Considerations in wind power plant 110 kV grid

Considerations in wind power plant
110 kV grid connection planning
Petri Koski
Adviser, Empower Oy, Power network division
19.3.2014
Contents
• Specifying and selecting the grid
connection point
• Design and building
• Testing and commissioning
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The power system of a wind power
plant
• Each wind turbine has its own low voltage power
system
• The electrical power is transformed to medium
voltage and transmitted to the connection point
through a medium voltage grid
• Often the power is transformed to high voltage
between the medium voltage grid and the
connection point (often referred to as ”PCC”,
point of common coupling)
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Example of a power system of a
wind power plant
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WPP medium voltage grid basics
• The medium voltage (MV; 1 kV < Un < 70 kV) power
system components between and including the turbine
step-up transformers and the PCC form the medium
voltage grid of the WPP
• The WPP medium voltage grid’s purpose is to transmit
the generated electricity to the PCC with low losses
• Underground cables are almost exclusively used
• Turbine switchgear can be installed inside the WTG
towers or outside them
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WPP medium voltage grid, cont’d
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High voltage power system components
in a wind power plant grid
•
If the wind power plant grid contains any high voltage (HV)
components, they are usually
• The MV/HV power transformer(s)
• A HV transformer bay
or a whole HV switchyard
• A HV power line
•
In very large wind power
plants, there might be
several HV substations
and HV power lines
between them
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So you want to build a wind power
plant…
• … and generate electricity. Where do you
connect your power plant to the grid?
• The power grid of today is extensive –
quite likely there are power lines or even a
substation nearby
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110 kV power lines
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A 20 kV power line
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A large substation (220 kV)
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A small substation (110/20 kV)
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A tiny secondary substation (20/10
kV)
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Determine your technical needs for
the grid connection
• The connection point must be carefully
selected
• How much power could be injected to the
PCC?
• Evaluation of the need for reliability of the
PCC
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Examples of how to improve PCC
and substation reliability
• Multiple feeders connected to the grid
• Advanced switchyard layouts
•
•
•
•
Double busbar or double breaker
Transfer bus + bus coupler
Bus sectionalizer
Three-winding power transformers
• Redundant auxiliary power supply
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Rough estimations for the required
connection point
Rated power of wind
power plant (MW)
Demand for the
reliability of the PCC
An example of a PCC
0…3 MW
Very low
Direct connection to an
existing 20 kV line
3…10 MW
Low
20 kV substation
10…25 MW
Low
110 kV power line or
substation
25…100 MW
Medium
110 kV or 220 kV substation
100…200 MW
High
110…400 kV substation
200+ MW
Very high
400 kV substation
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Start the talks with the local grid
operator(s)
• Find out who owns and operates the
grid(s) near your wind power plant (WPP)
site
• Present your case and the technical facts
• The grid owner will present a rough idea
about the PCC, the ownership limits and
an estimation about the connection fee(s)
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Estimate the grid connection costs
• When consensus about the grid
connection has been reached with the grid
owner, calculate the expenses and
proceed with preliminary design of the
substation and the wind power plant MV
grid
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Prerequisites of MV grid design
• The ideal workflow for
MV grid design is
shown in the diagram
• These project phases
are often intertwined
→ the steps might
have to be iterated
Wind turbine locations, land lease agreements
Wind turbine generator (WTG) type selection
Wind measurements and production estimations
Road planning
MV cable route pre-planning
MV grid loss calculation (load flow studies) and voltage
level selection
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Cable routes and topology
• For small or medium-sized wind power
plants and problematic terrains, the MV
cables may be planned to be installed
along the roads
• For larger wind power plants, consider
algorithm-based grid topology optimization
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From MV grid design to substation
design
• When the MV grid topology is confirmed, the
following has been selected:
•
•
•
•
Cable routes
Cable types and cross-sections
Number of feeder bays required at the substation
Number of RMU bays required at the wind turbines
→This is essential input for substation preplanning and MV grid detail planning
• Consider also maintenance and spare parts
when selecting the power system components
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Discuss the grid connection with the
grid owner and WTG manufacturer
• Issues to discuss:
PCC and the grid
code (version) to
be applied
MV grid and
substation
topology
Earthing method of
the grid
Short-circuit
studies and preplans for relay
protection
SCADA communications
overview and possible
information interchange
between operators
Simulations and
simulations models
to be provided to
the grid owner
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Advanced grid studies
• Dynamic performance simulations of the
WPP and its controllers
• Stability simulations
• Harmonic current analysis
• Hazard voltage studies
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Compensation equipment
• Reactive power, earth fault current or
harmonic currents might have to be
compensated
• Evaluate the need for compensation in
close co-operation with the WTG
manufacturer
• Compensating equipment might be costly
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Avoid unnecessary expenses and delays
by clearing the technical questions early
• It’s essential to talk about the details of
grid connection issues with the grid owner
and the WTG manufacturer early enough!
• Supply times for WTG components,
substation components, software
modifications etc. may be very long
• Additions might require extra switchgear
cubicles / bays
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Power transformer selection
• The power transformer(s)
for the substation should
be ordered early due to
long supply times
• Special considerations in
wind power projects:
• Weighting of price, load
losses and no-load losses
• Two or three windings
• Type of windings in case of
unusual MV grid earthing
methods
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About undersizing power system
components
• Undersizing power system components might be
attractive in wind power projects
• If you wish to undersize,
• Get the grid owner’s approval
• Be careful with the studies / simulations
• Get the available overloadability information from equipment
manufacturers
• Ensure that electrical safety rules are fulfilled
• Implementing automatic production limiter logic
requires time and effort. Estimate carefully if it’s
worth it or not.
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About wind power plant MV power
system protection
• Usually the relay protection of a wind
power plant MV grid is easy to implement
• Possible considerations:
• Infeed of short-circuit current from WTG’s → Directional
protection needed?
• Protection-related information interchange between substations /
WTG’s
• Protection and control related information interchange between
substation automation systems and/or WPP SCADA
• Coordination of protection settings with grid code requirements
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Commissioning
•
•
The substation is commissioned first. After that, special care must
be taken in MV system installations
When the WTG commissioning starts, the operational status
usually changes several times. This is an electrical safety hazard.
Never underestimate the probability of human error!
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Grid connection tests
• The grid owners usually require grid connection
tests for the wind power plant
• The tests must be planned early enough
• Don’t select the date right after commissioning…
• … or too late
• The responsible persons from at least the WTG
manufacturer and grid owner(s) must attend the
test
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Grid connection tests, continued
• Grid connection test content is specified in
the grid code and/or grid connection
agreement
• Any tests of special power system
components, logics etc. shall be agreed
upon separately
• The tests shall be sufficiently recorded
(voltage, powers, frequency etc.)
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Grid connection tests, continued
•
Sufficient wind speed is required for full, successful tests
•
A good practice is to reserve several weeks in the attendees’
calendars. In case of low wind, the tests are postponed to the next
already reserved week
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Summary
• Wind power plant power system planning has some
extra features compared to regular medium/high voltage
power system planning
• Form a good overall vision about the grid connection
together with the turbine manufacturer and the grid
owner as early as possible
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Summary, continued
• The workflow might not
be ideal, it depends on
the project – having many
”moving pieces” easily
results in iteration and
delays
• Special power system
components and grid
studies might be required
Wind turbine locations, land lease agreements
Wind turbine generator (WTG) type selection
Wind measurements and production estimations
Road planning
MV cable route pre-planning
MV grid loss calculation (load flow studies) and voltage
level selection
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Question time!
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