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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

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available transfer capability determination

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
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

Third US-Africa Research and Education Collaboration Workshop

Abuja, Nigeria, December 13-15, 2004

background
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.

Third US-Africa Research and Education Collaboration Workshop

Abuja, Nigeria, December 13-15, 2004

transmission service types
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.

Third US-Africa Research and Education Collaboration Workshop

Abuja, Nigeria, December 13-15, 2004

atc under operating constraints

Power Flow

A to B (MW)

Stability Limit

Voltage Limit

Thermal Limit

Total Transfer Capability

Time

ATC Under Operating Constraints
  • Transfer capability must be evaluated based on the most limiting factor.

Third US-Africa Research and Education Collaboration Workshop

Abuja, Nigeria, December 13-15, 2004

available transfer capability atc north american electric reliability council

MW

Total Transfer

Capability (TTC)

A->B

TRM

Transmission

Reliability Margin

Nonrecallable

TRM

ATC

Recallable

ATC

Recallable

Nonrecallable

ATC

Available

Transfer

Recallable

Capability

Recallable

Scheduled

Reserved

Nonrecallable

Reserved

Nonrecallable

Nonrecallable

Reserved

Scheduled

Time

Operating Horizon

Planning Horizon

Available Transfer Capability (ATC) (North American Electric Reliability Council)

Third US-Africa Research and Education Collaboration Workshop

Abuja, Nigeria, December 13-15, 2004

definition of atc
Definition of ATC
  • ATC = TTC – TRM – Existing Transmission Commitments (including CBM)
  • Transmission Transfer Capability Margins
    • Transmission Reliability Margin (TRM)
    • Capacity Benefit Margin (CBM)

Third US-Africa Research and Education Collaboration Workshop

Abuja, Nigeria, December 13-15, 2004

transmission reliability margin trm
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

Third US-Africa Research and Education Collaboration Workshop

Abuja, Nigeria, December 13-15, 2004

capacity benefit margin cbm
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

Third US-Africa Research and Education Collaboration Workshop

Abuja, Nigeria, December 13-15, 2004

state of the art atc methods

ATC Methods

Description

DC Power Flow Model, Thermal Limit Only

Linear Approximation Method

AC Power Flow Model, Thermal Limit + Voltage Limit (Voltage Collapse)

Continuation Power Flow Method

AC Power Flow Model, Thermal Limit + Voltage Limit

Optimal Power Flow Method

Time Domain Simulations with Dynamic Model

Stability-Constrained ATC Method

State of the Art: ATC Methods

Third US-Africa Research and Education Collaboration Workshop

Abuja, Nigeria, December 13-15, 2004

slide11
First Contingency Incremental Transfer Capability (FCITC) & First Contingency Total Transfer Capability (FCTTC)

FCITC

FCTTC

BASE POWER

TRANSFERS

Third US-Africa Research and Education Collaboration Workshop

Abuja, Nigeria, December 13-15, 2004

total transfer capability ttc
Total Transfer Capability (TTC)
  • System Conditions
  • Critical Contingencies
  • Parallel Path Flows
  • Non-Simultaneous and Simultaneous Transfers
  • System Limits

Third US-Africa Research and Education Collaboration Workshop

Abuja, Nigeria, December 13-15, 2004

procedure to calculate ttc
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.

Third US-Africa Research and Education Collaboration Workshop

Abuja, Nigeria, December 13-15, 2004

example 1 2 area nepa 330kv grid
Example 1: 2-Area NEPA 330kV Grid

Third US-Africa Research and Education Collaboration Workshop

Abuja, Nigeria, December 13-15, 2004

2 area base case tie flow
2-Area Base-Case Tie Flow

Single transmission line contingency

Notation

No thermal limit (assumed 120% base case flow) reached

First thermal limit reached

4.64 MW

Tie Line Flow

21

23

Area 1

Area 2

Third US-Africa Research and Education Collaboration Workshop

Abuja, Nigeria, December 13-15, 2004

area 1 to area 2 atc calculation
Area 1 to Area 2 ATC Calculation

> 4.64 MW

Increasing

Generation

DP MW

Increasing

Demand

DP MW

21

23

Area 1

Area 2

Increased

Demand

0.32 MW

Increased

Generation

0.32 MW

4.96 MW

7-25

21

23

2-8

FCTTC

Area 1

Area 2

FCITC

Third US-Africa Research and Education Collaboration Workshop

Abuja, Nigeria, December 13-15, 2004

area 2 to area 1 atc calculation
Area 2 to Area 1 ATC Calculation

< 4.64 MW

Increasing

Demand

DP MW

Increasing

Generation

DP MW

21

23

Area 1

Area 2

Increased

Generation

0.1 MW

Increased

Demand

0.1 MW

4.54 MW

21

23

5-24

7-25

FCTTC

Area 1

Area 2

FCITC

Third US-Africa Research and Education Collaboration Workshop

Abuja, Nigeria, December 13-15, 2004

2 area atc calculation
2-Area ATC Calculation

Third US-Africa Research and Education Collaboration Workshop

Abuja, Nigeria, December 13-15, 2004

example 2 4 area nepa 300kv grid
Example 2: 4-Area NEPA 300kV Grid

AREA 1

AREA 3

AREA 2

AREA 4

Third US-Africa Research and Education Collaboration Workshop

Abuja, Nigeria, December 13-15, 2004

4 area base case tie flows
4-Area Base-Case Tie Flows

Area 1

8.5 MW

8.24 MW

16.6 MW

4.64 MW

Area 4

Area 3

Area 2

Third US-Africa Research and Education Collaboration Workshop

Abuja, Nigeria, December 13-15, 2004

area 3 to area 1 atc calculation example of parallel path flows
Area 3 to Area 1 ATC calculation (Example of Parallel Path Flows)

Area 1

FCTTC = 9.1+ 8.65 = 17.75 MW

FCITC = 17.75  (8.5 + 8.24) = 1.01 MW

Increased Demand 1.01 MW

9.1 MW

8.65 MW

17.2 MW

4.64 MW

1-7

7-25

Increased Generation 1.01 MW

Area 4

Area 3

Area 2

Third US-Africa Research and Education Collaboration Workshop

Abuja, Nigeria, December 13-15, 2004

area 4 to area 2 simultaneous atc with a pre existing area 3 to area 1 17 75 mw transfer
Area 4 to Area 2 Simultaneous ATC with a Pre-existing Area 3 to Area 1 17.75 MW Transfer

Area 1

FCTTC = 16.99  (17.2)= 0.21 MW

FCITC = 4.85  4.64 = 0.21 MW

9.1 MW

8.65 MW

Increased Generation 0.21 MW

16.99 MW

4.85 MW

4-10

Increased Demand 0.21 MW

7-25

Area 4

Area 3

Area 2

Third US-Africa Research and Education Collaboration Workshop

Abuja, Nigeria, December 13-15, 2004

optimization technique to calculate atc
Optimization Technique to Calculate ATC

sum of generation in sending area A

Objective:

- system dynamic behavior

- power flow equations

Subject to

- active power output

- thermal limit

- voltage profile

- energy margin

Third US-Africa Research and Education Collaboration Workshop

Abuja, Nigeria, December 13-15, 2004

stability constrained atc

Time Domain Simulation

(ETMSP)

System trajectory

Second-Kick based Energy Margin Computation

Yes

(EM = 0) ?

ATC

No

Energy Margin Sensitivity Analysis with BFGS Method

Generation Adjustment

Stability-Constrained ATC

Third US-Africa Research and Education Collaboration Workshop

Abuja, Nigeria, December 13-15, 2004

second kick based energy margin computation
Second-kick-based energy margin computation

Perform time-domain simulation

- Simulation

Obtain system trajectory following a pre-specified

disturbance sequence

- Trajectory

Compute potential energy of first- and

second-kick trajectories

- Potential energy

Potential energy difference at the respective peaks

of the first- and second-kick disturbances

- Energy margin

Third US-Africa Research and Education Collaboration Workshop

Abuja, Nigeria, December 13-15, 2004

energy margin sensitivity computation
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

Third US-Africa Research and Education Collaboration Workshop

Abuja, Nigeria, December 13-15, 2004

generation adjustment
Generation adjustment

- Adjustment

- Update

Third US-Africa Research and Education Collaboration Workshop

Abuja, Nigeria, December 13-15, 2004

2 area test system

Net power transferred from area A to area B in the base case = 453 MW

Area B

Area A

453 MW

2-Area Test System

Third US-Africa Research and Education Collaboration Workshop

Abuja, Nigeria, December 13-15, 2004

stability constrained atc results
Stability-Constrained ATC Results

Third US-Africa Research and Education Collaboration Workshop

Abuja, Nigeria, December 13-15, 2004

conclusions
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.

Third US-Africa Research and Education Collaboration Workshop

Abuja, Nigeria, December 13-15, 2004

references
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.

Third US-Africa Research and Education Collaboration Workshop

Abuja, Nigeria, December 13-15, 2004