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Transcript of – Workshop 3 – Birmingham, 10 January 2008 Current GB SQSS Approach Cornel Brozio Scottish Power...
– Workshop 3 –Birmingham, 10 January 2008
Current GB SQSS Approach
Cornel Brozio
Scottish Power EnergyNetworks
This Presentation
Overview of current SQSS methodology
Interpretation of Planned Transfer and Required Transfer
Variations on SQSS approach
Comparison and Conclusions
Approach 1 - SQSS Methodology
a) Current method with wind AT = 0.72 Section 1.1, Appendix 3
b) Different exporting and importing area wind AT (0.72/0.05)
Section 1.3.1
c) Variable wind A-factors Section 1.3.2, Appendix 4
Current SQSS Methodology
Transmission boundary capability at ACS peak
Planned Transfer (Appendix C of SQSS)
Interconnection Allowance (Appendix D of SQSS)
Required Capacity = PT+IA
1(a) – 1
Setting up Planned Transfer
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
1(a) – 2
Ranking Order Example
Unit or Module
Registered Capacity (MW)
Contribution to Plant Margin
(MW)
Cumulative Capacity (MW)
Unit 1 500 500 500
Windfarm A 600 0.4 600 = 240 740
Windfarm B 200 0.4 200 = 80 820
. . . . . . . . .
Unit J 200 200 71900
Unit K 200 200 72100
Unit L 100 100 72200
For ACS demand of 60GW
Less
like
ly t
o ru
n
1(a) – 3
WindWindet RLRA
Wind Equivalent in Ranking Order
Average availabilityof a thermal unit
(At 0.9)
Registered capacity ofequivalent thermal unit
Wind generation winter load factor (LWind 0.36)
Wind generationregisteredcapacity
Average P available from equivalent
thermal unit
Average P available from wind generation
Re = 0.4 RWind
1(a) – 4
Straight Scaling
Power output of generator i of type T
PTi = S AT RTi
Availability atACS peak
Registeredcapacity
Match generationand demand
(Applies to entire network)
With a plant margin of 20% and AT = 1.0, S = 0.833
1(a) – 5
Availability Factors
SQSS does not prescribe AT values Thermal and hydro units:
AT = 1.0
Wind generation: AT = 0.72
PT in 833021
1.
.TiP
PT in 6072021
1.
..
TiP
1(a) – 6
Planned Transfer Example
AREA 1
AREA 2
RTi = 10000 MWD1 = 6000 MWG1 = 8333 MW
RTi = 62000 MWD2 = 54000 MWG2 = 51667 MW
PT = 2333 MW
System in Planned Transfer conditionTotal ACS peak demand = 60GW
1(a) – 7
Interconnection Allowance
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
1(a) – 8
Circle Diagram
)(2 21
11
DD
GD
1(a) – 9
IA Application Example
AREA 1
AREA 2
RTi = 10000 MWD1 = 6000 MWG1 = 8333 MW
RTi = 62000 MWD2 = 54000 MWG2 = 51667 MW
PT = 2333 MW
System in Planned Transfer condition
%9.11600002
83336000
)(2 21
11
DD
GD
Circle diagramx-axis:
y-axis: 2.1%IA = 1260 MW
1(a) – 10
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, assuming Enough generation in the exporting area No local constraints
PT PT + IAPT + ½IA
Expected boundarytransfer at ACS peak
Actual Boundary TransferF
requ
ency
BoundaryTransfer
Variations Considered for Wind
Keep PT+IA and PT+½IA 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
Different Export and Import Wind A-factors
PT+½IA 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
1(b) – 1
Importing Wind A-factor
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)
1(b) – 2
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 PT+IA (N-1) matches P99 and PT+½IA (N-2) matches P95
with minimum error.
Exporting Area Wind A-Factor
y = -0.5706x + 0.8657
0.0
0.2
0.4
0.6
0.8
1.0
1.2
-0.2 0 0.2 0.4 0.6 0.8 1 1.2
Difference between conventional and wind generation capacity in the exporting area in p.u. on system demand
Win
d A
-fac
tor
in e
xpo
rtin
g a
rea
(AW
E)
Demand System Total
Generation Wind- Generation alConvention
Win
d A
-Fac
tor
1(c) – 2
Importing Area Wind A-Factor
y = -0.0261x + 0.0593
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
0 0.2 0.4 0.6 0.8 1 1.2
Difference between conventional and wind generation capacity in the importing area in p.u. on system demand
Win
d A
-fac
tor
in im
po
rtin
g a
rea
(AW
I)
Demand System Total
Generation Wind- Generation alConvention
Win
d A
-Fac
tor
1(c) – 3
Results for 2007/8
2007/8
0
2000
4000
6000
8000
10000
12000
14000
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
Boundary
Req
uir
ed B
ou
nd
ary
Cap
acit
y (M
W)
0.72/0.72
0.72/0.05
Variable
RT
(M
W)
Results for 2020/1
2020/21
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
Boundary
Req
uir
ed B
ou
nd
ary
Cap
acit
y (M
W)
0.72/0.72
0.72/0.05
Variable
RT
(M
W)
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
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
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)