An Experiment on Power Properties in a Small-Scaled Wind Turbine Generator

doi:10.4236/jpee.2013.17002

Journal of Power and Energy Engineering, 2013, 1, 6-13

http://dx.doi.org/10.4236/jpee.2013.17002 Published Online December 2013 (http://www.scirp.org/journal/jpee)

An Experiment on Power Properties in a Small-Scaled

Wind Turbine Generator

Jee-Ho Kim, Hyun-Dai Yang , Kyu-Ji n Lee, Sung-Do Song, Sung-Hoon Park, Joong-Ho Shin

Department of Mechanical Design & Manufacturing, Changwon National University, Changwon 641-773, Korea.

Email: [email protected], [email protected]

Received September 2013

ABSTRACT

This study configures a simple wind tunnel using a blower for generating wind energy, which is equivalent to natural

wind, and a test system that measures properties of power. Also, the mechanical and electrical power in a small-scaled

wind turbine are empirically measured to analyze the relationship between the mechanical and electrical power.

Keywords: Small-Scal e d Wind Turbine; Vertical Axis Windmill; Gearbox; Mechanical Power; Electrical Power

1. Introduction

Environmental issues including ozone depletion have be-

come to the front because of exhausting natural resources

and carbon dioxide emissions according to sustainable

use of fossil fuels during industrialization processes. Al-

though there are some efforts that are starting to control

such carbon dioxide emissions based on UNFCCC, it is

not possible to fundamentally solve the energy depen-

dency of fos s i l fuels. Thus , s tudies on ne w a nd r enewable

energy have been largely conducted throughout t he world.

Wind power that is one of the new and renewable

energy has been considered as a subject in many re-

searches because it repr esents cle an energ y and low power

generation costs. Although the wind power has been de-

veloped based on large-scaled power generation systems

around the world, researches on small-scaled wind power

generation systems have been largely performed in recent

years. However, such small-scaled power generation sys-

tems show difficulties in starting a system and generatin g

power under the conditions of varying wind directions

and velocities at a low altitude because it applies a mi-

niature version of the large-scaled system.

In this study a simple wind tunnel is installed to de-

velop a small-scaled wind turbine generator as a vertical

axis drag type that shows efficient power generation un-

der the conditions of varying wind directions and veloci-

ties through introducing a simple wind tunnel. Then, the

mechanical and electrical power generated by a windmill

in a given wind speed are empirically measured to ana-

lyze the relationship between the mechanical and elec-

trical power.

2. Definition of Power

First, Wind flow can generate mechanical energy by ro-

tating a windmill with blades and the mechanical energy

can produce electrical energy through a generator. The

wind power generated by wind is presented as Equation

(1) where Pw is power (W), p is air density (kg/m3), A is

a projected area (m3), and V is wind speed (m/s).

Pw = pAV3/2 (1)

The mechanical power is defined by a mechanical pa-

rameter, Torque (T), and angular speed (w) as Equation

(2). Figure 1(a) shows an experimental configuration for

measuring its mechanical property.

Pm = T∙w (2)

The electrical power is defined by electrical parame-

ters, Voltage (V) and Current (I), as Equation (3). Figure

1(b) shows an experimental configuration for measuring

its electrical property [5 ].

Pe = V∙I (3)

3. Wind Tunnel Conditions

The output of the blower in the configured wind tunnel

presented in Figures 2 and 3 can be controlled with six

different steps and the wind speed can also be varied by

changing the steps. Table 1 shows th e averag e wind speed

in which the measurement is performed with a distance

of 3.5 m from the blower to the wind turbine generator.

4. Small-Scaled Wind Generator

The small-scaled wind turbine generator as a vertical axis

An Experiment on Power Properties in a Small-Scaled Wind Turbine Generator

7

(a) Mechanical power

(b) Electrical power

Figure 1. Block diagram for power evaluation process.

Figure 2. Wind tunnel.

Figure 3. Anemometry.

Table 1. Average wind speed at blower step.

1 setp 2 setp 3 setp 4 setp 5 setp 6 setp

dniWdeepS (s/m) 3.68 4.49 5.75 6.8 7.6 7.96

drag type consists of four different sections such as wind-

mill, gearbox, generator, and controller. The overall con-

figuration is presented in Figure 4. As the windmill is

Figure 4. Hybrid.

rotated by wind flow, the rotational energy, which is mul-

tiplied by four times through the gearbox connected to

the windmill, is transmitted to the generator. The gene-

rator produces currents and voltages using a 24 V con-

troller and the currents are stored in a battery.

An Experiment on Power Properties in a Small-Scaled Wind Turbine Generator

8

4.1. Windmill and Gearbox

The windmill presented in Figure 5 includes an oscilla-

tion unit, which optimizes the direction of blades accord-

ing to drag blades and wind conditions, and an axis of

rotation. Also, a gearbox that multiplies the low rotation

of the vertical axis windmill as shown in Figu re 6. Table

2 shows the specification of the parts employed in the

windmill [1-4,6].

4.2. Generator

As shown in Figure 7, a coreless generator by AFPM

(Axial flux Permanent Magnet), which has been known

that it can minimize cogging torque because it does not

use an iron core in its coil, is appropriate to small-scaled

wind turbine generators that represent difficulties in start-

up. Table 3 shows the specification of the generator.

(a) Wind millb (b) Blade

(c) Oscillating unit

Figure 5. Parts of windmill.

Figure 6. Gearbox.

Table 2. Specification of windmill.

Diameter of windmill Φ1460

Number of Blades 12

Height of windmill 1200 mm

Width of blade 350 mm

Oscillating angle ±35

Gearbox ratio 1:4

Figure 7. Generator.

Table 3. Parameter of generator.

AC-Voltage 24 V

Voltage Output AC (3Phase)

Rotor Permanent magnet type

Startor Coreless

Constant Output 200 W

Speed Rated 150 rpm

Speed Constant 191 V/rpm

Resistance (Line-Line) 0.728 Ω

4.3. Controller

As the controller is a hybrid type of wind and solar pow-

er and controls 50 0 W wind and power respectively. The

controller uses a maximum power point tracking (MPPT)

method as an off-grid contro l typ e. Also , i t perfor ms charg-

ing/discharging according to batteries. In addition, it in-

cludes a system protection function that protects the con-

troller and battery by separating the windmill from the

controller as a no-load state through cutting currents in

considering voltage increases caused by strong wind flow

like a typhoon and prevents the system from over-charg-

ing, over-discharging, over-current, and over-voltage. Fig-

ure 8 shows the controller and its circuit.

5. Experiments

5.1. Experiment on Mechanical Power

Figure 9 represents the experimental set-up for measur-

ing the mechanical power. The mechanical power can be

measured by pressing the mechanical energy generated

by wind speed to a powder brake and torque and RPM

sensors are used to measure the power.

An Experiment on Power Properties in a Small-Scaled Wind Turbine Generator

9

(a) Controller

(b) Circuit diagram

Figure 8. Controller.

5.2. Experiment on Electrical Power

The ex perimental set-up for measuring the electrical pow-

er is presented in Figure 10. The mechanical energy gen-

erated by wind energy is transmitted to the generator and

the generator measures voltages and currents using the

controller.

6. Results

6.1. Maximum Mechanical Power Line

Figure 11 shows the torque and RPM graphs presented

by measuring the mechanical power. Using these graphs,

the mechanical power curve based on the measured tor-

que and RPM can be defined as shown in Figure 12.

Also, in measuring the power varying steps, 1 - 6, the

mechanical power curve can be presented in Figure 13.

In addition, the maximum mechanical power line of the

windmill can be determined by connecting each maxi-

mum point.

6.2. Generated Electrical P ower Line

Figure 14 shows the electrical power line measured

through the experiment of the electrical power. The

power produced by the generator according to varies in

(a) Windmill (b) Fixture

(c) Power supply (d) Torque sensor

(e) Power brake

Figure 9. Mechanical power measuring system.

(a) Windmill (b) Fixture

(c) Generator (d) Controller

(e) Battery

Figure 10. Electrical power measuring devices.

An Experiment on Power Properties in a Small-Scaled Wind Turbine Generator

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Figure 11. Torque & RPM.

Figure 12. RPM vs. Power & Torque curves.

An Experiment on Power Properties in a Small-Scaled Wind Turbine Generator

11

Figure 13. Maximum power line on mechanical power curve.

Figure 14. Electrical power curve.

An Experiment on Power Properties in a Small-Scaled Wind Turbine Generator

12

the wind speed of the blower is stored to a battery and

the average of the data obtained by its monitoring is also

presented.

7. Conclusions

In this study the output of a small-scaled wind turbine

generator as a vertical axis drag type is investigated in a

simple wind tunnel and the relationship between the elec-

trical and mechanical data is also considered. The small-

scaled wind turbine generator is configured with a blade

width of 350 mm, a height of 1.2 m, a diameter of ϕ1460,

an oscillation angle of ±35, and a gear ratio of 1:4. Then,

the mechanical and electrical power are measured in the

simple wind tunnel. Regarding experimental methods, the

torque and RPM are measured in the mechanical experi-

ment by applying loads to a powder brake with a con-

stant wind speed for different six blower steps. In the

case of the electrical experiment, voltages and currents

are measured at the same wind speed as the mechanical

experiment. The results are determined by power lines as

represented in Figure 15 and the relationship between

the mechanical and electrical power in this small wind

turbine generator is also verified. A commercial coreless

generator, AFPM, is used to measure the power and that

is used to det erm ine t he m aximum power ge nerat i on point.

Table 4 represents the measured power of the wind

turbine generator in which Power 1 of the mechanical

power corresponds to the maximum value. The efficien-

cy for the maximum mechanical power is Eff. 1. In addi-

tion, the mechanical power adopted in the condition

above 24 V is presented in Power 2 where the efficiency

is presented in Eff. 2. In this experiment, it is verified

that the high efficiency more than 75% is determined at

the wind speed more than 5 m/s (Step 3). Thus, it is ex-

pected that the data analyzed using the empirically ob-

tained mechanical and electrical power will contribute to

obtaining the specification of a wind turbine generator,

which produces the maximum power.

Figure 15. Curves of mechanical and electrical powers.

Table 4. Power data of small-scaled wind generator.

Electrical Mechanical Efficiency (%)

Rpm Power (W) RPM Power 1 (W) Power 2 (W) Eff.1 Eff.2

1 step 142.8 4.68 84.51 17.67 7.77 26.47 60.21

2 step 151.8 19.76 107.4 35.21 28.14 56.14 70.23

3 step 162.15 50.6 132.96 66.87 62.86 75.67 80.49

4 step 172.35 86.02 157.79 113.22 111.99 75.98 76.81

5 step 183.9 124.26 178.85 156.81 156.65 79.24 79.32

6 step 186.45 131.82 187.25 172.32 172.31 76.5 76.5

An Experiment on Power Properties in a Small-Scaled Wind Turbine Generator

13

8. Acknowledgements

This research is financially supported by Changwon Na-

tinal University by in 2013-2014.

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