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Transmission Voltage Management

Learn how varying conditions throughout the day impact system voltage and the strategies utilized to manage voltage adjustments in an electric delivery system. Discover the factors influencing voltage changes and the operational strategies employed to maintain grid stability. Explore the impact of wind speed, power transfers, planned outages, and reactive resource optimization on voltage management.

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Transmission Voltage Management

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  1. Transmission Voltage Management Ross Owen Oncor Electric Delivery

  2. Conditions vary throughout the day that changes system voltage. Some days more than others!

  3. Varying Conditions that Affect Voltage • Daily load curve (2 ½ times) • Generation patterns fluctuate • Power transfers from West Texas • Planned and forced outages • Wind Speed

  4. Voltages Changes during the Day as Station and System Loadings Change 145 143 139 ** There are few days when both high and low adjustments are made within a very short period of time).

  5. West Texas Transfer MW(+ from West) 1500 0 1500

  6. Grid Controllers Schedule Voltage Changes and Make Adjustments 24 x 7 x 365 • Optimize use of available reactive resources: • Add or Remove Capacitors and Reactors • Request Power Plants to Raise/Lower 1-2 kV • Adjust Autotransformer Taps (rare) • Help from neighboring TSPs

  7. Reactor Control Display

  8. Capacitor Control Display

  9. Reactive Reserve Display

  10. Actual Voltage Control mode and Capacitors

  11. Conditions vary between the two extremesLight loads or light transfer levelsHigh system voltagesHigh loads or heavy transfer levelsLow system voltages** Can sometimes happen all of a sudden!

  12. Transmission Line VAR Characteristics • 345 kV lines produce approximately 1.0 MVAR/mile. • 138 kV lines produce approximately 0.1 MVAR/mile. • Reactive line losses consume MVAR: I2X

  13. Spring High Voltage Problems • Scenario was: • Wind generation was minimal. • Planned Outage on long 345 kV Line • in progress. • #1 windfarm at 0 MW/ 40 MVAR output • #2 windfarm at 0 MW/ 17 MVAR output • All area reactors were placed in service • System voltage still 361.4 kV. (Normal Range 340 -359 kV) • When asked to reduce reactive output, windfarms’ response • was “There’s nothing we can do.”

  14. Voltage Operating StrategyVoltage Increasing • Actions as load or transfers decrease: • Decrease Generators voltages as profile allows • Switch reactors in service (after taking 138 kV and substation • capacitors out of service) • Reactive reserve on generator groups should be maintained if possible • Autotransformer LTCs used last if no other choice • (not a reactive source, just shifts MVARs) • Help from neighboring TSPs

  15. Summer Low Voltage Problem • Scenario was: • Wind generation picked up to 3000 MW around 13:00 • System voltage dipped to: • 337 kV Graham SES (Normal Range 340 -359 kV) • 135 kV Breckenridge (Normal Range 139 -143 kV) • Wind farms were asked to raise voltage. Several had to send • personnel. • AEP was asked for assistance. • Reactors removed at Graham and Morgan.

  16. Voltage Operating StrategyVoltage Decreasing • Actions as load or transfers increase: • Switch 138 kV and substation capacitors in service • as load profile allows (after taking reactors out of service) • Increase Generators voltages as profile allows • Reactive reserve on generator groups should be • maintained if possible • Autotransformer LTCs used last if no other choice • (not a reactive source, just shift MVARs) • Help from neighboring TSPs

  17. Take A Ways: All Wind Farms need to be on voltage control mode with monitoring capability Light load / light wind / light transfers = high voltage and Wind Farms should be adsorbing MVARS. High load / high wind / high transfers = low voltage and Wind Farms should be sending out MVARS When there are sudden changes in Wind output we will contact you as soon as possible to adjust voltage set points OPX Extensions are a required by most of our interconnect agreements and need to be answered24 X 7

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