Grid Interconnection of Wind Turbines

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Grid Interconnection of Wind Turbines

• Presentation to GERC
• Ahmedabad
• 07.02.09
• M.P.RAMESH, former Executive Director
• Centre for Wind Energy Technology

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GERC posers

• GERC has put up the following questions
• Intra-state grids
• Interstate regional grid
• Bulk quantity of wind/solar inputs in low load
  areas impact assessment
• Increasing wind/solar inputs - need for backing
  down ?
• Limits?

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GERC Posers

• What are problems associated with wind power
  commercial implications?
• Technologies for scheduling/dispatch
• On-line monitoring
• Solar power generation
• Relevance of intra-state grid connectivity for
  major wind solar energy inputs
• Some insight into the wind potential in GUJRAT

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Some history

• Gujarat is THE FIRST STATE which experimented
  with grid connected wind turbines.
• The state also was the first state to have
  commercial wind farm at Mandvi.
• The states wind map shows second highest
  potential nearly everywhere adding up to 10645 MW
  (installed) based on certain assumptions.
• CWET/MNRE would be getting the atlas prepared for
  India shortly. We would then have a more
  comprehensive idea about the possibilities.

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Installable Wind Power potential in India (2006
estimate)
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Wind farming areas
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Gujarat wind Potential

• It is seen that a large part of Gujarat has
  moderate wind potential.
• But for a few pockets, the wind turbines would
  have good steady winds during monsoon months.
• A well defined May to August SW high wind season
  a moderate NE wind season during
  December-January.
• Year on year variations are well with in
  reasonable limits
• Wind power quite evenly distributed across the
  State.

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Some time scales in grid management

• There are four levels in grid management.
• Unit commitment which works on a scale of days
• Scheduling needed on a day upon day basis
• Load following which has a time scale of minutes
  to hours
• Regulation which happen over seconds to minutes
• We need to understand that it is a complex issue
  and needs detailed analysis either to accept or
  reject an idea.

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Evacuation The big picture Northern
Southern Grids
NR
NER
ER
WR
Freq - 1
SR

• 5 Regional Networks in the Country
• Currently 4 Regional Networks merged

Freq - 2
INDIA CURRENTLY OPERATING AT TWO FREQUENCIES
NORTH SOUTH
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INTER-REGIONAL EXISTING CAPACITIES
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INTER-REGIONAL PROPOSED CAPACITIES BY 2011-12
4600 MW
13450 MW
ER
6450 MW
1000 MW
EASTERN REGION
1300 MW
3700 MW
Weak link
30,000 MW OF INTER-REGIONAL POWER BY 2011 -12
NO Augmentation proposed between Southern
Northern Grids
SOURCE CEA
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Impact on grid and associated equipment

• As such, wind turbines and associated equipments
  are designed to take care of each and every
  eventualities that the installations would be
  subjected over their service life.
• Double redundant safety systems including
  electrical equipments are a type certification
  requirement.
• In India it is not possible to grid connect wind
  turbines which do not have a valid type
  certificate.
• Therefore a wind farm would work much like a
  standard power plant in all respects.
• The problems of first generation wind turbines
  have been very largely addressed in the modern
  wind turbines.
• MODERN WIND TURBINES MEET THE MOST STRINGENT GRID
  REQUIREMENTS FOR SAFE OPERATION.

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Impact on grid and associated equipment

• After the area and capacity of a given wind farm
  are decided, Wind farm design preceded by
  detailed load flow analysis, impacts of voltage
  frequency excursions, harmonics, seamless power
  factor controls and optimised.
• There are wind turbines which have facility to
  provide leading pfs if required.
• Wind farm Substations are built to meet strict
  standards laid down by the TRANSCos.

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Backing down Thermal ?

• The question of backing down of thermal power
  stations due to presence of large wind is open
  ended. It is a combination of many factors.
• In a surplus power supply system there could be a
  need to back-down some flexible generation
  facility (Hydro/gas based system for example).
• In our context, when grid frequency is lt 50 hz,
  there will be some margins that takes care of the
  so-called infirm power.
• Therefore in all likely hood there may be no need
  to back down thermal stations.
• If we integrate different regions effectively,
  flexibility would improve so that resources could
  be utilized far more efficiently.

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Is there any limit?

• In Denmark presently about 21 of energy
  consumed is supplied by wind turbines alone.
• Penetrations of wind power into local grids have
  at times gone upto 60 in good windy season.
• In Tamilnadu we have over 4000 MW against 12000
  MW of the so called firm power. That is about
  33 on installed power basis. If we consider a
  50 plf in high wind season, we are looking at a
  penetration level of18 on an average.
• As such there is no limit. It essentially
  depends on resources and grid management
  strategies.

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Infirm power?

• EB Comments from a state that has topped the Wind
  Power deployment for decades has this to say
• .. while occasionally the wind slows down in
  one location leading to decreased output in a
  particular location (also within the particular
  pass itself, the wind mills are installed over a
  radius of 30 to 40 KM), locations with high
  penetration of wind energy would compensate for
  the same. As a result, it typically takes much
  time or even hours for the total wind energy
  output of a region to change significantly. This
  makes it relatively easy for the utility system
  operators to accommodate these changes without
  relying on the reserves i.e. slowly taking the
  tag of infirm power out of wind energy.

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Effect of aggregation

• Just to illustrate the observations of the EB
  engineers some sample wind farms in Karnataka
  were chosen.
• A total capacity of about 300 MW from three areas
  within a radius of 50 km were considered.
• Real time data from these wind farms have been
  collected and the outputs summed up to on a 24
  hour basis during high wind month and a moderate
  wind month.

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(No Transcript)
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Though there is much variation, the ramp-up
ramp down happens over several hours
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Some observations

• With more and more wind farms coming on stream
  from different geographical locations, the
  averaging effect will be even more pronounced.
• The changes in delivered power are not drastic
  and sudden.
• It provides time to the system manager to take
  corrective measures

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Technologies available for scheduling/dispatching

• A system manager has to continuously monitor both
  the supplies and loads.
• While supplies could be controlled to some
  extent, loads can only be anticipated and
  corrective measures taken.
• In this dynamic situation it is important to note
  that it is a balancing act with or without
  wind/solar power on the grid.
• With wind having its variability, the management
  would have to be only slightly more innovative.
• There are emerging technologies to forecast in
  short term (horizon of 60 hours).
• Validation and implementation is some distance
  away.

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Some forecast results
It may be seen that the general trends are
predicted with some degree of uncertainty. There
are issues of input data for such exercises such
as outputs of Global Circulation Models.
Accuracies of input data for GCMs etc. are again
sources of errors. It is a well known fact that
the model outputs will come with uncertainties
and validation takes some time, funds and effort.
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On-line monitoring

• Online monitoring of wind turbines is a reality
  of the day. It is not uncommon in new wind farms.
  They are specifically designed SCADA systems used
  to centrally monitor and control wind farms in a
  given area.
• It is possible to obtain near online info from
  wind farms in a limited way.
• Though theoretically it is possible to have GSM
  connectivity, V-SAT terminals etc.., bandwidth
  related issues still exist.

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Intra-grid

• Studies have shown that it is most desirable to
  have these connectivity's in place.
• In the context of RE technologies, it would add
  some more flexibility to the local grid
  management to have conduits to bigger networks.
• Inter-regional exchange of power has larger and
  generally positive ramifications.
• It is much like the golden quadrilateral which
  has virtually revolutionized connectivity to
  rural India.
• Thank You for your attention.