9 April 2002

Small Signal Stability Analysis Study:

study prepared by Powertech Labs Inc. for ERCOT

Vance Beauregard

AEP

9 April 2002

Small Signal Stability

Power System Stability

Angle Stability Frequency Stability Voltage Stability

Transient StabilityLarge DisturbanceVoltage Stability

Small DisturbanceVoltage Stability

Short Term Short TermLong Term Long Term

Small Signal StabilitySmall Signal

Stability

Power System StabilityPower System Stability

Angle StabilityAngle Stability Frequency StabilityFrequency Stability Voltage StabilityVoltage Stability

Transient StabilityTransient StabilityLarge DisturbanceVoltage Stability

Large DisturbanceVoltage Stability

Small DisturbanceVoltage Stability

Small DisturbanceVoltage Stability

Short TermShort Term Short TermShort TermLong TermLong Term Long TermLong Term

Classification Of Power System Stability

9 April 2002

Eigenvalue And Stability

• Stability of the linearized system is described by the eigenvalues of the state matrix

• A real eigenvalue, or a pair of complex eigenvalues, is usually referred to as a mode

• For a complex mode =j, two quantities are of main interest:

Frequency (in Hz)

Damping ratio (in %)

• The system is unstable if is negative

To ensure the acceptable performance, a damping margin in the range of 3%-5% is normally required

2

f

22100

9 April 2002

Modal Characteristics

• While an eigenvalue indicates the stability, its right and left eigenvectors give much more information on the characteristics of the mode

• The right eigenvector shows the mode shape, i.e., the observability of the mode

A mode should be observable from generator rotor oscillations if the generator is high in its mode shape

• A weighted left eigenvector shows the participation factors, i.e., the controllability of the mode

A mode should be controllable from generator if the generator is high in its participation factors

• A generator which is high in the mode shape of a mode is not necessarily high in the participation factor of the same mode

9 April 2002

Powertech’s Approach

• To perform a comprehensive small signal stability study on the ERCOT system

Overall system performance assessment from a modal perspective Optimal tuning for new or existing PSS to provide the best damping Results fully verified by time-domain simulations

• To assess multiple scenarios to ensure the robustness of the recommended control settings

Load levels Generation dispatches Transmission configurations

• To incorporate appropriate study criteria

Contingencies Damping criteria

9 April 2002

Task 6 – Tuning Of Controls

• Only generator controls (mainly AVR and PSS) will be considered for tuning

• Tuning will be performed for the worst cases identified in Task 5

Generators to be tuned will be determined by the participation factors Parameters of the existing controls will be tuned for best damping New PSS will be recommended to provide additional damping if necessary Tuning will be based on the damping criteria set in Task 2

• A combination of the following methods will be used to derive the optimal setting of the control parameters:

Phase compensation Sensitivity analysis Eigenvalue analysis

• The performance of the tuned controls will be verified by time-domain simulations

9 April 2002

Project Objectives

• Examination of the small signal stability of the ERCOT interconnected system, particularly the sensitivities of the critical system modes with respect to different loading, transfer levels, system configurations, and contingencies.

• Tuning of the power system stabilizers (PSS) in the ERCOT area so as to provide optimal damping for the critical modes

• This project is focused only on small signal (oscillatory) stability; other types of system security concerns (such as transient stability or voltage stability) are not examined

9 April 2002

Data Assembly

• Four base models were provided by ERCOT

2001 light load 2001 peak load 2004 light load 2004 peak load All at market transfer

• Major data modifications/updates

Generator parameter updates to fix limit violation problems during initialization of the models

Addition of 4 Sand Hill PSS Addition of 18 AEP PSS

• 18 AEP PSS were not included in most studies as they were provided very late in the project

Some benchmarking was made to show the impact of these PSS These PSS have been tuned in a previous project by Powertech

9 April 2002

Creation of Study Scenarios

• High transfer scenarios

7 high transfer scenarios for each loading condition

Total 32 scenarios - including the marketing (base) transfer scenarios

West-east

East-West North-south

South-North

South-Rio Grande valley

Rio Grande valley-south

From-Houston

Target transaction amount for each transfer may not be reached in the final scenario because of generation availability and powerflow solution

9 April 2002

Creation of Study Scenarios (Cont’d)

• Configuration change scenarios

Used only to examine the sensitivities of the critical modes to some transmission enhancement projects expected to complete by 2004

Constructed based on the 2004 peak load high south-north transfer scenario

• The following projects were removed from the base model individually

Morgan Creek-Twin Buttes-Red Creek-Comanche Switch 345 kV Line Graham-Jacksboro 345 kV Line San Miguel-Pawnee-Coleto Creek 345 kV Line Monticello-Farmersville-Valley Junction-Anna Switch 345 kV Line (powerflow does

not converge) Venus-Liggett 345 kV Line Anna Switch-Collin-NW Carrollton 345 kV Line Upgrade

• 5 scenarios were created

9 April 2002

North-South Mode

• Summary of the mode

• Mode shape

Loading level Frequency range (Hz) Damping range (%) Scenario with least damping2001 light load 0.7782 to 0.8810 2.17 to 9.45 High south-north transfer2001 peak load 0.5181 to 0.6484 -2.32 to 8.31 High south-north transfer2004 light load 0.7174 to 0.8635 1.54 to 8.42 High south-north transfer2004 peak load 0.5557 to 0.6189 -0.20 to 9.16 High south-north transfer

9 April 2002

East-West Mode

• Summary of the mode

• Mode shape

Loading level Frequency range (Hz) Damping range (%) Scenario with least damping2001 light load 0.8353 8.86 High east-west transfer

Damping in other scenarios is larger than 10%2001 peak load 0.6545 to 0.8750 1.75 to 7.25 High Rio Grande valley-south transfer2004 light load 0.8428 6.25 High east-west transfer

Damping in other scenarios is larger than 10%2004 peak load 0.6742 to 0.8184 2.57 to 9.17 High from-Houston transfer

9 April 2002

Center-North/South Mode

• Summary of the mode

• Mode shape

Loading level Frequency range (Hz) Damping range (%) Scenario with least damping2001 light load N/A N/A N/A2001 peak load 0.9278 to >1.0 2.41 to >10.0 High south-north transfer2004 light load N/A N/A N/A2004 peak load 0.9587 to >1.0 5.64 to >10.0 High from-Houston transfer

9 April 2002

Critical Contingencies

• Selected from the worst N-1 and N-2 contingencies

• Applied to all 32 scenarios for PSS tuning verification

No. Outaged circuits(s)1 S. Texas Project Plant – Whitepoint2 Pawnee – Lon Hill 3453 Dow-Velasco 345 – S. Texas Project Plant (double lines)4 San Miguel – Miguel 55 Marion – San Miguel (double lines)6 J.K. Spruce – Pawnee7

8

9

10

Lon Hill 345 – Coleto CreekLon Hill 138 – Medio Creek

Lon Hill 345 – Lon Hill/N. Edinburg Comp S1Lon Hill 138 – Orange Grove

Dow-Velasco 345 – W.A. Parish C710Dow-Velasco 345 – W.A. Parish 5

Coleto Creek – Lon Hill 345Goliad – Fannin

9 April 2002

Analysis of the Configuration Change Scenarios

• Two main inter-area modes were compared

The transmission project in southern ERCOT has noticeable positive impact on the north-south mode

Frequency (Hz) Damping (%) Frequency (Hz) Damping (%)Morgan Creek-Twin Buttes-Red Creek-Comanche Switch 345 kV Line

0.5800 -0.20 0.5799 0.05

Graham-Jacksboro 345 kV Line 0.5800 -0.20 0.5801 -0.19San Miguel-Pawnee-Coleto Creek 345 kV Line 0.5800 -0.20 0.5702 -1.51Venus-Liggett 345 kV Line 0.5800 -0.20 0.5805 -0.15Anna Switch-Collin-NW Carrollton 345 kV Line Upgrade

0.5800 -0.20 0.5797 -0.17

ConfigurationWithout configuration change With configuration change

Frequency (Hz) Damping (%) Frequency (Hz) Damping (%)Morgan Creek-Twin Buttes-Red Creek-Comanche Switch 345 kV Line

0.6918 9.17 0.6917 9.58

Graham-Jacksboro 345 kV Line 0.6918 9.17 0.6919 9.26San Miguel-Pawnee-Coleto Creek 345 kV Line 0.6918 9.17 0.6900 9.44Venus-Liggett 345 kV Line 0.6918 9.17 0.6914 9.23Anna Switch-Collin-NW Carrollton 345 kV Line Upgrade

0.6918 9.17 0.6916 9.08

ConfigurationWithout configuration change With configuration change

North-south mode

East-west mode

9 April 2002

Impact of the PSS in the AEP Area

Frequency (Hz) Damping (%) Frequency (Hz) Damping (%)

Market Transfer East-west 0.712 5.14 0.7132 15.79High East-West Transfer East-west 0.712 5.59 0.7213 15.36High West-East Transfer North-south 0.564 9.30 0.5751 14.19High West-East Transfer East-west 0.707 3.50 0.7190 29.70High North-South Transfer North-south 0.842 9.39 0.9740 14.60High South-North Transfer North-south 0.600 4.51 0.5970 23.57High South-Rio Grande Valley Transfer East-west 0.721 4.74 0.7317 15.00High Rio Grande Valley-South Transfer East-west 0.708 5.51 0.7185 15.29High From Houston Transfer East-west 0.678 2.37 0.6900 18.77

Scenario(all at 2004 peak load conditions)

Modecompared

Without AEP PSS With AEP PSS

• Addition of 18 PSS in the AEP area significantly improves the damping of the inter-area modes (all results are with tuned PSS and without contingencies)

• In order to maintain a minimum level of damping for the inter-area modes, the following minimum number of PSS must be kelp in service in the AEP area

4 for a 3% minimum damping 7 for a 5% minimum damping

9 April 2002

Details of the north-south mode:

• 2004 Peak Load• High south-north transfer• No contingency was applied for the eigenvalue analysis• Time-domain simulation plot is for the contingency shown

9 April 2002

SSAT Monday, April 08, 2002, 10:09:38

SSAT 1.2critctgscan.binPowertech Labs Inc.

Copyright 2002 All rights reserved

Mapped Mode ShapesReal = 0.0073 1/s Imaginary = 3.6442 rad/s Frequency = 0.5800 Hz Damping = -0.20 %Case: critctgscan.ssa Scenario: 2004 pk southnorth Contingency: No faultDominant State: 8161 : CLO #1 24.0 : 0 : : 1 : GENROU : : Psi_fdMode Shape Reference: 6677 : VALTNTP269.0 : 0 : : 1 : GENROU : : Speed

Unit With Positive Mode ShapeUnit With Negative Mode Shape

Note: Shading Indicates Magnitude.

9 April 2002

SSAT Monday, April 08, 2002, 10:11:43

SSAT 1.2critctgscan.binPowertech Labs Inc.

Copyright 2002 All rights reservedPage 1 of 1

Mode ShapeReal = 0.0073 1/s Imaginary = 3.6442 rad/s Frequency = 0.5800 Hz Damping = -0.20 %Case: critctgscan.ssa Scenario: 2004 pk southnorth Contingency: No faultDominant State: 8161 : CLO #1 24.0 : 0 : : 1 : GENROU : : Psi_fdMode Shape Reference: 6677 : VALTNTP269.0 : 0 : : 1 : GENROU : : Speed

1.00 6677 : VALTNTP269.0 : 0 : : 1 : GENROU : : Speed : 8 [ ]0.96 60000 : ENR_NRP 34.5 : 0 : : 1 : GENROU : : Speed : 8 [ ]0.93 6020 : ENR_SP 34.5 : 0 : : 1 : GENROU : : Speed : 8 [ ]0.91 6637 : KM_NWP 34.5 : 0 : : 1 : GENROU : : Speed : 8 [ ]0.91 60007 : KM_SWP 34.5 : 0 : : 1 : GENROU : : Speed : 8 [ ]0.90 6634 : WDWRDU1 34.5 : 0 : : 1 : GENROU : : Speed : 8 [ ]0.90 60005 : KM_SEP 34.5 : 0 : : 1 : GENROU : : Speed : 8 [ ]0.89 60003 : KM_NEP 34.5 : 0 : : 1 : GENROU : : Speed : 8 [ ]0.87 38332 : WDWRDU2 34.5 : 0 : : 1 : GENROU : : Speed : 8 [ ]0.78 6017 : ORNNWP1 34.5 : 0 : : 1 : GENROU : : Speed : 8 [ ]0.69 6016 : SWMESA 34.5 : 0 : : 1 : GENROU : : Speed : 8 [ ]0.57 1045 : CALENG1G13.8 : 0 : : 1 : GENROU : : Speed : 1 [ ]0.57 1046 : CALENG2G13.8 : 0 : : 2 : GENROU : : Speed : 1 [ ]0.56 11022 : TIECT12G18.0 : 0 : : 1 : GENROU : : Speed : 1 [ ]0.56 11023 : TIECT21G18.0 : 0 : : 1 : GENROU : : Speed : 1 [ ]0.56 11024 : TIECT22G18.0 : 0 : : 1 : GENROU : : Speed : 1 [ ]0.56 11021 : TIECT11G18.0 : 0 : : 1 : GENROU : : Speed : 1 [ ]0.54 1008 : PB6 G18.0 : 0 : : 6 : GENROU : : Speed : 1 [ ]0.50 11020 : TIE ST1G18.0 : 0 : : 1 : GENROU : : Speed : 1 [ ]0.50 11025 : TIE ST2G18.0 : 0 : : 1 : GENROU : : Speed : 1 [ ]

-0.69 8306 : LAP #5 13.8 : 0 : : 5 : GENROU : : Speed : 8 [ ]-0.69 8442 : NBY #7 22.0 : 0 : : 7 : GENROU : : Speed : 8 [ ]-0.69 8459 : DAV #1 24.0 : 0 : : 1 : GENROU : : Speed : 8 [ ]-0.69 8981 : HIDGN1 18.0 : 0 : : 1 : GENROU : : Speed : 8 [ ]-0.69 8982 : HIDGN2 18.0 : 0 : : 2 : GENROU : : Speed : 8 [ ]-0.70 8048 : FAL #1 13.8 : 0 : : 1 : GENSAL : : Speed : 13 [ ]-0.70 8511 : STARCO#113.8 : 0 : : 1 : GENROU : : Speed : 8 [ ]-0.70 8928 : LGEGN#3 13.8 : 0 : : 3 : GENROU : : Speed : 8 [ ]-0.71 8936 : CALGN#1 16.0 : 0 : : 1 : GENROU : : Speed : 8 [ ]-0.71 8937 : CALGN#2 16.0 : 0 : : 2 : GENROU : : Speed : 8 [ ]-0.71 8933 : FGNTS00118.0 : 0 : : 1 : GENROU : : Speed : 8 [ ]-0.71 8934 : FGNTS10118.0 : 0 : : 2 : GENROU : : Speed : 8 [ ]-0.71 8983 : HIDGN3 18.0 : 0 : : 3 : GENROU : : Speed : 8 [ ]-0.73 8517 : CEL-B #113.8 : 0 : : 1 : GENROU : : Speed : 8 [ ]-0.77 8307 : LAP #7 13.8 : 0 : : 7 : GENROU : : Speed : 8 [ ]-0.77 5935 : SI RAY8 13.8 : 0 : : 8 : GENROU : : Speed : 15 [ ]-0.79 8506 : VAL #1 13.8 : 0 : : 1 : GENROU : : Speed : 8 [ ]-0.79 8507 : VAL #2 13.8 : 0 : : 2 : GENROU : : Speed : 8 [ ]-0.81 8457 : COSW#2 13.8 : 0 : : 2 : GENROU : : Speed : 8 [ ]-0.81 8456 : COSW#1 13.8 : 0 : : 1 : GENROU : : Speed : 8 [ ]