1

Stability Issues in Entergy Stability Issues in Entergy

System System

Entergy Transmission Planning Summit Entergy Transmission Planning Summit

New Orleans, LA New Orleans, LA

July 10, 2003July 10, 2003

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Classification of Power System Stability

• Transient/Angle Stability

• Voltage Stability

• Small Signal/Oscillatory Stability

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190

240

290

340

390

440

490

540

590

640

LOAD ------->

0.648

0.668

0.688

0.708

0.728

0.748

0.768

0.788

0.808

0.828

0.848

0.868

0.888

0.908

0.928

0.948

0.968

0.988

p.u

. V

oltage

Limits Corresponding to Voltage Decline Criteria

Limits Corresponding to 5 % margin from Nose Point

Nose Point ( point before voltage collapse)

Static Voltage Stability Criteria

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Dynamic Voltage Stability Criteria

5TSATPowertech Labs Inc.

Nanjing Automation Research Institute

Copyright © 2002 All rights reserved

Thursday, March 14, 2002, 13:39:57

Generator angle (degrees)

Time in seconds

0.000 4.000 8.000 12.000 16.000 20.000-120

-54

12

78

144

210

Damping Criteria – 3 %

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Areas of Stability Concern in 2002

West of the Atchafalaya Basin(WOTAB)

North Arkansas

Southeast Louisiana

Northwest Quadrant

III. Stability problem in WOTAB AreaII. McKnight-Franklin Flow Limits

I. Joint Stability Study between

Entergy, Southern, and TVA

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I. Joint Stability Study I. Joint Stability Study

between Entergy, Southern, between Entergy, Southern,

and TVA and TVA

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Results/Northwest Quadrant

• New generation added without PSS severely deteriorated system damping.

• The most limiting contingency from a damping standpoint was the Miller - Bellefonte 500 kV line.

• The most limiting contingency from a voltage standpoint was the Farley - Mitchell 500 kV line.

• With PSS on new generating units, the export limits were found to be 3,850 MW.

• Current Status: Problem doesn’t exist any more due to cancellation of some IPP generation.

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II. McKnight-Franklin Flow II. McKnight-Franklin Flow

Limits Limits

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Problem Area

North Arkansas

Southeast Louisiana

West of the Atchafalaya Basin(WOTAB)

Mississippi

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Results/Southeast Louisiana

• Angle Stability limits found to be slightly lower than voltage stability limits

• Rating of the McKnight-Franklin 500kV line limited to 2,070 MVA due to unacceptable damping– With Webre-Richard out of service, the flow limit is 1,958 MVA– With Daniel-McKnight out of service, the flow limit is 1,522 MVA

• No transient voltage security violations observed

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III. Stability Problem in III. Stability Problem in

Entergy’s WOTAB area Entergy’s WOTAB area

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Problem Area

North Arkansas

Southeast Louisiana

West of the Atchafalaya Basin(WOTAB)

Mississippi

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Results/WOTAB

• The limiting contingency is the Mt. Olive - Hartburg 500 kV line.

• Without PSS, the limit is 2,700 MW based on damping criteria ( < 3% damping).

• With PSS on new generating units, the export limit was found to be 3300 MW based on voltage collapse criteria.

• Limit based on voltage decline criteria (0.92 pu) is 2,100 MW.

• Major transmission improvements may be required to increase export limits.

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New Areas of Stability Concern

West of the Atchafalaya Basin(WOTAB)

North Arkansas

Southeast LouisianaV. Western Region Voltage Stability

IV. Amite South Stability

Mississippi

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IV. Stability Problem in IV. Stability Problem in

Entergy’s Amite South Area Entergy’s Amite South Area

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Problem Area

North Arkansas

Southeast Louisiana

West of the Atchafalaya Basin(WOTAB)

Mississippi

Amite South Region

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Background

• Major Load Center

• Large Concentration of Generation

• Expected 2003 conditions:– 6,280 MW of load (including CLECO & LaGEN

loads)– 8,400 MW of native and new generation

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Background

• 230 kV loop out of Waterford is critical– Approximately 3,100 MW generation in the loop– System stable for primary clearing faults– Additional generation can lead to instability for

stuck breaker faults

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Results

• Under stuck breaker faults– Fault clearing time very important for the stability

of the region– Units in Amite south region and close vicinity can

separate from the rest of the system– Can lead to lines tripping

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System Separation

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Solutions Proposed

• Faster fault clearing devices (relays, breakers)

• Remedial action scheme to trip certain units to protect against stuck breaker fault conditions

• Power system stabilizers on the new units

• IPO breakers

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V. Voltage Stability Problem V. Voltage Stability Problem

in Entergy’s Western Region in Entergy’s Western Region

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Areas of Stability Concern

West of the Atchafalaya Basin(WOTAB)

North Arkansas

Southeast LouisianaWestern Region

Mississippi

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Background

• Western Region load growth: ~ 5.1 %

• Generation sources: Two Lewis Creek units (226MW & 230MW, 150 MVAR each)

• With one Lewis Creek unit out of service, certain line outages can cause low voltages leading to potential voltage collapse.

• Critical tie lines are Grimes – Crockett 345 kV and China – Jacinto 230 kV.

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Background

• Currently, Under Voltage Load Shedding (UVLS) scheme is in place.– Voltage at critical buses below 0.92 pu

– Loss of both Lewis Creek generators

– Lewis Creek units go into over excitation mode

• Series Compensation on China – Jacinto 230 kV line• Static capacitors installed – 770 MVAR• Two D-SMES units (8 MVA each) installed at New

Caney and Metro in 2001

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0.92

0.94

0.96

0.98

1

1.02

1.04

1300.00 1350.00 1400.00 1450.00 1500.00 1550.00 1600.00

Western Region Load Level (MW)

Vo

ltag

e (P

.U.)

Metro138

Conroe138

Lewis138

Tamina138

Goslin138

Jacinto138

Jacinto230

NAVSOTA138

Grimes138

CALVERT69

NewCaney138

Rivtrin138

Dayton138

Cypress138

Power – Voltage (P-V) CurveLoss of one Lewis Creek unit and Grimes – Crockett 345 kV

line

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Voltage Profile at Critical Buses

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Results for 2005 Summer Peak

• Voltage Instability– Slow voltage recovery – Several motor loads at risk – Depressed voltages can lead to UVLS operation

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Possible Solutions

• Static Devices – MS Shunt Cap Banks

• Series Compensation

• New transmission facilities (for details, see EGSI-TX’s area planning presentation)

• Dynamic VAR support device (e.g., SVC, STATCOM, D-SMES)

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System Stability Summary

• PSS installation mandatory for all new generation locating on the Entergy system

• PSS tuning mandatory in WOTAB and Southeast Louisiana

• Traditional methods are needed to fix stability problems (alleviate thermal constraints, additional static reactive power support devices, series compensation)

• New technologies (FACTS devices, e.g., SVC, STATCOM, D-SMES, UPFC, etc.) may be required.