available transfer capability determination
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Third NSF Workshop on US-Africa Research and Education Collaboration Abuja, Nigeria, December 13-15, 2004. Available Transfer Capability Determination. Chen-Ching Liu and Guang Li University of Washington. Overview. Background of Available Transfer Capability (ATC) Definitions of ATC - PowerPoint PPT PresentationTRANSCRIPT
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Available Transfer Capability Determination
Chen-Ching Liu and Guang LiUniversity of Washington
Third NSF Workshop on US-Africa Research and Education Collaboration
Abuja, Nigeria, December 13-15, 2004
TECHNOLOGY &
ENVIRONMENT
ENERGY &
EDUCATION
TECHNOLOGY &
ENVIRONMENT
ENERGY &
EDUCATION
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Third US-Africa Research and
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Overview
• Background of Available Transfer Capability (ATC)
• Definitions of ATC• Determination of ATC• Examples of ATC in Nigerian NEPA 330kV Grid• Optimization Technique to Calculate ATC• Stability-Constrained ATC Calculation Method• Conclusions
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Background
• ATC is the transmission limit for reserving and scheduling energy transactions in competitive electricity markets.
• Accurate evaluation of ATC is essential to maximize utilization of existing transmission grids while maintaining system security.
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Transmission Service Types
• Recallable transmission service: Transmission service that a transmission provider can interrupt in whole or in part.
• Non-recallable transmission service: Transmission service that cannot be interrupted by a provider for economic reasons, but that can be curtailed for reliability.
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ATC Under Operating Constraints
• Transfer capability must be evaluated based on the most limiting factor.
Time
Voltage Limit
Stability LimitPower Flow A to B (MW)
Thermal Limit
Total Transfer Capability
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Available Transfer Capability (ATC) (North American Electric Reliability Council)
MW A->B
TimeOperating Horizon Planning Horizon
Nonrecallable Scheduled
Recallable Scheduled
Nonrecallable Reserved
Recallable Reserved
Total TransferCapability (TTC)Transmission
Reliability Margin
TRM
TRM
Nonrecallable Reserved
Nonrecallable Available Transfer
Capability
Nonrecallable ATC
ATCRecallable
Recallable ATC
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Definition of ATC
• ATC = TTC – TRM – Existing Transmission Commitments (including CBM)
• Transmission Transfer Capability Margins– Transmission Reliability Margin (TRM)– Capacity Benefit Margin (CBM)
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Transmission Reliability Margin (TRM)
• Uncertainty exists in future system topology, load demand and power transactions
• TRM is kind of a safety margin to ensure reliable system operation as system conditions change.
• TRM could be 8% or 10% of the TTC
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Capacity Benefit Margin (CBM)
• CBM is reserved by load serving entities to ensure access to generation from interconnected systems to meet generation reliability requirements.
• Intended only for the time of emergency generation deficiencies
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State of the Art: ATC Methods
ATC MethodsATC Methods DescriptionDescription
Linear Approximation MethodDC Power Flow Model,
Thermal Limit Only
Optimal Power Flow Method AC Power Flow Model, Thermal Limit + Voltage Limit
Continuation Power Flow MethodAC Power Flow Model,
Thermal Limit + Voltage Limit (Voltage Collapse)
Stability-Constrained ATC Method Time Domain Simulations with Dynamic Model
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First Contingency Incremental Transfer Capability (FCITC) & First Contingency Total
Transfer Capability (FCTTC)
FCTTC
FCITC
BASE POWER TRANSFERS
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Total Transfer Capability (TTC)
• System Conditions
• Critical Contingencies
• Parallel Path Flows
• Non-Simultaneous and Simultaneous Transfers
• System Limits
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Procedure to Calculate TTC
• Start with a base case power flow• Increase generation in area A and increase
demand in area B by the same amount• Check the thermal, stability and voltage
constraints.• Evaluate the first contingency event and ensure
that the emergency operating limits are met.• When the emergency limit is reached for a first
contingency, the corresponding (pre-contingency) transfer amount from area A to area B is the TTC.
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Example 1: 2-Area NEPA 330kV Grid
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2-Area Base-Case Tie Flow
21 23
Area 1
4.64 MW
Area 2
No thermal limit (assumed 120% base case flow) reached
Single transmission line contingency
First thermal limit reached
Notation
Tie Line Flow
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Area 1 to Area 2 ATC Calculation
21 23
Area 1
> 4.64 MW
Area 2
Increasing
Generation
P MW
Increasing
Demand
P MW
21 23
Area 1
4.96 MW
Area 2
7-25
2-8
Increased
Generation
0.32 MW
Increased
Demand
0.32 MW
FCITC
FCTTC
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Area 2 to Area 1 ATC Calculation
21 23
Area 1
< 4.64 MW
Area 2
Increasing
Demand
P MW
Increasing
Generation
P MW
21 23
Area 1
4.54 MW
Area 2
7-25
5-24
Increased
Demand
0.1 MW
Increased
Generation
0.1 MW
FCITC
FCTTC
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2-Area ATC Calculation
Direction Area 1 to Area 2 Area 2 to Area 1
Critical Contingency
Line 7-25 (Delta-Aladja)
Line 7-25 (Delta-Aladja)
Thermal Limit
Reached
Line 2-8 (Jebba G.S.-Jebba T.S.)
Line 5-24 (Alam-Aba)
FCTTC 4.96 MW 4.54MW
FCITC 0.32 MW 0.1 MW
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Example 2: 4-Area NEPA 300kV Grid
AREA 1
AREA 2
AREA 3
AREA 4
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4-Area Base-Case Tie Flows
Area 1
4.64 MW
Area 2Area 4
16.6 MW
Area 3
8.24 MW8.5 MW
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Area 3 to Area 1 ATC calculation (Example of Parallel Path Flows)
Area 1
4.64 MW
Area 2Area 4
17.2 MW
Area 3
8.65 MW9.1 MW
7-25
1-7
Increased Generation 1.01 MW
Increased Demand 1.01 MW
FCTTC = 9.1+ 8.65 = 17.75 MW
FCITC = 17.75 (8.5 + 8.24) = 1.01 MW
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Area 4 to Area 2 Simultaneous ATC with a Pre-existing Area 3 to Area 1 17.75 MW Transfer
Area 1
4.85 MW
Area 2Area 4
16.99 MW
Area 3
8.65 MW9.1 MW
7-25
4-10
Increased Generation 0.21 MW
Increased Demand 0.21 MW
FCTTC = 16.99 (17.2) = 0.21 MW
FCITC = 4.85 4.64 = 0.21 MW
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Optimization Technique to Calculate ATC
A area
maxi
iΔP
0),(
),(
0
),(0
),(
maxmin
maxmax
max
yxEM
VVV
FyxFF
PPP
yxg
yxfx
iii
Objective:
Subject to
sum of generation in sending area A
- system dynamic behavior
- power flow equations
- active power output
- thermal limit
- voltage profile
- energy margin
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Stability-Constrained ATC
Second-Kick based Energy Margin Computation
Second-Kick based Energy Margin Computation
Time Domain Simulation (ETMSP)
System trajectory
No
Energy Margin Sensitivity Analysis with BFGS Method
Energy Margin Sensitivity Analysis with BFGS Method
Generation AdjustmentGeneration Adjustment
(EM = 0) ?(EM = 0) ?
Yes
ATCATC
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Second-kick-based energy margin computation
Perform time-domain simulation
Obtain system trajectory following a pre-specified disturbance sequence
Compute potential energy of first- and second-kick trajectories
Potential energy difference at the respective peaksof the first- and second-kick disturbances
- Simulation
- Trajectory
- Potential energy
- Energy margin
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Energy margin sensitivity computation
• Determine the search direction with the Broyden-Fletcher-Goldfarb-Shanno (BFGS) method
D is an approximation to the inverse of Hessian matrix
)(,
)(1,
)(
)(
)(1
)(
knm
km
k
kn
k
k
P
EM
P
EM
D
S
S
S
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Generation adjustment
nm
m
pkn
kn
kk
nm
m
P
P
kEM
S
S
P
P
,
1,
1)()(
1)(1
)(1
,
1,
nm
m
oldnm
oldm
newnm
newm
P
P
P
P
P
P
,
1,
,
1,
,
1,
- Adjustment
- Update
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2-Area Test System
120 110 11
12
13
101 1
3
2
10 20 G1
G2 G12
G11
• Net power transferred from area A to area B in the base case = 453 MW
453 MWArea A Area B
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Stability-Constrained ATC Results
Power Transfer
(Area AArea B) & Energy Margin
Gen.
453 MW G1 666 1.9008 1.9008 0.5333 3.745EM = 13.35 G2 754 1.4688 1.4688 0.4667 4.242
461 MW G1 669.745 1.1483 1.1483 0.5161 4.935EM = 10.98 G2 758.242 0.9503 0.9503 0.4838 5.59471.6 MW G1 674.68 0.4748 1.4562 0.3757 2.833EM = 5.50 G2 763.832 0.0864 2.136 0.6242 3.208
G1 677.51 -1.417G2 767.04 -1.604
474.6 MW G1 676.094 1.8204 1.8204 0.4809 0.587EM = 2.22 G2 765.436 1.7345 1.7345 0.5191 0.665475.8 MW G1 676.681 2.4251 2.4251 0.5125 0.047EM = 0.22 G2 766.101 2.0364 2.0364 0.4875 0.054
(MW)
1
2
4 477.6 MW EM = N/A
System goes unstable with
the 1st kick disturbance.
(MW)
5
6
Iteration
3
kmP ,
kmP
EM
,
ksk kmP ,
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Conclusions
• ATC provides a reasonable and dependable indication of available transfer capabilities in electric power markets.
• ATC considers reasonable uncertainties in system conditions and provides operating flexibility for the secure operation of the interconnected network.
• The effects of simultaneous transfers and parallel path flows are studied.
• Need for ATC calculation method to incorporate voltage, angle stability limits as well as thermal limits.
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References
[1] North American Electric Reliability Council, “Available Transfer Capability Definitions and Determination”, June 1996.
[2] North American Electric Reliability Council,“Transmission Transfer Capability”, May 1995.
[3] S. K. Joo, C. C. Liu, Y. Shen, Z. Zabinsky and J. Lawarree, “Optimization Techniques for Available Transfer Capability (ATC) and Market Calculations,” IMA Journal of Management Mathematics (2004) 15, 321-337.