reducing contingency-based windfarm curtailments through ...€¦ · wind pattern, maximizing...
TRANSCRIPT
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Reducing Contingency-based Windfarm Curtailments
through use of Transmission Capacity Forecasting
Minnesota Power Systems ConferenceSt Paul, MN
November 6-7, 2018
Doug BowmanSouthwest Power Pool
Jack McCallLindsey Manufacturing Co.
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Background
• Within SPP is the 159.1 MW “Grand” windfarm• Output travels through 2 outlet transmission paths
G
PCCBus H
Bus N
Bus S
GRAND Windfarm
G GWindfarm N
Windfarm S
Bus L
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The Need for Curtailment• Wind Integration Study showed with normal
conditions and N-1 limits, one or the other line would become overloaded.
• To address these situations, up to 48.7 MW (~30%) of Grand’s power production must be curtailed.
G
PCCBus H
Bus N
Bus S
GRAND Windfarm
G GWindfarm N
Windfarm S
Bus LPreemptive 30% CurtailmentOrder
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Initial Solution• In the first three months after the curtailments
were ordered, over 50,000MWh were curtailed.• Loss of over $1 million in revenue• Loss of over $1 million in production tax credits
• Grand’s owner: this “hurts us, our off-taker and the market efficiency”
• Remedial Action Scheme (RAS) requested be put in place to reduce curtailments
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Proposed Fast Reaction RAS Scheme• Monitor the three N-1 lines (PCC-H, PCC-N, N-S)• For any trip, immediately curtail 49.7MW of capacity• SPP ensured the scheme would have minimal
likelihood of mis-operation and had no unintended consequences.
G
PCCBus H
Bus N
Bus S
GRAND Windfarm
G GWindfarm N
Windfarm S
Bus L
RAS
30%Curtailment
Order
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Approach Summary• The Preemptive Order and the Reactive
RAS did the same thing…• Used curtailment to address N-1
conditions caused by:• Fixed capacity line capacity ratings, during
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Approach Summary• The Preemptive Order and the Reactive
RAS did the same thing…• Used curtailment to address N-1
conditions caused by:• Fixed capacity line capacity ratings, during• Periods of high wind farm output,
resulting from
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Approach Summary• The Preemptive Order and the Reactive
RAS did the same thing…• Used curtailment to address N-1
conditions caused by:• Fixed capacity line capacity ratings, during• Periods of high wind farm output,
resulting from• Windy conditions
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Approach Summary• The Preemptive Order and the Reactive
RAS did the same thing…• Used curtailment to address N-1
conditions caused by:• Fixed capacity line capacity ratings, during• Periods of high wind farm output,
resulting from• Windy conditions
Is there another way?
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What limits line rating?
Clearance to Ground• A line is not safe unless clearance is
maintained• Compliance requirementsConductor Temperature• Overheating leads to weakening
and loss of life • Premature replacement
What effects these parameters? Weather.
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Optimizing line capacity based on weather
• Line ratings (static) are based on conservative weather conditions
• Seasonal Adjusted Ratings and Ambient Adjusted Ratingsrecognize weather related effects on line capacity
• Both adjust only on ambient temperature
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• Line ratings (static) are based on conservative weather conditions
• Seasonal Adjusted Ratings and Ambient Adjusted Ratingsrecognize weather related effects on line capacity
• Both adjust only on ambient temperature
• Wind has MUCH more impact than ambient
• +2 mph wind ≅ 15°F change
Optimizing line capacity based on weather
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BUT, DLR•Changes rapidly•Changes erratically•Is Real-time
Dynamic Line Rating
Decades of studies show +10-25% capacity availability 95% of the time
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BUT, DLR•Changes rapidly•Changes erratically•Is Real-time
Dynamic Line Rating
Decades of studies show +10-25% capacity availability 95% of the time
What is my next DLR rating?
Use of real-time DLR is operationally difficult.
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BUT, DLR•Changes rapidly•Changes erratically•Is Real-time
Dynamic Line Rating
Decades of studies show +10-25% capacity availability 95% of the time
?
?
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Like a map app in a traffic jam…
Dynamic Line Rating
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Like a map app in a traffic jam…
Highly accurate but useless.…Real-time is too slow
Dynamic Line Rating
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Generation is FORECAST because it varies
Load is FORECAST because is varies
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Generation is FORECAST because it varies
Load is FORECAST because is varies
Yet transmission capacity is generally assumed as fixed
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Transmission Capacity Forecasting
What is it?•An advanced statistical process that provides:• Forecasts of transmission line
capacity from 1-hour to 1-week ahead
• Very high (98% or greater) confidence factors
• Local line measurements avoids weather-only errors
•Can provide direct EMS input•Combines:
• Learning-based conductor behavior models
• Continuous Forecasting
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Transmission Capacity ForecastingSMARTLINE-TCF
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Is It Windy Enough for TCF to Work?
• The worse case line needs 147.4% of Static to avoid any curtailment.
• All lines are perpendicular to prevailing wind pattern, maximizing cooling effect
• Lowest Monthly Ave Wind is 3.3m/sec• Ave Annual Wind Speed is 6.8 m/sec• 3.0 m/sec (6.7mph) ground wind speed
delivers 150% of line static rating• Analysis shows 9.6 m/sec ground wind
speed is needed to produce max wind farm output
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TCF with Pre-Emptive Curtailment A. Develop 36-hour ahead forecast
of line capacities• Provides for 24-hour day ahead
operation• Additional 12 hours for market setting
and clearing activities
B. Take day ahead forecasted wind farm output to forecast flows on lines of concern during N-1
C. If A<B, then order pre-emptive curtailment
D. Alternatively, order a lower level curtailment to match A and B
A<B?
Wind Farm Forecast
A
B
Develop N-1 Line Flows
Develop 36-Hr Line Forecast
Order Curtailment
YES
Trim Curtailment
for A=B
NO
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Supervising RAS Curtailment with TCFRecall the RAS was to curtail within cycles of line tripA. Develop 4-hour ahead forecast of line capacitiesB. Take day ahead forecasted wind farm output to forecast
flows on lines of concern during N-1• If A>B, then INHIBIT curtailment IF an N-1 event occurs• Refresh signals periodically to continue to inhibit or allow
curtailment to be issued.
Supervision of RAS by TCF Forecast
A>B?
Refresh signal every 60 minutes
D
Activate RAS
A
B
Compute N-1 Overload MVA
4-Hour TCF forecast MVA
True if N-1 active
YES
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Enhancing RAS Curtailment with TCF Recall the RAS was to curtail within cycles of line trip.C. Develop 6-hour ahead forecast of line capacities• Check if A is close to the forecast flows on lines of concern
during N-1• If A≅B, then pre-emptively reduce wind farm output so that
A>B to avoid initiating the instantaneous RAS curtailment in the event of a N-1 event
A>B?
Refresh signal every 60 minutes
D
Activate RAS
A>C?
A
B
Reduce Wind Farm Output
6-Hour TCF forecast MVA
Compute N-1 Overload MVA
YES
4-Hour TCF forecast MVA
True if N-1 active
YESC
Supervision and Tapering of RAS by TCF Forecast
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Who Pays | Who BenefitsWho Pays
Financial Benefit Operational Benefit Notes
TO • If NITS, None• If not, transmission revenue
Enhancement to asset capabilities
Possible addition to rate base
RTO None; Not able to pay • Great situational awareness
• More flexibility in power export
• Less congestion
Must socialize cost if RTO orders the installation
WF • Energy sales• PTC
Less wear and tear on equipment due to curtailment
Must negotiate with TO to install and operate to forecasted levels
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Summary• TCF systems can effectively address transmission
constraints that result in wind farm curtailment• Can supplant and/or enhance traditional curtailment
methods
• Allocating costs of deploying and integrating TCF systems is not well defined
• TCF systems, once installed, provide additional operation benefits to wind farm operators, TOs and RTOs
• Changes fixed transmission assets to dynamic