Transcript 6-Workshop-Oncor-onVoltage

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
145
143
139
** 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)
1500
0
1500
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: I2X
MVAr Required to Transmit Power
Over 100 Mi 345 kV Line
Reactive Power(MVAr)
1200
1000
800
600
MVAr
400
200
0
-200
0
100
200
300
400
500
600
700
Loading (MW)
800
900
1000
1100
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.”
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 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.
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