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345 kV High Side Distribution Substation

345 kV High Side Distribution Substation. Jesus A. Guerra, P.E. Distribution System Reliability CenterPoint Energy SWEDE 2011. Agenda. CNP T&D Facts Background of Kuykendahl Substation PTS FailureNew Switching Procedures Addition of Transmission Substation Conclusion Questions.

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345 kV High Side Distribution Substation

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  1. 345 kV High Side Distribution Substation Jesus A. Guerra, P.E. Distribution System Reliability CenterPoint Energy SWEDE 2011

  2. Agenda • CNP T&D Facts • Background of Kuykendahl Substation • PTS Failure\New Switching Procedures • Addition of Transmission Substation • Conclusion • Questions

  3. T&D Facts • CNP T&D serves a 5,000-square-mile area that includes Houston, the nation’s fourth largest city. • CNP delivers electricity on behalf of 79 retail electric providers. • 2+ Million Metered Delivery Customers • 27,726 miles of Overhead Distribution Lines • 3,729 miles of Overhead Transmission Lines • 20,080 miles of Underground Distribution Lines • 26 miles of Underground Transmission Lines • 1521 Distribution circuits • 230 Substations (Transmission and Distribution) • 13 Service Centers

  4. CNP Service Area Map

  5. Background • Kuykendahl (KDL) Substation • CNP’s only 345/35 kV Sub • Built in 2001 • 2-60/80/100 MVA Transformers • Initially serving four circuits • (Currently 5 circuits) • Constructed to serve increased load growth that would result in voltage design criteria violations. • Built on existing CNP property

  6. Location

  7. Substation Site (Cow Pasture)

  8. Substation Site

  9. New Feeder Location

  10. New Feeders

  11. PTS Failures • From 7/31/01 – 10/19/01 three PTS failed during attempts to separate a KDL Feeder from Feeders served by other substations (138/35 kV). • Some failed PTS had successful switching operations. (Crews reported excessive arcing) • Due to unique sub design failures resulted in an open transition switching only until further investigated.

  12. PTS Failures • Identified 3 possible causes for PTS failure: • Excessive currents • PTS Rated for 600A and 900A, breaker setting was lower. • Transient Recovery Voltage (TRV) • Difficult to measure in the field. • TRV model was constructed using ATP (Alternative Transient Program). • (Model showed results were lower than the manufacturer’s TRV ratings) • Switch (Mechanical) Failure • Misalignment, contamination, broken insulators, operator error, etc

  13. PTS Failures • Only the last switch was saved for analysis • Arcing was present. • Manufacturer concluded that interrupters were not properly aligned. • Without the other switches it’s impossible to determine what effect switch failure played in these events.

  14. New Switching Procedure • Load Flow Model simulations revealed large flows of current at the breaker could cause it to trip during routine switching or service restoration. • A new closed transition switching procedure was created. • KDL to KDL switching as 1st option (tie bus at sub) • Other procedures required when rolling the circuit to a particular transformer or adding load to it and performing the operation. • Closed transition would not be possible if one TRF is out of service.

  15. Addition of Transmission Sub • New Transmission Substation • 345/138 kV Sub • Energized 1st Qtr 2010 • Increase capacity for 138 kV lines • 2.5 miles from KDL • Re-evaluation of Switching Procedures

  16. New Transmission Sub

  17. New Transmission Sub 345 Ckt A 345/35 kV Sub 345 Ckt B 138 kV Ckts New 345/138 kV Sub

  18. Re-Evaluation of Switching Procedure • Load Flow study conducted using PSS/E software • L-F studies help determine the steady-state operation on an electrical power system. • 3 models were analyzed to evaluate voltage and current changes at various normally open PTS. • Prior to transmission sub installation • Post installation of transmission sub • Post installation including future load growth

  19. Results • 37 Open PTS studied • Results showed no significant increase in voltage levels prior to and post new transmission sub installation. • Current Changes • 2/3scenarios showed less than 5% change in current levels • 1/3 scenarios showed larger than 5% change: • 8 PTS showed decrease in current up to 33% • 5 PTS showed increase in current (6 – 7%)

  20. Conclusion • The addition of the new transmission sub will allow CNP to continue with the current switching procedures. • As the dynamics of the system changes CNP will have to revisit the switching procedures.

  21. Questions

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