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= Tampereen yliopisto
Tampere University

Exam

EE.REE.320 Wind Power Systems

One sub-question per question is asked in the exam.
The sub-question is selected randomly.
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- Tampereen yliopisto 2 (6)
Tampere University

Question 1: Wind turbines

1. Explain and analyse the reasons for the growth of wind power in Finland and
globally.

2. Describe the wind farm. What components are included and what are the
roles and purposes of those components. Remember to give a good
overview, but also explain the most important details. Provide also a short
comparison of onshore and offshore wind farms from electricity grid
perspective.

3. Describe the methods how wind turbines are extracting and maximizing the
power from wind. Consider also the differences between different wind
turbine schemes.

4. Describe the three main wind turbine schemes (fixed-speed, double-fed
induction generator and full rated converter) on overall level. Compare the
schemes also from component and performance viewpoints.
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- Tampereen yliopisto 3 (6)
Tampere University

Question 2: Generators

1. Describe the general structure of model of one wind turbine scheme. Explain
also the purpose of each component in the general model. You may select
the wind turbine scheme (fixed-speed, double-fed induction generator and
full-rated converter) based on your own favor.

2. Describe the electrical characteristics of fixed-speed induction generation
wind turbine scheme. Give the answer based on information related to grid
connected induction generator. Consider both the steady-state and dynamic
characteristics of fixed-speed wind turbine. Name also which of these
characteristics are the most important from grid integration perspective.

3. Describe the electrical characteristics of full rated converter wind turbine
scheme. Give the answer based on information related to grid connected
induction generator. Consider both the steady-state and dynamic
characteristics of fixed-speed wind turbine. Name also which of these
characteristics are the most important from grid integration perspective.

4. Explain the role of power electronic converters/technologies in wind turbine
schemes. Explain also what power electronic technologies are typically
utilized in wind farms.
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- Tampereen yliopisto 4 (6)
Tampere University

Question 3: Steady-state grid impacts

1. Describe and explain the most important and influential grid code
requirements for the wind turbines. Explain why those requirements are
important from grid perspective. In similar way explain why those are
influential from wind turbine perspective.

2. Large wind farm needs to participate in grid voltage control. At the same time
the wind farm should maintain as good reactive power balance as possible.
Describe and explain different possibilities how the wind farm may realize
the voltage control and reactive power management, describe, and explain
also the challenges related to those in case of a wind farm.

3. Explain what kind of power flow variations will happen due to large-scale
wind power connected to high voltage and extra high voltage distribution
and transmission grids. Explain local, regional and system level impacts and
provide explanation for the differences between them.

4. Large-scale expansion of wind power will require the extension of grid
capacity as well. Consider what challenges and solutions grid companies
have to answer this task cost effectively from the whole electricity system
viewpoint in the long run. Consider all levels of grid expansion: wind farm
connection, regional grid, national transmission grid and import/export
capacity to neighbouring countries and market areas.

5. Describe what is the overplanting of a wind farm and how it may be realized.
Explain also why it may be beneficial for the owner of the wind farm.
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- Tampereen yliopisto 5 (6)
Tampere University

Question 4: Dynamic grid impacts

1. Large-scale wind power may endanger power system security if not properly
taken into consideration. Explain first what the power system is and how the
large-scale wind power may endanger it. Explain also in detail how those
mechanisms/solutions help power system and what impacts they have for
wind turbine design and operation.

2. Describe what is the fault-ride-through capability and how it is related to
power system security. Explain also how a wind turbine may fulfil this
requirement.

3. Wind farm may participate in frequency control. Describe different methods
how wind farm may participate in frequency control from technical
perspective and how those methods may be implemented in wind farms.

4. Wind farm may provide ancillary services for distribution and transmission
grids. Describe and explain what ancillary services wind farms may provide
and how they may realize those. Consider both the technical and market
aspects of ancillary service provision.

5. How the frequency stability of low-inertia power system may be enhanced?
Explain alternative solutions and what kind of role they may have in future
100 % renewable based power system.
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- Tampereen yliopisto 6 (6)
Tampere University

Question 5: Market impacts

1. Forecasting of wind power has important role in the market operating of
producer. Explain shortly the main idea of large-scale wind power
forecasting. What consequences forecasting error has for the producer?
What factors influence wind power forecasting error? How the error might
be reduced?

2. Explain why and how the smoothing of wind power variation is realized.
Explain also what kind of benefits smoothing has for power system
operation.

3. What kind of impacts large-scale wind power has for the prices of day-ahead
and regulation power markets. Provide explanations.

4. Explain why the volatility of electricity market price (e.g., day-ahead market
system price) will increase due to large-scale wind power production.

5. Describe what kind of impacts large-scale wind power has for control and
disturbance reserves. Explain why these happen.