system voltage planning brian moss pd / transmission planning transmission planning overview october...

System Voltage Planning

Brian MossPD / Transmission Planning

Transmission Planning OverviewOctober 30, 2007

October 30, 2007 System Voltage Planning 2


Nuclear LOCA Voltage Studies (February) Identifies future nuclear switchyard voltage

deficiencies by performing LOCA simulation coupled with contingency analysis on system planning models

Determines minimum nuclear switchyard voltage limits, used to create generator voltage schedules and the TCC’s SCADA/RTCA alarm setpoints for the current year

Annual System Voltage Screening (Spring) Identifies future voltage deficiencies by performing

contingency analysis on system planning models

Annual System Voltage Analysis (Fall) Identifies existing voltage deficiencies by reviewing

the past year’s system voltage performance using PI data



Annual Transmission Capacitor Optimization (Fall) Identifies optimal sites for capacitor placement to

mitigate voltage deficiencies

Annual System Voltage Optimization (Fall) Identifies transmission transformer tap setting and

switched capacitor control setting adjustments to improve system voltage performance

Seasonal System Voltage Optimization Creates “Generator Voltage Schedules” to provide

efficient utilization of system generator voltage support, while maintaining transmission system voltage guidelines and minimum nuclear switchyard voltage limits

Completed and distributed at least 2 weeks prior to start of each season (Spring, Summer, Fall, Winter)


Nuclear LOCA Voltage Studies

Nuclear Generation Inputs (January) Latest minimum grid voltage requirements, as well as

shutdown and LOCA auxiliary loads for each unit

Normal, Pre-LOCA Base Cases Latest summer peak and valley models

Sister Unit Off-Line, Pre-LOCA Base Cases Dispatch variations of normal, pre-LOCA base cases Outage non-LOCA unit at the nuclear station being

evaluated System redispatched to replace outaged unit and

serve its shutdown auxiliary load



Pre-LOCA Contingencies

Pre-LOCA, post-contingency scenario solved to a new steady-state with all equipment (capacitors and transformer taps) allowed to adjust per their control settings

GeneratorLargest Generating Unit on a Voltage

Level at Each Generating Station

Transmission Line44, 100, 230, and 500 kV Lines with

only the Worst-Case Line Outaged for Parallel, Double-Circuit Lines

Transformer100/44, 115/100, 161/66, 230/44,

230/100, 230/100/44, 230/161, and 500/230 kV Transformers

Shunt (Capacitors and Reactors)44, 66, 100, 161, 230, and 500 kV

Capacitors and Reactors



LOCA Event Simulate the initiation of a LOCA event on each pre-

LOCA, post-contingency scenario LOCA unit is outaged and LOCA auxiliary load is applied Energy is imported from off-system to replace outaged

unit and serve its LOCA auxiliary load In order to estimate the switchyard voltage immediately

following the LOCA event, transformer taps and capacitors are prevented from adjusting in the solution due to their long (30+ seconds) response times

Post-LOCA Voltage Evaluation Determine the “LOCA Voltage Drop” (post-LOCA minus

pre-LOCA, post-contingency nuclear switchyard voltage) Post-LOCA voltages are only supported by the pre-LOCA,

post-contingency capacitor MVAr support and the generator MVAR output of all remaining on-line units adjusting to maintain their generator voltage schedules in response to the LOCA event



Pre-Contingency Voltage Limits Equal to minimum grid voltage requirement plus the

worst-case (maximum) “LOCA Voltage Drop” Real-time nuclear switchyard voltage required to

maintain minimum grid voltage requirement in the event of the worst-case, pre-LOCA contingency followed by the initiation of a LOCA event

Generator Voltage Schedule Creation Maintains minimum nuclear switchyard voltage limits

equal to the pre-contingency voltage limits plus 2 kV Additional 2 kV provides an added margin of system

voltage support to the system above the required pre-contingency voltage limits


Generator Voltage Schedules

Pre-Optimization Generator Voltage Schedule (GVS) Cases

Spring(3/21 - 6/20)

Summer(6/21 - 9/20)

Fall(9/21 - 12/20)

Winter(12/21 - 3/20)

Max Load(Mon-Fri)

-100%

Summer Peak(0730-2330)

- -

Peak(Mon-Fri)

76%Summer Peak(0530-2130)



90%Winter Peak(0530-2030)

Off-Peak(Sun-Thur)





Weekend(Fri-Sun)







Pre-Optimization GVS Cases (continued) Latest summer peak, winter peak, or valley models Add transmission projects installed and in-service for

the majority of the season− Capacitors (including portables)− Transformers (including in-service system spares)− Transmission lines (including significant outages)

Generator maintenance outage schedule− Outage generators which are scheduled to be off-line for

maintenance during the majority of the season

Typical dispatch with reduced (75%) generator MVAr capability− Provides a margin of additional MVAr capability not

required to support the provided generator voltage schedules under typical conditions

− Allows generators to follow the provided generator voltage schedules under varying system conditions

Firm, planned transactions



Optimal Power Flow (OPF) Solution Objectives

− Minimize active (MW) and reactive (MVAR) power losses

Constraints− Power balance equation− Transmission system voltage guidelines− Minimum nuclear switchyard voltage limits

Calculated in “Nuclear LOCA Voltage Studies”

− Nuclear generator bus voltage limits Voltages limited by nuclear station auxiliary system design

− Important 100 kV bus voltage limits Significant load service points

− Duke MVAr interface flow constraint Prevent schedules from relying on off-system MVAr import

(0 MVAr net interchange)

− Generator voltage limits− Merchant (IPP) MVAr support requirements



Optimal Power Flow (OPF) Solution (continued) Transformer tap settings are fixed

− Tap settings are optimized in “Annual System Voltage Optimization” and would not be adjusted seasonally

Controls− Generator voltage schedules (MVAr output)− Capacitors (MVAr voltage support)

Generator voltage schedules, Beckerdite SVC voltage setpoint, and reactors’ status are extracted from the optimized cases and provided to the SOC, TCC, and the generation operators as a guide for maintaining optimal system performance under typical seasonal Max Load, Peak, Off-Peak, and Weekend conditions

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