Transcript introduction

How Wind Farms
Affect The Grid Performance
Eng. Fatma Nada
Studies Consultant – EETC
1
March 2012
• Large wind farms are typically located
where good wind resources exist, and
are often far away from the main load
centres and strong AC network
connections.
• Large wind farms can result in major
changes to the load flow within the
network, causing real and reactive
power flows that were not experienced
before.
• Wind power stations have some features that
make their operational behaviour different
from that of conventional power stations,
which since many years have been the main
source of electrical energy.
• In line with such a spectacular increase of
wind power, there are several questions,
regarding the Integration of large scale wind
power into AC power systems that must be
clarified.
• This presentation will focus on the important
issues related to system operation, stability,
and protection when large scale wind power
plants are integrated into power systems.
1. The requirements for wind power plants for
transmission networks will be described.
2. Challenges and grid code’s technical
requirements in worldwide courtiers having
considerable share of wind power.
• These cover fault ride through, voltage and frequency
operating range, reactive power range/voltage
control, wind power forecasts requirements, as well as
remote operation requirements.
• From that point, the need to have different control
and protection philosophy in big electrical networks is
emphasized through using Real-Time Wide Area
Monitoring, Protection and Control systems (RT
WAMPAC).
• Within the ongoing rise in electricity demand, wind
energy will play a major role in the race to satisfy the
demand.
The world wide trend is to utilize the renewable
energy resources since the expected life time for
fossil fuel is about 30 -> 50 years
The target of
European countries
to reach
20 % by the year
2020
The typical wind farm output from Zafarana
during March 2010.
The GWH during year 2010-2011,this change
raise challenges for the integration of large amount
of wind power into the grid.
GWh output of the Wind Farm during 2010/2011
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20
0
Jan.
Feb
March
April
May
June
July
Aug.
Sep.
Oct.
Nov.
Dec.
 Large wind farms can result in major changes
to the load flow within the network, causing real
and reactive power flows that were not
experienced before.
 In line with such a large increase of wind
power, there are several questions, regarding
the Integration of large scale wind power into AC
power systems that must be clarified.
 How should wind farms be expected to behave
and perform?
which requirements should be imposed in order to
expect wind farms to support the system?
 Is it realistic to expect wind turbines and wind
farms to behave as any other conventional power
plant?
 What is the behaviour during grid faults/Fault ride thr
 What about reactive power compensation and
voltage control, voltage and frequency operating
range, remote data transfer andforecast issues?
In order to accommodated and safely operate a high level
of variable and uncontrollable wind power generation on a
power system, many challenge on both wind power
transmission technologies and transmission grid a raises,
this include:
1. Wind power forecasts requirements.
2.Fault ride through (FRT) requirements;
3.System frequency and frequency response requirements;
4.Transmission system voltage and reactive power
5.capability requirements;
6.Remote operation requirements;
Wind power forecast requirements
A forecast of wind generation is an additional input
to the pre-dispatch demand forecasting processes.
Grid Codes specify that controllable wind farms
should provide their wind power output forecasts at
least once a day for the following 48 hours for, as
an example, each 30-minute interval. A forecast
update must also be available in National Control
Center (NCC). The accuracy of the wind power
forecasts depends of a number of factors, the most
important being the wind speed forecast.
Large Scale Wind Generation
Energy Forecast
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1. REQUIREMENTS FOR WIND POWER PLANTS IN
TRANSMISSION NETWORKS
There are several issues should be taken into
consideration in grid integration of wind
turbines, guaranteeing a stable, profitable and
highly qualitative supply of wind energy :
1.Wind turbines have to be able to remain in
operation without reducing performance and
without time limits even with considerable
voltage and frequency fluctuations.
2. If voltage dips occur due to grid problems, wind
turbines have to remain connected to the grid for
a defined period of time.
3. Short-circuit current power feed-in may be
requested during a grid fault. Depending on the
grid, the turbine has to be able to feed in
primarily active or reactive power to the grid.
4. Abrupt grid frequency changes should not cause
the wind turbine to shut down.
5. During a failure and while a grid fault is being
cleared, reactive power absorption by wind
generators is restricted or not permissible at all.
6. After a fault has been remedied, a wind farm
should resume power feed as quickly as
possible within a specified maximum time range.
7. Wind farms should be able to operate with
reduced power output with no time restrictions.
8. For coordinated load distribution in the ride,
the increase in power output (power gradient),
for example when the wind farm is starting,
should be able to be restricted in accordance
with the grid operator's specifications.
9. Wind farms have to be able to contribute
reserve energy within the grid. If grid
frequency increases, the power output of a
wind farm should be reduced.
10. If necessary, wind farms should be able to
contribute to maintaining voltage stability in
the grid by supplying or absorbing reactive
power with no time restrictions. Dynamic
criteria to maintain grid stability must be met.
11. Wind farms must be able to be integrated
into the grid control system for remote
monitoring and control of all components in
the grid
2. CHALLENGES FOR GRID CONNECTION OF
LARGE WIND FARMS AND LESSONES LEARNED
•
1.
2.
3.
4.
5.
In order to accommodate and safely operate a
high level of variable and uncontrollable wind
power generation on power system, many
challenges
on both wind power transmission technologies
and
transmission
gird
operation
arise.
These include:
Fault ride through requirements;
System frequency and frequency response
requirements;
Transmission system voltage and reactive power
capability requirements;
Wind power forecasts requirements.
Remote operation requirements.
2.1 Fault (low voltage) ride through (FRT) requirements.
• The large increase in the installed wind capacity in
transmission systems necessitates that wind
generation remains in operation in the event of
network disturbances.
• For this reason, grid codes issued during the last
years invariably demand that wind farms (especially
those connected to HV grids) must withstand
voltage dips to a certain percentage of the nominal
voltage (down to 0% in some cases) and for a
specified duration.
• Such requirements are known as Fault Ride Through
(FRT) or Low Voltage Ride Through (LVRT) and they
are described by a voltage vs. time characteristic,
denoting the minimum required immunity of the
wind power station.
All LBRT requirements sited in the different grid
code. The requirement depend on specific
characteristics of each power system and the
protection employed , so they deviate significantly
from each other.
An example from Ireland represent the response of one
grid-connected double feed induction generator (DFIG)wind power station (WPS) during a 3-phase fault on an
adjacent 110 kV line resulting in a 30% voltage dip at the
CCP (note that the WPS still connected with the grid).
This particular WPS has separately installed capacitor
banks that support voltage at common coupling point
(CCP) and enhance WPS FRT capability. This WPS also
stayed connected for 70% voltage dip at CCP. For a high
wind penetration scenario, if the wind power plant is
removed from the generation pool during the slightest fault
event, it may induce the cascading effect commonly
associated with a pre-blackout event.
2.2 Voltage and frequency operating range
• Wind farms must be capable of operating
continuously within the voltage and
frequency variation limits encountered in
normal operation of the system.
• Further, they should remain in operation in
case of voltage and frequency excursions
outside the normal operation limits, for a
limited time and in some cases at reduced
output power capability.
The frequency responses of some of transmission
/distribution system operator (TSO/DSO) connected WPSs
during the tripping of one of the large units on the system.
All TSO connected WPSs stayed connected during the
frequency excursion; while some of the DSO connected
WPSs were tripped.
Recorded under-frequency responses
of some WPS
2.3 Reactive Power Range / Voltage Control
• A common requirement is that the wind farm
shall be able to operate with a power factor
anywhere between defined leading and
lagging power factors at the grid connection
point.
The decision of the working point that is generally
commanded by the grid operator.
Reactive power requirements in the UK grid code specified by National Grid
Point A is equivalent (in Mvar) to: 0.95 leading Power Factor at Rated MW output
Point B is equivalent (in Mvar) to: 0.95 lagging Power Factor at Rated MW output
Point C is equivalent (in Mvar) to: -5% of Rated MW output
Point D is equivalent (in Mvar) to: +5% of Rated MW output
Point C is equivalent (in Mvar) to: -12% of Rated MW output
2.4 Wind power forecasts requirements.
• A forecast of wind generation is an additional
input to the pre-dispatch demand forecasting
processes.
• Grid Codes specify that controllable wind
farms should provide their wind power
output forecasts at least once a day for the
following 48 hours for, as an example, each
30-minute interval. A forecast update must
also be available in National Control Center
(NCC).
2.5 Remote operation requirements.
•
These requirements include the feasibility to
exchange signals between WPS and TSO. Among the
signals that WPS should make available to the TSO’s
remote terminal units (RTU) are:
1. Grid connected transformer (GCT) tap positions;
2. Voltage at the GCT low voltage terminals;
3. Active and reactive power output at the LV side of
the GCT;
4. Voltage regulation system set-point (in kV);
5. On/Off status indications for reactive power
devices;
6. MV Circuit-breaker position indications.
Remote operation requirements.
3. THE NEED FOR WAMPAC
• SCADA-systems provide only a steady state slow
picture in much longer time intervals.
• However, Synchrophasor technology in power
systems has opened up new possibilities for
better real-time monitoring and control of system
wide area events.
• These measurements can be used as system
snapshots and therefore, show the dynamics of
the power system.
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• Synchrophasor is considered to be the main
core of Real Time Wide Area Monitoring,
Protection and Control (RT WAMPAC)
• The Synchrophasors system is designed to
operate in parallel with the existing
SCADA/EMS system and maximizes the mutual
benefits in power system RT WAM PAC.
• The new system of RT WAM PAC fills the
coordination and speed gaps between the very
fast dynamic local protection systems and the
slow static SCADA/EMS systems.
The new system of RT WAM PAC fills the coordination
and speed gaps between the very fast dynamic local
protection systems and the slow static SCADA/EMS
systems .
Example
• Remote wind generation is transmitting power over a
simplified cross-country two-terminal line.
• Each end is monitored by a phasor measurement ( PM)
unit and sending time-synchronized measurement data
to the master station in order to visualize the relative
phase angle and frequency variations between the
source and load
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CONCLUSIONS
• WP differs from the traditional power generation
sources because of its intermittent varying
nature. WP imposes many technical requirements
and challenges of different aspects.
• The fast growing penetration of the WP within
the existing grids has to be faced by adding new
equipments and technologies to adapt the grid
capabilities
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CONCLUSIONS (cont.)
• New Grid Code requirements are necessary. New
philosophy and tools for the protection and control
strategy of the grids utilizing phasor measurement
( PM )has to be developed and applied
• The relatively fast performance of the closed
control loops using synchrophasor data via fast and
robust communication permit facing the effect of
the intermittent and variable nature of the WPS.
This can be achieved by fast-acting equipment such
as SVC, HVDC, FACTS, PSS.
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