Presentation on theme: "Current GB SQSS Approach"— Presentation transcript:
1 Current GB SQSS Approach Cornel BrozioScottish Power EnergyNetworks– Workshop 3 –Birmingham, 10 January 2008
2 This Presentation Overview of current SQSS methodology Interpretation of Planned Transfer and Required TransferVariations on SQSS approachComparison and ConclusionsOverview of the approach followed presently.Something about PT and RT and what they mean.Know that current method is limited – considered how it could be adapted or modified to work better for wind.Results from variations and comparison.
3 Approach 1 - SQSS Methodology Current method with wind AT = 0.72Section 1.1, Appendix 3Different exporting and importing area wind AT (0.72/0.05)Section 1.3.1Variable wind A-factorsSection 1.3.2, Appendix 4These variations are:Called approaches 1(a), (b) and (c).Link to report sections.
4 Current SQSS Methodology 1(a) – 1Current SQSS MethodologyTransmission boundary capability at ACS peakPlanned Transfer (Appendix C of SQSS)Interconnection Allowance (Appendix D of SQSS)Required Capacity = PT+IAApproach 1(a)MITS requirements at ACS peakBoundary splitting system into two parts – transmission capacity across this boundary.PT refers to a system (at winter peak) with PM <= 20% and generation scaled to meet demand.2-Stage process: PT and IA
5 Setting up Planned Transfer Ranking Order techniqueSet Plant Margin 20%Assumption is that market will deliver around 20%, but many closures are unknownPlant least likely to run is treated as non-contributoryStraight Scaling techniqueScale generation to meet demandScaling proportional to availability at time of ACS peakPT refers to a system (at winter peak) with PM <= 20% and generation scaled to meet demand.Scaling sets up PT condition.PT now exists on any circuit or boundary in the network.
6 Ranking Order Example For ACS demand of 60GW Less likely to run Unit or ModuleRegistered Capacity (MW)Contribution to Plant Margin (MW)Cumulative Capacity (MW)Unit 1500Windfarm A6000.4 600 = 240740Windfarm B2000.4 200 = 80820. . .Unit J71900Unit K72100Unit L10072200Less likely to run
7 Wind Equivalent in Ranking Order Average P available from equivalent thermal unitAverage P available from wind generationWind generationregisteredcapacityAverage availabilityof a thermal unit(At 0.9)Convert each wind farm, or group of wind farms, to an equivalent thermal unit.Equivalent thermal unit has same average power availability as wind generation.Assume wind will always run at maximum available power, therefore, average available power = load factor (in winter).Divide by thermal available power to convert to equivalent thermal unit (full registered capacity is used in ranking order).Mention that 36% is based on data measured in Southern Scotland. Load factors were:Winter: 36%Summer: 23%Year: 30%Registered capacity ofequivalent thermal unitWind generation winter load factor (LWind 0.36)Re = 0.4 RWind
8 (Applies to entire network) Straight Scaling1(a) – 5Power output ofgenerator i of type TRegisteredcapacityPTi = S AT RTiMatch generationand demand(Applies to entire network)Availability atACS peakApply when PM has been reduced to <= 20% by ranking order technique.All contributory generation is scaled.Imports/exports like France or NIE are ignored here. However, they are not scaled, but are treated as demand (Pos = export, Neg = import).If all AT are the same, its value does not matter; S x AT will be the same.S = 1/1.2 = 0.833With a plant margin of 20% and AT = 1.0, S = 0.833
9 Availability Factors SQSS does not prescribe AT values Thermal and hydro units:AT = 1.0Wind generation:AT = 0.72Sometimes hydro AT = 0.96 (P 0.80 in PT)If plant margin is exactly 20%…
10 Planned Transfer Example RTi = MWD1 = 6000 MWG1 = 8333 MWAREA 1PT = 2333 MWAREA 2 RTi = MWD2 = MWG2 = MWPT would now exist on any boundary.PM = 20%, so S = and total generation is 72GW.PM (North) = 67%, PM (South) = 14.8%** Shown how PT is set up, now moving on to application of IA.System in Planned Transfer conditionTotal ACS peak demand = 60GW
11 Interconnection Allowance Planned Transfer condition set upSelect boundary, i.e. split system into two partsFind IA from the ‘Circle Diagram’Boundary capability:PT + IA for N-1PT + ½IA for N-2 or N-DApplying IA to the system.Steps to set up system with IA or IA/2.Under these conditions, for secured event (N-1, N-2, busbar, mesh corner),there may not beloss of demandunacceptable overloadingvoltages outside limitssystem instability
12 1(a) – 9Circle DiagramOrigins a bit hazy, but reported to be based on observed transfers in the 1940’s.Reviewed in early 1990’s and found to still be appropriate for system.See appendix D in SQSS.Total ACS peak demand = D1+D2D1+G1 = Dem+Gen in small area (Area 1 in example).
13 IA Application Example Circle diagramx-axis:RTi = MWD1 = 6000 MWG1 = 8333 MWAREA 1PT = 2333 MWAREA 2 RTi = MWD2 = MWG2 = MWFind IA from circle diagramN-1: 3593MWN-2: 2963MWy-axis: 2.1%IA = 1260 MWSystem in Planned Transfer condition
14 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 (PT+½IA) can be met for 95% of actual generation and demand outcomes at ACS peak, assumingEnough generation in the exporting areaNo local constraints
15 Actual Boundary Transfer PTPT + IAPT + ½IAFrequencyPT is the median transfer. Depending on actual demand and generation outcomes, the boundary transfer could be higher or lower (even negative).PT+IA/2 gives around P95 (but, N-2/D less likely than N-1)PT+IA gives around P99 (but, more likely than N-2/D)Wind will change the shape/parameters of the distribution – we want to keep N-1 and N-2 probabilities/percentiles constant.With wind, PT and the shape of the distribution will be different, but we want to approximately maintain PT+IA/2 at P95 and PT+IA at P99.BoundaryTransferExpected boundarytransfer at ACS peak
16 Variations Considered for Wind Keep PT+IA and PT+½IA at same percentile of possible boundary transfersProbabilities of exceeding N-1 or N-2 capabilities remain broadly constantVariations considered:Approach 1(b): Different wind A-factors for importing and exporting areasApproach 1(c): Variable wind A-factors based on wind volumes in each area
17 Different Export and Import Wind A-factors 1(b) – 1PT+½IA captures all but the highest 5% of boundary transfersWhen imbalance in available power is highestShould include imbalance due to wind conditionsAt 60% in PT, support from wind generation in importing area is over-estimatedApproach 1(b)We are trying to capture the high 5-10% of transfers where available power in Area 1 is much higher than the available power in Area 2. I.e. when the imbalance in available power is highest. This should include imbalance due to wind conditions.An important side effect of this is that the PT now becomes boundary dependent, i.e. a different PT needs to be set up for each boundary to study.
18 Importing Wind A-factor 1(b) – 2Importing Wind A-factorIn exporting area 60% is approximately P90 of wind output‘Mirror’ exporting area by using P10 of wind generator power output:About 4% of rated capacityAT = 0.05 (around 0.05 = 0.04 in PT)Approach 1(b)Different (but constant) A-factorsExporting area AT = 0.72 for wind (60% in PT)Importing area AT = 0.05 for wind (4% in PT)
19 Approach 1(c): Variable Wind A-factors Aims to find A-factors as functions of relative wind generation volumes for any boundaryMonte-Carlo simulation to find distribution of transfers and find P99 and P95Using SQSS approach for same boundary, adjust wind A-factors untilPT+IA (N-1) matches P99 andPT+½IA (N-2) matches P95with minimum error.Consider a particular boundary.Assumption is that N-1 P99 and N-2 P95.Simulation was carried out for all boundaries.Simplified simulation was used to determine A-factor functions; these were then applied to scenario.
24 Summary Approach 1(a) – Single A-factor (0.72) Works well, but over-estimates wind contribution in importing areaApproach 1(b) - Different A-factors (0.72/0.05)Extends existing approachSystem security remains broadly constantI.e. probability of exceeding N-1 or N-2 capability remains approximately constantApproach 1(c) - Variable A-factorsDifficult to find robust A-factor functions (scatter on graphs)Additional complexityExcept high-wind export boundaries, very similar RT to constant 0.72/0.05For high-wind boundaries, economics are very likely to justify more transmission.
25 Drawback - Different PT for each Boundary Both variations of SQSS approach mean that PT becomes boundary dependentDifferent A-factors in each areaSingle PT condition no longer existsImporting and exporting areas not always clearBy exchanging A-factors, direction of PT can be reversedApproaches 1(b) and (c)
26 RecommendationAs at present, approach would remain supported by cost-benefit analysisIf 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)