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Contribution of Real Time Transmission Line Ratings to Wind Power

Contribution of Real Time Transmission Line Ratings to Wind Power. ERCOT Regional Planning Group – July 18, 2008. Agenda. Contribution of real time ratings to wind power Brief overview of technology Typical results Everyday, anywhere West Texas wind specific Discussion on market practices

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Contribution of Real Time Transmission Line Ratings to Wind Power

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  1. Contribution of Real Time Transmission Line Ratings to Wind Power ERCOT Regional Planning Group – July 18, 2008

  2. Agenda • Contribution of real time ratings to wind power • Brief overview of technology • Typical results • Everyday, anywhere • West Texas wind specific • Discussion on market practices • Operating • Planning ERCOT Regional Planning Group – July 18, 2008

  3. Contribution Of Real Time Ratings • Increase the capacity of existing interconnections • Avoid curtailments due to transmission constraints • Add turbines to existing wind farms • Faster to market • Add transmission capacity in 60-90 days vs. 1-3 years • Lower development costs • Fraction of the cost of new or upgraded transmission lines ERCOT Regional Planning Group – July 18, 2008

  4. Transmission Line CapabilitiesWhat are real time line ratings? ERCOT Regional Planning Group – July 18, 2008

  5. Transmission Line CapabilitiesWhat Determines Thermal Limits? Example of 20 mi transmission line (795 ACSR) with a steady state thermal rating of 787 amps at 40oC ambient, zero wind, and mid-day in the summer: • Ambient Temperature: • 2oC fluctuation  +/- 2% capacity, • 10oC drop in ambient  + 11% capacity… 874 amps • Solar Radiation: • Cloud shadowing  +/- a few percent, • Total eclipse  + 18% capacity… 929 amps • Wind increase 1 m/sec • 45o angle  + 35% capacity…. 1,060 amps • 90o angle  + 44%capacity ERCOT Regional Planning Group – July 18, 2008

  6. Variability of Wind • Wind along a transmission line has spatial variability. • The spatial variability ranges from centimeters to nearly a kilometer - 200 meters is typical. • One conductor span can be cooled by a 2 m/s wind, while a second span 200 meters away will have no wind. • Wind can not be used to determine the real time thermal rating of the conductor unless many weather stations are placed along the transmission corridor to determine the average temperature of all of the conductor spans. ERCOT Regional Planning Group – July 18, 2008

  7. Variability of Wind • Wind patterns on a bay of Great Lake, Tasmania • Five Minute Intervals • 8:00 a.m. to 8:15 am, 8 March 1998 ERCOT Regional Planning Group – July 18, 2008

  8. Calm Wind Real Time Rating MethodsCapturing the variability of weather • Tension increases in spans cooled by wind, • and decreases in spans not cooled by wind….. Suspension Suspension Suspension Dead-end Dead-end ERCOT Regional Planning Group – July 18, 2008

  9. Real Time Rating Methods Capturing the variability of weather • Suspension insulator strings swing to equalize horizontal conductor tension • Monitoring the conductor’s tension solves the problem of varying winds along the transmission line. • A conductor’s tension is directly related to the average temperature of all the spans in the line section. Suspension Suspension Suspension Dead-end Dead-end Tension Equalizes ERCOT Regional Planning Group – July 18, 2008

  10. Real Time Rating Methods Capturing the variability of weather • Weather and temperature monitors determine the surface temperature of the conductor at only one point • Tension is the result of the average conductor temperature between dead-ends • Tension accounts for varying wind, sun, and ambient • Tension accounts for differences in conductor core and surface temperatures • Tension accounts for variances in conductor manufacturing and installation ERCOT Regional Planning Group – July 18, 2008

  11. Real Time Rating Methods Capturing the variability of weather Tension Based Real Time Rating Systems • Dominant real time rating technology, with 200 real time operational installations in U.S. and abroad. • Equipment installed on transmission structures, to monitor conductor tension and net radiation temperature. • Data is transmitted via radio or optical fibre to the utility’s control center. • Real time ratings are calculated by EMS/SCADA system and displayed to operators. ERCOT Regional Planning Group – July 18, 2008

  12. Real Time Rating Methods Tension Based • Conductor tension is monitored by load cells installed between the dead-end structure and the insulator string. • Load cells are solid stainless steel construction and are specifically designed for the high voltage environment to ensure reliable operation ERCOT Regional Planning Group – July 18, 2008

  13. Real Time Rating MethodsTension Based • Reads conductor tension, net radiation temperature, ambient temperature • Communicates with substation via spread spectrum radio • Solar powered ERCOT Regional Planning Group – July 18, 2008

  14. Real Time Rating SystemsFully integrated with EMS CAT-1™ Remote Monitors Transmission Line License-free Spread Spectrum Radio CATMaster™ Base Station Substation Existing SCADA protocol over substation RTU channel (4-wire Bell 202) IntelliCAT™ for Windows ICCP or file-based data transfer. SCADA/EMS Master Control Center Operator’s Console ERCOT Regional Planning Group – July 18, 2008

  15. Examples of Real Time RatingsEveryday Path or Trunk Capacity ERCOT Regional Planning Group – July 18, 2008

  16. Wind Power138 kV Circuit Capability to a West Texas Wind Farm This line could have been operated at 40 MW higher rating with zero curtailment risk and 62 MW higher rating with 1-2% curtailment risk. ERCOT Regional Planning Group – July 18, 2008

  17. Real Time RatingsEffective Use Present static rating: 540 MVA ERCOT Regional Planning Group – July 18, 2008

  18. Real Time RatingsEffective Use Rating Distribution ERCOT Regional Planning Group – July 18, 2008

  19. Real Time RatingsEffective Use Rating Distribution ERCOT Regional Planning Group – July 18, 2008

  20. Real Time RatingsEffective Use • Most transmission lines are dispatched to survive a first contingency • Assume the static rating is increased to 630 MVA • The risk of a contingency occurring is 0.001 to 0.005. • The risk that the 630 MVA rating will not be available is 0.10 (90th percentile) • The risk of both events occurring at the same time is 0.10 x 0.005 = 0.0005. • 99.95% of the time, the system operates (including first contingency events) without operator intervention. ERCOT Regional Planning Group – July 18, 2008

  21. Real Time RatingsEffective Use Present static rating: 540 MVA ERCOT Regional Planning Group – July 18, 2008

  22. Real Time RatingsEffective Use New static rating: 630 MVA New static rating: 630 MVA ERCOT Regional Planning Group – July 18, 2008

  23. Real Time RatingsEffective Use New static rating: 630 MVA Load ERCOT Regional Planning Group – July 18, 2008

  24. Dynamic Alarms Real Time Rating Static Rating Load Dynamic Alarm Real Time RatingsEffective Use New static rating: 630 MVA ERCOT Regional Planning Group – July 18, 2008

  25. Real Time RatingsShort Term Emergency Rating • Transmission conductors have thermal mass. The conductor takes time to reach its maximum permitted temperature following the application of a step in load current. • The amount of step load can be calculated for any given period of time. ERCOT Regional Planning Group – July 18, 2008

  26. Real Time RatingsDiscussion on planning/operating/market practices • 15 minute ratings • Day ahead ratings • Setting a higher fixed rating • Protecting the T-line when weather is unfavorable • Conditional firm ratings ERCOT Regional Planning Group – July 18, 2008

  27. Real Time Ratings 15 minute ratings • For markets where the transmission line’s rating is updated every 15 minutes, a real time transient rating maximizes the transfer capacity of the line. • Curtailments are minimized. ERCOT Regional Planning Group – July 18, 2008

  28. Real Time RatingsDay ahead ratings West Texas ERCOT Regional Planning Group – July 18, 2008

  29. Real Time RatingsSummary • Flexibility where market can’t be anticipated • Rapid deployment • Maximizes transfer capability of existing lines • Bridge where market can be anticipated • Rapid deployment • Maximizes transfer capability of existing lines • Relocatable – not a stranded asset • Integrates with existing market and operations practice ERCOT Regional Planning Group – July 18, 2008

  30. Real Time RatingsSummary • Applicability • Synergy with wind • Everyday, anywhere • Protects the transmission asset, increases reliability • Provides access to least cost generation • Avoids or minimizes curtailments • Shortens time to market for new generation ERCOT Regional Planning Group – July 18, 2008

  31. Real Time RatingsDiscussion Questions? ERCOT Regional Planning Group – July 18, 2008

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