ‘

Appendix G

List of Equipment ·

. ‘ 92 _

Table G-l .

List of Equipment

Ammeter: weston Model 430

Analog Computer: EAI Model Tr-20

Anemometer: Belfort Model 5-349A Totalizing Anemometer

Stewart l/60th Mile Anemometer

Counter: Beckman Universal EPUT TimerI

Digital Panel Meter: Datel Model 2100 AV

Frequency to Voltage Converter: Teledyne Philbrick Model 4702

Oscilloscope: Tektronix Type 564 Storage OscilloscopeA

ITektronix Type 2A63 Differential Amplifier

Tektronix Type 2367 Time Base

' Recorder: Hewlett - Packard Model 7100 B Strip Chart Recorder

Mosely Model 7100 B Strip Chart Recorder

' Belfort Model 6081 Event Recorder

Voltage Controlled Generator: wavetek Model III

Voltmeters Veritas V 925 VOMV

PERFORMANCE MEASUREMENT

OF A TEN KILONATT

HORIZONTAL AXIS NIND TURBINE

by

Thomas E. Benim _ '

(ABSTRACT)

A system to measure the performance of a l0 kN horizontal axis

wind turbine was designed and was employed to test an Electro NVG-l20G

wind generator.

Parameters measured were wind speed, voltage, current, andI

frequency. Output power and tip speed ratio were calculated from the

measured parameters. A system to automatically calculate instantaneous

power and to integrate power was developed. An improved digital

anemometer odometer was designed and built.

Tests were performed with the windmill powering a resistive

heating load as well as charging a battery.