Current GB SQSS Approach

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Current GB SQSS Approach

• Cornel Brozio
• Scottish Power EnergyNetworks

Workshop 3 Birmingham, 10 January 2008
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This Presentation

• Overview of current SQSS methodology
• Interpretation of Planned Transfer and Required
  Transfer
• Variations on SQSS approach
• Comparison and Conclusions

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Approach 1 - SQSS Methodology

• Current method with wind AT 0.72
• Section 1.1, Appendix 3
• Different exporting and importing area wind AT
  (0.72/0.05)
• Section 1.3.1
• Variable wind A-factors
• Section 1.3.2, Appendix 4

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Current SQSS Methodology
1(a) 1

• Transmission boundary capability at ACS peak
• Planned Transfer (Appendix C of SQSS)
• Interconnection Allowance (Appendix D of SQSS)
• Required Capacity PTIA

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Setting up Planned Transfer
1(a) 2

• Ranking Order technique
• Set Plant Margin ? 20
• Assumption is that market will deliver around
  20, but many closures are unknown
• Plant least likely to run is treated as
  non-contributory
• Straight Scaling technique
• Scale generation to meet demand
• Scaling proportional to availability at time of
  ACS peak

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Ranking Order Example
1(a) 3
For ACS demand of 60GW
Less likely to run
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Wind Equivalent in Ranking Order
1(a) 4
Average P available from equivalent thermal unit
Average P available from wind generation
Wind generation registered capacity
Average availability of a thermal unit (At ? 0.9)
Registered capacity of equivalent thermal unit
Wind generation winter load factor (LWind ? 0.36)
Re 0.4 RWind
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Straight Scaling
1(a) 5
Power output of generator i of type T
Registered capacity
PTi S ? AT ? RTi
Availability at ACS peak
Match generation and demand (Applies to entire
network)
With a plant margin of 20 and AT 1.0, S
0.833
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Availability Factors
1(a) 6

• SQSS does not prescribe AT values
• Thermal and hydro units
• AT 1.0
• Wind generation
• AT 0.72

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Planned Transfer Example
1(a) 7
?RTi 10000 MW D1 6000 MW G1 8333 MW
AREA 1
PT 2333 MW
AREA 2
? RTi 62000 MW D2 54000 MW G2 51667 MW
System in Planned Transfer condition Total ACS
peak demand 60GW
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Interconnection Allowance
1(a) 8

• Planned Transfer condition set up
• Select boundary, i.e. split system into two parts
  
• Find IA from the Circle Diagram
• Boundary capability
• PT IA for N-1
• PT ½IA for N-2 or N-D

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Circle Diagram
1(a) 9
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IA Application Example
1(a) 10
Circle diagram x-axis
?RTi 10000 MW D1 6000 MW G1 8333 MW
AREA 1
PT 2333 MW
AREA 2
? RTi 62000 MW D2 54000 MW G2 51667 MW
y-axis 2.1 IA 1260 MW
System in Planned Transfer condition
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What does the IA provide?

• Capacity for a generation shortage in one area to
  be met by importing from another area (most of
  the time)
• N-2 or N-D requirement (PT½IA) can be met for
  ?95 of actual generation and demand outcomes at
  ACS peak, assuming
• Enough generation in the exporting area
• No local constraints

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Actual Boundary Transfer
Frequency
Boundary Transfer
Expected boundary transfer at ACS peak
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Variations Considered for Wind

• Keep PTIA and PT½IA at same percentile of
  possible boundary transfers
• Probabilities of exceeding N-1 or N-2
  capabilities remain broadly constant
• Variations considered
• Approach 1(b) Different wind A-factors for
  importing and exporting areas
• Approach 1(c) Variable wind A-factors based on
  wind volumes in each area

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Different Export and Import Wind A-factors
1(b) 1

• PT½IA captures all but the highest ?5 of
  boundary transfers
• When imbalance in available power is highest
• Should include imbalance due to wind conditions
• At 60 in PT, support from wind generation in
  importing area is over-estimated

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Importing Wind A-factor
1(b) 2

• In exporting area 60 is approximately P90 of
  wind output
• Mirror exporting area by using P10 of wind
  generator power output
• About 4 of rated capacity
• AT 0.05 (around 0.05 ? 0.833 0.04 in PT)
• Approach 1(b)
• Different (but constant) A-factors
• Exporting area AT 0.72 for wind (?60 in PT)
• Importing area AT 0.05 for wind (?4 in PT)

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Approach 1(c) Variable Wind A-factors

• Aims to find A-factors as functions of relative
  wind generation volumes for any boundary
• Monte-Carlo simulation to find distribution of
  transfers and find P99 and P95
• Using SQSS approach for same boundary, adjust
  wind A-factors until
• PTIA (N-1) matches P99 and
• PT½IA (N-2) matches P95
• with minimum error.

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Exporting Area Wind A-Factor
1(c) 2
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Importing Area Wind A-Factor
1(c) 3
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Results for 2007/8
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Results for 2020/1
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Summary

• Approach 1(a) Single A-factor (0.72)
• Works well, but over-estimates wind contribution
  in importing area
• Approach 1(b) - Different A-factors (0.72/0.05)
• Extends existing approach
• System security remains broadly constant
• I.e. probability of exceeding N-1 or N-2
  capability remains approximately constant
• Approach 1(c) - Variable A-factors
• Difficult to find robust A-factor functions
  (scatter on graphs)
• Additional complexity
• Except high-wind export boundaries, very similar
  RT to constant 0.72/0.05

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Drawback - Different PT for each Boundary

• Both variations of SQSS approach mean that PT
  becomes boundary dependent
• Different A-factors in each area
• Single PT condition no longer exists
• Importing and exporting areas not always clear
• By exchanging A-factors, direction of PT can be
  reversed

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Recommendation

• As at present, approach would remain supported by
  cost-benefit analysis
• If existing SQSS approach is to be retained,
  adopt Approach 1(b)
• Different (but constant) A-factors in exporting
  and importing areas (AT 0.72 or 0.05)