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Update on Flowgate Stability Limit Study Entergy Transmission AFC Stakeholder Meeting Houston, TX September 19, 2006 Problem Definition • The stability limit on the Mt. Olive – Hartburg line defines the maximum MW flow level that can be accommodated on the Mt. Olive – Hartburg line upon the contingency of the Webre – Wells line Study Purpose • To review the existing flowgate limit on the Mt. Olive – Hartburg 500 kV line Perform sensitivity studies to determine if the MW rating of the line could be increased Evaluate solutions/options to improve the flow gate limit Study Assumptions • Peak case 2006 summer peak case Load power factor in WOTAB is 0.945 IPP units in WOTAB are turned on based on the status of firm transmission service Nelson unit 6 or Sabine unit 4 is out of service in the base case • WSCC Criteria applied for voltage dip Voltage Dip Criteria Improve post-fault voltage Minimize motor tripping Study Results Case No. 1 2 3 Case Description 1.With Firm Transaction 2.Nelson U6 off-line 1.With Firm Transaction 2.Nelson U6 off-line 1.With Firm Transaction 2.Nelson U6 off-line Post Contignecy Flow on Mt.Olive – Hartburg 500kV line (MW) Post Contignecy Steady State Voltage at Hartburg 500kV Bus (p.u.) Lowest Bus Voltage Dip & Swing in WOTAB area Max Dip: 0.62p.u. 1260 0.968 Duration of Dip <0.80p.u.: 50 Cycles Max Dip: 0.699p.u. 1150 0.986 Duration of Dip <0.80p.u.: 38 Cycles Max Dip: 0.75p.u. 1045 0.998 Duration of Dip <0.80p.u.: 27 Cycles Sensitivity Study • Peak Case With Nelson Unit 6 on-line at minimum generation (MW) With Sabine unit 4 on-line at minimum generation (MW) • Off-Peak case 2005 Winter Case Load power factor in WOTAB is 0.95 Entergy and IPP units in WOTAB area are dispatched based on historical information Post Contingency Flow on Mt. Olive – Hartburg line is 1250 MW Sensitivity Study Results • Dispatch of Nelson Unit 6 or Sabine Unit 4 has negligible impact on the Mt. Olive – Hartburg 500kV stability limit • Variation in load levels in WOTAB area has very little impact on the Mt. Olive – Hartburg 500kV stability limit Solution Options • SVC Option Peak case 300MVAR SVC at Hartburg 500 & 230kV stations • Series Compensation Option Peak case 50% Series Compensation on Mt. Olive – Hartburg 500kV Line Results of Options Evaluated: • 300MVAR SVC at Hartburg 500 kV and 230kV stations do not yield an improvement in the stability limit • Series compensation has the potential to improve the stability limit Dynamic Simulation Plot Study Summary • Sensitive studies indicate that stability limit on Mt. Olive Hartburg 500kV line is not affected by generation dispatch and load changes in WOTAB area • Series compensation can improve stability limit on Mt. Olive Hartburg 500kV line Entergy will further evaluate this option in their planning process • The flowgate limit will continue to be set to 1050 MW