Grid Integration of Large Scale Wind Turbines
Equipped with Full Converters: Belgian Case Study
Simon De Rijcke,
1
KULeuven
simon.derijcke
@esat.kuleuven.be
Hakan Ergun,
KULeuven
hakan.ergun
@esat.kuleuven.be
Abstract
This paper describes the results of a study
regarding the integration of wind power into the
Belgian electricity system. The main focus of
this study is the contribution of wind power
plants to reduce voltage deviations due to load
and wind power variations. It is shown, how
wind power plants can maintain and improve
the voltage in the existing electricity network
using
their
reactive
power
operation
characteristics. To cover a broad variety of
study cases, two different locations with
different characteristics are analyzed. One
location is situated near strong grid points,
whereas the second location is situated in a
more remote area. Additionally a series of
scenarios are applied to these locations to take
into account varying wind power generation
and variation of the loads for 2020. Study
results show that the added value of wind
power plant support is strongly related to the
connection point for the wind farms. Although
wind power plants may contribute to voltage
control in every area, they prove to be much
more useful for remote areas in which voltage
and reactive power problems occur much
easier than in the neighborhood of strong
connections, especially when a large amount
of wind power is integrated into the power
system. On top of conventional voltage control
on radial feeders, the studied wind power
plants are capable to control the voltage in the
whole area.
Keywords:
Wind
turbines,
voltage
deviations, reactive power, Direct-Drives.
1 Introduction
Since wind turbines reached the highest
number of installed capacity over one year for
several years, it is not surprising that this is
one of the fastest growing energy generating
technologies these days. The first generation
principle widely implemented over the world,
the Squirrel Cage Induction Generator (SCIG)
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1
Katholieke Universiteit Leuven, Kasteelpark Arenberg 10
Bus 2445, 3001 Heverlee, Belgium
Kristof De Vos,
KULeuven
kristof.devos
@esat.kuleuven.be
Johan Driesen,
KULeuven
johan.driesen
@esat.kuleuven.be
with fixed speed, is being overtaken in
numbers by the Doubly-Fed Induction
Generator (DFIG) and recently the Direct-Drive
Synchronous Generators (DDSG) [1]. These
units have a higher energy output over the
year due to the variable speed and pitch
control, but they also offer much more
possibilities regarding system support or
ancillary services. Moreover, wind turbines
have evolved from small distributed generation
units, to large units of several megawatts.
These units exceed the size of distributed
generators and consequently, they are more
frequently coupled to the transmission grid,
requiring more from generators, compared with
distribution grid requirements, as described in
grid codes [2].
One of the largest wind turbines being built are
DDSG units of 7 MW. Eleven of these wind
turbines are being connected to the grid in
Estinnes, Belgium in the framework of the
European 7-MW-WEC-by-11 project [3]. As it
is the first wind farm with turbines of that power
class in the world, this prototype project is
meant as a first evaluation to assess the
introduction of large scale wind turbines in a
commercially exploited wind farm, onto the
market. With the upcoming high capacity wind
farms, onshore and especially offshore, a
better understanding of their behavior is
essential. Moreover, the possibilities to support
the power system are essential with the rising
penetration rate of these wind turbines.
This study analyses the impact of these large
scale wind turbines, equipped with DDSGs, on
the power system and to which extent they can
support the grid.
Therefore, two main case studies are
envisaged. The first encloses the current
situation of the Belgian grid at which the
turbines are connected. Therefore, a reduced
grid model of the Belgian grid surrounding the
wind turbines installed at Estinnes is modeled.
The 7 MW DDSG model is constructed by
Enercon [4]. Combining both models, a
realistic case study is obtained.
A second case study focuses on the
performance of large scale integration of wind
power. Therefore, a reduced grid model of a
more remote area in the Belgian power system
is modeled where a relatively large share of
wind power is integrated. By this case study,
the performance of these wind turbines is
assessed as they may help to solve severe
voltage deviations in weak network regions.
Although it is not the only cause, the lack of
reactive power plays an important role, when it
comes to voltage instability issues [5].
Therefore tap changing transformers and static
reactive power compensation devices are used
for thirty years by transmission system
operators [6]. On the other hand, wind turbines
equipped with DDSG have a flexible and broad
active/reactive power operation range in
comparison with FSIG and DFIG, which could
substitute reactive power compensation
devices. Figure 1 shows the flexible
active/reactive power characteristic of wind
power converters equipped with such turbines
[7].
scenarios simulated. Thereafter, sections 3
and 4 discuss the simulations of the scenarios.
2 Scenarios and grid models
This section discusses the set of parameters,
which the scenarios are based upon. The
following parameters are explained in detail in
the following subsections: grid topology, time
horizon, wind penetration and load level. The
last subsection summarizes all parameters in a
set of scenarios, which are used for further
analysis.
2.1
Grid
The study is focused on the Belgian grid.
Consequently, the grid snapshots investigated
are representative for the Belgium. The study
starts with the analysis of a real case study,
which is the integration of eleven wind turbines
in Estinnes. This area is defined as very strong
due to the highly meshed grid and a high short
circuit power. Therefore, the impact of wind
turbines is rather limited as will be explained by
the simulation results.
To emphasize the impact of wind turbines
equipped with full converters, a second grid
case study is defined in which the impact is
more severe. Both grid cases are explained in
detail in the next two subsections.
2.1.1 Grid Estinnes
Figure 1 Active and reactive power capability of a
selected wind turbine with two different reactive power
options
The benefit of this PQ operation range is due
to the electric decoupling of the generator from
the grid by using power electronics [7]. The
extensive reactive power capability may
improve reactive power management on the
long term and due to the fast acting IGBTs,
these wind turbines can be very useful in
supporting the power system during grid
transients.
This study shows how these wind turbines,
with their flexible character, can maintain and
even improve the stability and operational
safety of transmission grids. The focus of this
study is to reduce voltage deviations due to
load and wind power variations and reactive
power balancing in a specified region. The first
section discusses the grid topologies and
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1
Katholieke Universiteit Leuven, Kasteelpark Arenberg 10
Bus 2445, 3001 Heverlee, Belgium
As explained above, the grid surrounding
Estinnes is highly meshed. Figure 2 illustrates
the composition of the grid, which is modeled.
All wind turbines are connected to the power
system by a step-up transformer at a voltage
level of 70 kV. From this bus bar, connections
to both the 70 kV and the 150 kV grid exist. By
exploring the surrounding grid, it becomes
clear that two main loops are visible, both with
a different voltage level. The loops are
interconnected
by
two
tap-changing
transformers and one fixed transformer.
Further grid connections are represented by
Thévénin equivalents. Two capacitor banks are
located at the outer ends of the 150 kV loop.
2.1.2 Grid remote area
The grid area in the south of Belgium consists
of a 70 kV zone which is connected to the high
voltage grid by two tap changing transformers
and several fixed ratio transformers. The zone
contains two switchable capacitor banks.
Figure 3 illustrates the topology.
[MW]
2010
2020
Estinnes
85
119
Remote
120
630
Table 1 Installed capacity of wind turbines
Figure 2 Grid topology around Estinnes
Re.
Est.
[MW]
Low wind
Low
High wind
Prod.
Load
Prod.
Load
11
220
134
220
1
High
20
380
142
380
Low
157.5
126
630
126
High
157.5
380
630
380
Base case
Prod.
Load
41
307
120
253
Table 2 Scenario details
2.4
Figure 3 Grid topology in remote area
Major differences occur when comparing both
grids. Before simulating, it is worth analysing
these differences. First, the grid topology in
Estinnes is highly meshed with short lines, has
many connection points to the 150 kV grid and
much generation in the neighbourhood (not
indicated on the figures). In the remote area of
Belgium, the grid is mostly at 70 kV, has
relatively long lines and few generation units.
Secondly, wind penetration changes from low
at Estinnes to high in the South, which will be
confirmed by numbers in subsection 2.3.
2.2
Time horizon
Load level
Again, for both time horizons 2010 and 2020,
load levels for the whole of Belgium are
determined. The load for Estinnes is assumed
to be a mix of residential and industrial loads.
Therefore, this load is expected to follow the
total load in Belgium. The numbers for 2010
are based on load data available from the
Belgian TSO [8] and predictions for 2020 are
based on predictions by Elia. In the low load
case, the load is in 99% of the cases higher
than the chosen level. For the high low case,
this is the opposite.
For the remote area the approach is slightly
different. This area is assumed to have mainly
residential and to a very small extent industrial
loads. The correlation between the total load
and the individual load profiles is thus
expected to be very high. First the peak load is
determined. Thereafter, the low, medium and
high load scenarios are calculated by
multiplying the peak load respectively with
0.25, 0.50 and 0.75.
The simulations are performed both for 2010
and 2020. However, because wind penetration
is rather low at 2010 and to keep the results
surveyable, only results of 2020 are discussed
in this work.
Although this the difference in approach
between Estinnes and the remote area may
change the result details, the general
conclusions remain. This is due to the strong
grid connections in Estinnes and the relatively
higher impact of wind then load variations.
2.3
2.5
Wind integration
Installed wind capacity is determined for both
time horizons (2010 and 2020) and both
locations. Table 1 summarizes all details. For
Estinnes, the newly installed wind farm of 77
MW is yet included in the numbers.
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1
Katholieke Universiteit Leuven, Kasteelpark Arenberg 10
Bus 2445, 3001 Heverlee, Belgium
Scenarios in numbers
All performed simulations are summarized in
Table 2. This data set is for 2020. A few
remarks clarify the numbers in this table. For
1
The generation level changes between low and high load
for Estinnes because of modeling reasons: The
conventional production is raised and lowered according to
the load level. This is not done for the remote area. This
difference does not influence the simulation results.
1,03
1,02
Voltage magnitude [p.u.]
each location (Estinnes and remote area), a
high and low load level are simulated in
combination with high wind and low wind. The
load levels coincide with the levels presented
in section 2.4. These scenarios can be
compared with a base case for both locations.
For each scenario, production and load are
given. Production covers all kinds of
production, including wind. The power factor is
generally 0.9, except for wind, power factor
equal to 1 is assumed. Load has a power
factor of around 0.95.
Base Case
High wind - high load
1,01
1
0,99
0,98
0,97
0,96
0,95
1 2 3 4 5 6 7 8 9 101112 131415 161718 192021 2223242526
Bus number (bus 1-12: 150 kV, 12-26: 70 kV)
Figure 4 Voltage magnitudes for base case and case
with high load and wind2
Simulations in sections 3 and 4 are performed
with these numbers.
1,02
3.1
Simulations without reactive
power support of wind turbines
Votlage magnitude [p.u.]
3 Simulations – Estinnes
1,01
Base Case
Low wind - high load
1
0,99
0,98
0,97
Altogether, differences are small and
restricted. Variations in voltage magnitude are
between 0.975 p.u. and 1.02 p.u. This is due to
several reasons. First, the highly meshed grid
and short lines avoid voltage drop on the lines.
Secondly, wind penetration is low in
comparison with the many generators around
Estinnes, which are modeled by Thévénin
equivalents. Thirdly, the strong connection
between 70kV and 150kV by tap changing
transformers allow to control the voltage on the
70kV level. Consequently, voltage variations
due to seasonal load variations are easily
controlled.
0,95
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26
Bus number (bus 1-12: 150 kV, 12-26: 70 kV)
Figure 5 Voltage magnitudes for base case and case
with low wind - high load
1,03
1,02
Voltage magnitude [p.u.]
Figure 4 to Figure 7 illustrate the voltage
magnitude at all modeled buses around
Estinnes for each scenario defined above.
Although the combination of load and
generation generally determines the final
impact on voltage, it is concluded that the
small penetration of wind power does not affect
the voltage magnitude severely. It is rather the
load level, with a relatively higher power
contribution, that gives rise to most voltage
differences.
0,96
Base Case
High wind - low load
1,01
1
0,99
0,98
0,97
0,96
0,95
1 2 3 4 5 6 7 8 9 1011121314151617181920212223242526
Bus number (bus 1-12: 150 kV, 12-26: 70 kV)
Figure 6 Voltage magnitudes for base case and case
with high wind - low load
1,02
Voltage magnitude [p.u.]
This section describes the simulations results
for the scenarios described above in the grid
area surrounding Estinnes. The planned
capacity of wind turbines is relatively low and
will impact voltage magnitudes to a rather
small extent. To evaluate the impact of the
high capacity wind farm installed in Estinnes
on grid voltage, all four scenarios summarized
in Table 2 are compared with the base case.
1,01
Base Case
Low wind - low load
1
0,99
0,98
0,97
0,96
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26
Bus number (bus 1-12: 150 kV, 12-26: 70 kV)
Figure 7 Voltage magnitudes for base case and case
with low wind - low load
2
The bars are always positioned in the same way the
labels are to avoid confusion. Primarily from left to right
and secondarily from up to bottom.
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1
Katholieke Universiteit Leuven, Kasteelpark Arenberg 10
Bus 2445, 3001 Heverlee, Belgium
3.2
Simulations
with
reactive
power support of wind turbines
(a)
From the former section, one may conclude
that there is no immediate need for reactive
power support from the wind turbines installed
at Estinnes. However, it is investigated how
these wind turbines may contribute to voltage
control by analyzing two cases in the
subsequent sections.
3.2.1 Voltage boost in a remote
area
The reactive power boost has as consequence
a high voltage at the point of injection, which is
due to the grid topology and cannot be
avoided, unless the tap changing mechanism
is enabled. But, with a reactive power injection
from the wind turbines, the voltage of the 70 kV
can easily be controlled in this area, without
the need for tap changing transformers.
Without going into juridical and economical
issues, this exercise shows that the reactive
power capability of wind turbines is able to
replace the function of tap changing
transformers to boost the voltage. By analyzing
the voltages on Figure 9 , one may conclude
that the voltage is lifted in the whole 70 kV
area. This idea may give rise to a shift from
traditional voltage control on distribution
feeders [9] by wind turbines to voltage control
by wind power plants in areas. The idea of
voltage control by distributed units, instead of
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Katholieke Universiteit Leuven, Kasteelpark Arenberg 10
Bus 2445, 3001 Heverlee, Belgium
(b)
(c)
Figure 8 Voltage profile from remote bus to bus at
Estinnes (a) base case, (b) with tap changers, (c) with
reactive power boost by wind turbines.
1,05
Base Case
1,04
Voltage magnitude [p.u.]
This section studies how the wind power plant
at Estinnes can control the voltage at a remote
bus. From all voltage Figures, the lowest
voltage occurs in bus 26. It represents the
radial feeder at the left bottom in Figure 2. The
voltage at this point can be raised by injecting
reactive power or by changing the taps of the
70-150kV transformers. Both methods are
illustrated in Figure 11. The upper figure (a),
illustrates the base case, in which the tap
changers control the voltage at their low
voltage bus bars. In the second figure (b), the
left transformer on Figure 2 is used to set the
voltage at the remote bus to 1 p.u. This
conventional method works properly, if the
second tap changing transformer connected to
150 kV is fixed in order to prevent
counteraction and consequently overloading of
the tap changing transformer. The third figure
(c), shows the voltage profile in case of a
reactive power boost of 20 MVar of the wind
turbines and with the tap changing
transformers fixed to their original state. Using
this method, the voltage at the remote bus is
also raised to 1 p.u.
With Reactive Power Injection
1,03
1,02
1,01
1
0,99
0,98
0,97
0,96
0,95
0,94
1
2
3
4
5
6
7
8
9 10
Bus number (70 kV level)
11
12
13
14
Figure 9: Voltage magnitudes before and after reactive
power injection by wind turbines at Estinnes
keeping the power factor constant, has been
investigated earlier and has been proven more
effective in view of higher distributed energy
penetration [10].
3.2.2 Substitution
banks
of
capacitor
In this subsection, the capacitor bank on the
right of Figure 2 is lowered in capacity from 75
MVar to 40 MVar. Therefore, 35 MVar of
reactive power is injected by the wind turbines
to compensate the missing reactive power.
The power flows before (base case) and after
the reactive power boost are given in Table 3.
The symbols are clarified by Figure 10.
Most of the reactive power is evacuated to the
150 kV grid by the tap changing transformer
and the fixed transformer. The taps of the left
Figure 10 Power flow symbols at the PCC of Estinnes
[MW/MVar]
To 70
To Tap
Q boost
47.2/18.5
0.5/24.7
Base case
45.6/8.9
-0.5/10.9
1.6/9.6
1.0/13.8
To 150
Slack
Q boost
-42.5/-14.3
0.34/0.55
Base case
-39.6/-23.7
0/0
-2.9/9.4
0.34/0.55
Table 3 Power flows before and after a reactive power
boost of 77MVar by the turbines at Estinnes.3
and right transformer change respectively from
12 to 13 and 13 to 15 to keep the voltages in
between boundaries. The reactive power also
partly flows into the 70 kV system. Again,
without considering juridical and economical
issues, wind turbines may replace other
sources of reactive power for steady state
purposes in the near area. Moreover, reactive
power injection can be set at any preferable
set point, compared to the capacitor banks with
discrete taps. Active power flows stay almost
unaffected.
4 Simulations – Remote Area
4.1
Figure 11 Voltage profiles on two selected feeders for
the base case 2020
Simulations without reactive
power contribution of wind
turbines
In this section the simulation results for a
remote area in southern Belgium is shown. In
this area the wind farms are connected to the
transmission grid on the 70 kV level. The
planned capacity of wind power for 2020 will
exceed the expected peak load in this area.
3
The total difference does not equal 35 Mvar because of
losses mainly due to the step-up transformers between the
wind turbines and the grid.
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Katholieke Universiteit Leuven, Kasteelpark Arenberg 10
Bus 2445, 3001 Heverlee, Belgium
Due to changing wind and load conditions
situations with high power flows on the 70 kV
lines can occur, if the generation and the
demand do not match. In such cases reactive
power within the zone is required to
compensate reactive losses on the lines. On
the other hand transport of reactive power
causes voltage deviations, which can be high
depending on the required reactive power [6].
Figure 11 shows the voltage profile on a
selected feeder in the base case of 2020.
Because both feeders illustrated have the
lowest occurring voltage in the whole area, it
can be observed that in this operation scenario
no under voltage violations occur. In further
analysis with a high degree of wind integration
and increasing load (Figure 16), this picture will
change and problem situations will appear.
In this operation scenario it can be seen that
the voltages on these feeders are in a range
between 0.99 and 1.002 per unit. Additionally
shows Figure 12 that the voltages for the base
case are in a range between 0.99 and 1.03
p.u.
In case of high wind power generation and low
demand, the voltages in the whole area
increase. This is not surprising because in this
operation point the power injected by the wind
turbines is four times higher than the demand.
This problem is already emphasized in
literature and is one of the most prominent
problems of integrating distributed energy
sources in remote areas [11]. The voltages in
the base case and the high wind – low load
case are compared in Figure 12.
1,1
1,03
Base case
1,08
Base case
1,02
Low load - high wind
High load - low wind
Voltagemagnitude in pu
Voltagemagnitude in pu
1,06
1,04
1,02
1
0,98
1,01
1
0,99
0,98
0,96
0,97
0,94
0,92
0,96
A1 A2 B1 B2 C1 C2 D F H1 H2 H3 M1 M2 M3 N1 N1 O R1 R2 S1 S2 T W
A1 A2 B1 B2 C1 C2 D F H1 H2 H3 M1 M2 M3 N1 N1 O R1 R2 S1 S2 T W
Bus Name
Bus Name
Figure 12 Voltages at all buses in the base case and
the high wind - low load case
1,05
Figure 14 Voltages of all buses for the base case and
low wind - high load case
1,05
Base case
1,04
Low load - low wind
1
Voltagemagnitude in pu
1,03
Voltagemagnitude in pu
Base case
High load - high wind
1,02
1,01
1
0,99
0,98
0,95
0,9
0,85
0,97
0,96
0,8
A1 A2 B1 B2 C1 C2 D F H1 H2 H3 M1 M2 M3 N1 N1 O R1 R2 S1 S2 T W
A1 A2 B1 B2 C1 C2 D F H1 H2 H3 M1 M2 M3 N1 N1 O R1 R2 S1 S2 T W
Bus Name
Bus Name
Figure 13 Voltages on all buses in the base case and
the low wind - low load case
Figure 15 Voltages of all buses in the base case and
the high wind - high load case
The voltages on the most buses increase in
this scenario. At some buses the voltage does
not change. The reason for that is that these
buses, which are the borders to neighboring
areas, are simulated as PV nodes with reactive
4
power limits . This means the bus is modeled
as a PV node until a certain reactive power
limit is reached and it is modeled as a PQ node
when the reactive power limit is reached. In
this case it can be seen that on some nodes
the reactive power limits are reached and a
lack of reactive power occurs, what causes
decreasing voltages on these busses.
reactive power limits of the PV nodes are not
reached. Due to the fact that less active power
is exported out of the area, compared to the
high wind - low load case, which causes less
reactive losses on the lines, less reactive
power is required.
Figure 13 shows the voltages of the operation
scenario low wind – low load. In this case the
wind generation is approximately the same as
the demand in that region. Due to the fact that
there are also other production units, the
production is higher than the demand in that
region. The voltages in this case are not as
high as in the high wind – low load case
(Figure 12). It can also be observed that all
voltages are equal to or higher than the base
case voltages. This means that in this case the
4
The reason for this kind of modeling is that the maximum
reactive power, which can be transmitted by the
connection points to the neighbouring regions, is unknown.
Therefore the maximum transferable reactive power is set
to the value of the largest capacitor bank within the region.
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Bus 2445, 3001 Heverlee, Belgium
In the low wind - high load case, the load in the
region is approximately three times the
generated wind power. In this operation
scenario the voltages decrease on buses with
limited reactive power injection (PQ nodes)
due to the high loads connected on these
buses.
Figure 14 shows the voltages for this case.
The worst operation scenario concerning grid
voltages is the case high wind – high load. In
this case the voltages can decrease to values
below 0.9 per unit. Figure 15 and Figure 16
show respectively the voltages on all buses
compared to the base case and the voltages of
two selected feeders (comparison to Figure
11).
1,05
High load - high wind
High load - high wind, voltage control without comp.
Base case
Voltagemagnitude in pu
1
0,95
0,9
0,85
0,8
A1 A2 B1 B2 C1 C2 D F H1 H2 H3 M1 M2 M3 N1 N1 O R1 R2 S1 S2 T W
Bus Name
In this scenario the buses, which are
connected to neighboring areas, reach the limit
of exchangeable reactive power and a lack of
reactive power occurs in the analyzed area,
although two capacitor banks and two tap
changing transformers to 380 kV network are
existent in this area. In this subsection the wind
turbines are operated with a constant power
factor. The next subsection shows simulation
results, where the wind turbines contribute to
voltage control.
4.2
Simulations
with
power contribution
turbines
reactive
of wind
The broad reactive power range of the wind
turbines as shown in Figure 1 is used to
restore the voltages in challenging operation
cases. Depending on their size, wind farms
can be able to replace capacitor banks, which
are connected close to the wind farm. If for the
wind turbines voltage control is used, then for a
low wind – high load situation the voltages can
take the same values occurring at the base
case as shown in Figure 17. In a high wind –
high load case the voltages can be kept in a
range between 0.97 and 1 p.u.
1,05
High load - high wind
High load - high wind, voltage control
High load - low wind, voltage control
Base case
Figure 17 also shows that in the voltages in the
high load – high wind case can be restored by
using the wind turbines even if both capacitor
banks are disabled (green bars).
Figure 18 shows the voltages in the base case,
the voltages with capacitor banks and without
voltage control of the wind turbines
respectively the voltages without capacitor
banks and with voltage control of the wind
turbines. For the low wind - high load case,
the voltages can always be kept above 0.95
p.u., if the capacitor banks are disabled and
the turbines are voltage controlled. Figure 19
illustrates the voltages for the base case, the
low wind - high load case with capacitor banks
and without voltage control respectively without
compensation and with voltage control.
1,05
High load - high wind
High load - low wind, voltage control without comp.
Base case
1
0,95
0,9
0,85
0,8
A1 A2 B1 B2 C1 C2 D F H1 H2 H3 M1 M2 M3 N1 N1 O R1 R2 S1 S2 T W
Bus Name
1
Voltagemagnitude in pu
Figure 18 Voltages with and without capacitor banks
resp. without and with voltage control of wind turbines
for high wind – high load
Voltagemagnitude in pu
Figure 16 Voltage profile on two selected feeders with
high wind and high load
Figure 19 Voltages with and without compensation
resp. without and with voltage control of wind turbines
for low wind - high load
0,95
0,9
0,85
5 Conclusions
0,8
A1 A2 B1 B2 C1 C2 D F H1 H2 H3 M1 M2 M3 N1 N1 O R1 R2 S1 S2 T W
Bus Name
Figure 17 Voltages with and without voltage control of
wind turbines
______________________________________________
1
Katholieke Universiteit Leuven, Kasteelpark Arenberg 10
Bus 2445, 3001 Heverlee, Belgium
This paper investigates the impact of wind
turbines
equipped
with
direct-drive
synchronous generators, with extensive and
flexible reactive power capabilities, on the
Belgian grid. Therefore, two case studies with
a time horizon of 2020 are simulated:
integration of a wind power plant in an area
characterized by a meshed grid which is typical
for Belgium, and large scale integration of
these wind turbines in a remote area in
Belgium. From the simulations, the integration
of a wind power plant at Estinnes does not
cause any difficulties for the grid. There is no
immediate need for reactive power capabilities
from the wind turbines; however this does not
exclude support to the grid.
With large scale integration of wind power
plants in a remote area, requirements for
reactive power from the wind turbines are
necessary. Especially in case of high wind
power, being four times the load in the studied
area, voltages rise to unacceptable values,
wherefore reactive power compensation from
the wind turbines is required. Because a wind
power plant can control the voltage at the
terminals, all wind power plants can easily
control the voltage in the whole remote area
from inside, contrary to traditional voltage
control by tap-changing transformers on
selected nodes.
To conclude with, this study proves that wind
power plants equipped with direct-drive
synchronous generators can support grid
control in both a meshed and remote area. On
top of the conventional control at remote/radial
feeders, wind power plants are able to control
the voltage in a whole area. In remote areas,
this support is required to safeguard correct
operation and avoid the installation of
additional grid supporting elements.
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______________________________________________
1
Katholieke Universiteit Leuven, Kasteelpark Arenberg 10
Bus 2445, 3001 Heverlee, Belgium
Energieversorgung 1. Berlin - Heidelberg,
Germany: Springer Verlag, 2007.
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