1 Stability Issues in Entergy System Entergy Transmission Planning Summit New Orleans, LA July 10, 2003

2 Classification of Power System Stability Transient/Angle Stability Voltage Stability Small Signal/Oscillatory Stability

3 Limits Corresponding to Voltage Decline Criteria Limits Corresponding to 5 % margin from Nose Point Nose Point ( point before voltage collapse) Static Voltage Stability Criteria

4 Dynamic Voltage Stability Criteria

5 Damping Criteria – 3 %

6 Areas of Stability Concern in 2002 West of the Atchafalaya Basin (WOTAB) North Arkansas Southeast Louisiana Northwest Quadrant III. Stability problem in WOTAB Area II. McKnight-Franklin Flow Limits I. Joint Stability Study between Entergy, Southern, and TVA

7 I. Joint Stability Study between Entergy, Southern, and TVA I. Joint Stability Study between Entergy, Southern, and TVA

8 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.

9 II. McKnight-Franklin Flow Limits II. McKnight-Franklin Flow Limits

10 Problem Area North Arkansas Southeast Louisiana West of the Atchafalaya Basin (WOTAB) Mississippi

11 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

12 III. Stability Problem in Entergy’s WOTAB area III. Stability Problem in Entergy’s WOTAB area

13 Problem Area North Arkansas Southeast Louisiana West of the Atchafalaya Basin (WOTAB) Mississippi

14 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.

15 New Areas of Stability Concern West of the Atchafalaya Basin (WOTAB) North Arkansas Southeast Louisiana V. Western Region Voltage Stability IV. Amite South Stability Mississippi

16 IV. Stability Problem in Entergy’s Amite South Area IV. Stability Problem in Entergy’s Amite South Area

17 Problem Area North Arkansas Southeast Louisiana West of the Atchafalaya Basin (WOTAB) Mississippi Amite South Region

18 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

19 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

20 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

21 System Separation

22 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

23 V. Voltage Stability Problem in Entergy’s Western Region

24 Areas of Stability Concern West of the Atchafalaya Basin (WOTAB) North Arkansas Southeast Louisiana Western Region Mississippi

25 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.

26 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

27 Power – Voltage (P-V) Curve Loss of one Lewis Creek unit and Grimes – Crockett 345 kV line

28 Voltage Profile at Critical Buses

29 Results for 2005 Summer Peak Voltage Instability –Slow voltage recovery –Several motor loads at risk –Depressed voltages can lead to UVLS operation

30 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)

31 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.