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Tampere University of Technology
Electrical Engineering

Wind Power Systems DEE-54107 20.12. 2017

Enrigue Acha Programmable calculator allowed 5 guestions/ & 6 p

Ouestion 1:
A) State three different types of information contained in a wind rose. (1p)

B) Sketch a typical characteristic of power coefficient versus wind speed for a
practical wind turbine, labelling all its relevant points, e.g., cut-in wind speed. (1p)

C) Draw the output power-wind speed characteristic of a wind turbine and label all its
relevant parts. (1p)

D) Sketch a family of characteristics of the power output (P7) of a wind turbine versus
rotational speed of the shaft turbine (&), for three wind speeds (say V3>V2>V1 ).

(Ip)

E) Describe how the power take-up may be controlled in a fixed-speed 1.5 MW wind
turbine. (1p)

F) Describe briefly the role of the gearbox in a commercial 5 MW variable speed

wind turbine using a Fully Rated Converter, Permanent Magnet Synchronous
Generator (FRC-PMSG). (1p)

Ouestion 2:
A) Discuss briefly the advantages and disadvantages of offshore wind farms
compared to onshore wind farms. (2p)

B) Explain the term array loss in connection with a wind farm. (1p)

c

-

Consider the layout of an offshore wind farm with 16 turbines with the disposition
shown in Figure 1. Each turbine is rated at Pe = 6 MW. The rotor diameter D of
each turbine is 126 m. The turbine hub height is 135 m. The wake decay coefficient x is

0.037251.
5D HET)
N O--0--0--0--0
7D| 5D 5D SD
veli 6 0=0 00 =
n i [7
0--0--0--0--0
wind
direction
Figure 1

1(2)
Tampere University of Technology
Electrical Engineering

Enrigue Acha

Ouestion 3:

Ouestion 4:

Ouestion 5:

A)

B)

0)

A

z

B)

Wind Power Systems DEE-54107 20.12. 2017

Programmable calculator allowed 5 guestions/ä 6 p

The wind speed Viat the ith turbine in the row may be determined using the
following empirical eguation (notice that the front row is row zero):

V,=v, :l - li -f)1-c, )-(O/(D +2x -dD))')

Assume that the wind speed reaching the first row of turbines is 10 m/s, the torgue
coefficient Cr is 8/9 and d=7D is the vertical distance between adjacent rows of
turbines. The power output of the turbine is represented by the following analytical
expression between the cut in and cut out wind speeds:

P, =3743xV? —0.077977 x P,
The cut-in wind speed is 5 m/s and the rated speed is 12 m/s. Determine: (a) the
wind speed that reaches each turbine in the wind farm for the case when the
prevailing wind is from the South, as indicated by the thick arrows in Figure 1;
(b) the total power output of the wind farm. (3p)

State the main differences, in terms of connection to the AC system, between a
doubly fed induction generator (DFIG) and a FRC PM synchronous generator
when used in a wind turbine application. What advantages does the former
generator have over the latter? (2p)

State briefly the main construction differences that exist between a three-phase PM
synchronous generator and a conventiona! three-phase synchronous generator. (2p)
x 4
Kap
Sketch the power-angle characteristic of a PM synchronous generator of the type
used in wind power applications. (2p)

Sketch the per-phase eguivalent circuits of a three-phase, doubly fed induction
generator and a three-phase PM synchronous generator, labelling carefully all the
resistance and reactance components in both eguivalent circuits. (2p)

Derive expressions for the active powers and the reactive powers at the generators”
terminals, as a function of their eguivalent impedances as seen from their
respective terminals and their terminal voltages. (4p)

Describe in detail the role that power electronics-based technologies may play in
providing reactive power support and in evacuating the electrical power output of large
wind parks. Use as many eguations and diagrams that you may find appropriate to aid
your description. (6p)

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