Transmission Voltage Management Ross Owen Oncor Electric Delivery

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

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

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

West Texas Transfer MW (+ from West)

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

Reactor Control Display

Capacitor Control Display

Reactive Reserve Display

Actual Voltage Control mode and Capacitors

Conditions vary between the two extremes Light loads or light transfer levels High system voltages High loads or heavy transfer levels Low system voltages ** Can sometimes happen all of a sudden!

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: I 2 X

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 kV. (Normal Range kV) When asked to reduce reactive output, windfarms’ response was “There’s nothing we can do.”

Voltage Operating Strategy Voltage 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

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 kV) 135 kV Breckenridge (Normal Range kV) Wind farms were asked to raise voltage. Several had to send personnel. AEP was asked for assistance. Reactors removed at Graham and Morgan.

Voltage Operating Strategy Voltage 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

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 answered 24 X 7