RENEWABLE ENERGY SOURCES LABORATORY Department of Chemical Apparatus and Theory of Machines Faculty of Chemistry, Gdańsk University of Technology

LABORATORY INSTRUCTION NO. 4-EW WIND TURBINE

WIND TURBINE

Purpose of exercise The purpose of the exercise is determining the work range & power generated with an WT, as well as drawing a WT power characteristic curve in a function of wind velocity: P = f (V w) and, based on the results, determining: o start-up point of the WT and the wind velocity, at which the turbine's generator starts charging the battery; o nominal velocity point - wind velocity, at which the WT reaches rated power; o shut-down point - wind velocity, at which the WT shuts down due to safety factors.

DETERMINING THE WORK RANGE AND POWER CURVE OF A WIND TURBINE IN A FUNCTION OF WIND VELOCITY

WT - Wind turbine (Fig. 1) (aero-generator) - a wind engine connected (most commonly through a gearbox) with a power generator. A wind engine is any flow device, utilizing the energy of an airflow to produce mechanical energy.

Fig. 1. Simplified scheme of a WT The components of a WT (Fig. 1) include, among others: rotor (comprising of: a hub (1) and blades (2)), nacelle (10) (which houses: bearing (3), shaft (4), gearbox (5), break (6), coupler (7), generator (8) and a control cabinet (9)). This mechanism is embedded on top of a tens-of-meters-high tower (11). The use of WT Wind turbines generating tens to hundreds of Watts are mainly utilized in powering: cottages, yachts, camping trailers, mountain retreats, light advertisements, info panels, house & garden lighting. A rational concept is to combine a wind turbine with photovoltaic cells, which has a positive influence on power supply continuity. Furthermore, such hybrid systems (WT + PV) allow for lower installation costs, because two independent energy sources are exploited (wind and sun). In case of a single wind turbine installation, higher power needs to be installed, so that the energy accumulated within the batteries may be utilized during windless days. WT coupled with a PV module also work because of the specificity of atmospheric conditions. During windless days, solar irradiation is usually high, while clouds and rain are commonly accompanied by high velocity winds.

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Description of the WT study station

Fig. 2. The experimental station and its components. 1- fan, 2 - wind channel with a flow straightener, 3- power sockets, 4- variable-frequency drive (VFD), 5studied wind turbine, 6- wind direction & velocity sensor, 7- wind velocity recorder, 8- accumulator, 9digital multimeter, 10- WT components connector, 11- digital multimeter, 12- load circuit Description of the station's elements  Wind turbine Characteristic curves (Fig. 3) and technical parameters of the WT (Table 1) are presented below.

Fig. 3. Characteristic curves of WT

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Table 1. WT technical data Rotor Number of blades 3 Diameter [m] 1.00 Material Carbon fiber Electrical system Type of generator DC-excited Magnet Neodymium Nominal power [W] 40 Voltage [V] 12 (24, 48 optional) Performance Start-up [m/s] 3 Nominal power [m/s] 12.5 Mass [kg] 6 The module connecting the components of WT, with a battery, is shown in Fig. 4..

Fig. 4. Switchboard module and the battery The course of exercise To obtain the characteristic P = f (Vw) of power generated by the WT, in a function of wind velocity, and to determine the WT's technical parameters, the measuring system must be connected to the experimental station according to Fig. 5.

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Fig. 5. Setup of measuring devices Students conducting the exercise are required to properly connect the measuring devices - voltmeter & ammeter, to the studied system, conduct a series of measurements and - based on the obtained results - develop the WT's characteristic. To help achieve a proper connection of measuring devices and the system, Fig. 6 presents two electrical schemes for a WT working with external equipment. 6

A

B

B

A BA

G

V

BA G

V

Fig. 6. Possible methods of connecting the measuring devices G - direct current generator, V - voltmeter, A - ammeter, B - fuse, BA - battery (accumulator) Attention: Multimeter ranges should be set for measuring direct current & voltage! The voltmeter's range should be chosen with respect to the voltage, generated by the WT - to correctly assess the range, refer to the WT's technical data sheet (Table 1). The ammeter's range however should be chosen based on the battery's charging current, which changes with the rotation speed - this is why, at the beginning, it is recommended to set the ammeter's range to maximum value. This current can be calculated from the WT's P = f (Vw) characteristic, After properly connecting all the components, use the VFD to power up the wind simulator. The variable-frequency drive enables smooth regulation of the wind simulator's engine rotation speed. Conduct the measurements on various VFD settings, starting at the lowest values (e.g. 5), up until the maximum - 50.

Fig. 7. Description of VFD During consecutive measurements, measure the wind velocity Vw by setting the wind sensor in a proper position.

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Fig. 8. Wind velocity measurement Every time, measure the wind velocity in 3 survey points, marked on the floor and presented in Fig. 9.

Fig. 9. Survey points next to the "wind" simulator Note the obtained results in Table 2. Table 2 Data sheet No. 1 2 3 4 5 . . . n

VFD setting

Read in point -1

Read in point -2

Read in point -3

V1 [ m/s ]

V2 [ m/s ]

V3 [ m/s ]

Average Wind velocity Vav [ m/s ]

5 10 15 20 25 . . . 50

where: Vav =

V1  V2  V3 [ m/s ] 3

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Next step involves replacing the anemometer with the WT and powering up the simulator with the VFD (Fig. 10).

Fig. 10. Setting the WT at the base of the simulator When the WT stabilizes, read and note the values indicated on the measuring devices.

Fig. 11. Layout of the measuring devices Insert the successive measurements into the table. Table 3. Measurement results No. VFD settings

Vav [m/s]

U [V]

I [A]

P [W] P = U ∙ I [W]

1 5 2 10 3 15 6 30 … … 9 45 10 0 Based on the obtained results, draw the characteristic of the WT's power, as a function of wind velocity (Fig. 12).

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Charakterystyka

P = f (Vw)

15

[W]

10

P 5

0

4

5

6

7

8

9

10

11

Vw [ m/s ]

Fig. 12. Example of a WT characteristic. Using the prepared characteristic, determine: o WT start point - minimal wind velocity, at which the rotor blades start to turn; o nominal speed point - wind velocity, at which the WT reaches its rated power; o shut down point - wind velocity, at which the WT turns itself off due to safety factors. Calculate the energy conversion efficiency with the following formulas: Power of a wind stream, flowing with a velocity V[m/s] through an area A [m 2], expressed in Watts, is calculated from:

A V 3  W  P =   2

where:

 kg   - air density, normal conditions  = 1.25  3  ; m   - coefficient of power, which, depending on the WT's construction, is within the range of  = 0,3 ÷ 0,45 ; (choose lower value for calculations)  - efficiency. To determine the cross-section area A [m2], measure the wind channel's inside diameter:

 

d2 2 A m . 4

Calculate the efficiency for 4 different wind velocities. Insert the results in Table 4. Table 4. Results of calculation  No. Vw [m/s] P [W] 1 6 2 8 3 10 4 11

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