DEC System Voltage Planning - June 2018 Brian Moss, P.E., Lead Engineer, Transmission Planning Carolinas

DEC System Voltage Planning 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

DEC System Voltage Planning Annual Transmission Capacitor Optimization (Spring or 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 (Spring, Summer, Fall, Winter) 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 issued to Generators at least 30 days prior to implementation date around the start of each season

DEC Nuclear LOCA 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

DEC Nuclear LOCA Studies 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 Generator Largest Generating Unit on a Voltage Level at Each Generating Station Transmission Line 44, 100, 230, and 500 kV Lines with only the Worst-Case Line Outaged for Parallel, Double-Circuit Lines Transformer 100/44, 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

DEC Nuclear LOCA Studies 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

DEC Nuclear LOCA Studies 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

DEC Generator Voltage Schedules and Reactive Support Generator Voltage Schedules (GVSs) in DEC Largest Generators, Solar PV, and SVC Switchyard Voltage Generator Bus Voltage Reactive Operating Schedule Seasonal Schedules Spring, Summer, Fall, Winter Weekday Peak Weekday Off-Peak Weekend All Hours Plant operators are expected to follow schedules 24/7 unless directed by the System Operating Center (SOC)

DEC Generator Voltage Schedules and Reactive Support Schedule Creation in DEC System voltage optimization using PSSE Optimal Power Flow (OPF) Reduced (75%) Generator MVAR capability Minimize system losses Transmission System Voltage Guidelines Nuclear LOCA switchyard and generator bus voltage requirements Net Duke MVAR Interchange held at 0 to not rely on off-system MVAR support Merchant (IPP) MVAR support requirements Pre-Optimization Generator Voltage Schedule (GVS) Cases

DEC Generator Voltage Schedules and Reactive Support 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

DEC Generator Voltage Schedules and Reactive Support 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 Nuclear generator bus voltage limits Important 100 kV bus voltage limits 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

DEC Generator Voltage Schedules and Reactive Support 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 Peak, Off-Peak, and Weekend conditions

DEC Generator Voltage Schedules and Reactive Support

DEC Generator Voltage Schedules and Reactive Support

DEC Generator Voltage Schedules and Reactive Support

DEC Generator Voltage Schedules and Reactive Support If system conditions prevent MVA limited units from operating within the GVS upper and lower bounds, the unit may need to reduce MW output to GCC (or below as directed by the SOC) to comply with PF bound requirements. All units may operate above GCC as long as system conditions allow them to operate within GVS upper and lower bounds.

DEC Generator Reactive Support Requirements New Generator Voltage Support - Facility Connection Requirements (FCR)

DEC Reactive Capability Study Identify the GSU tap setting that maximizes MVAR output capability to support the transmission system across wide ranges of switchyard and generator bus voltages Used to optimize GSU Tap Settings to improve ability to support GVSs Used in FS and SIS to determine if Generator can provide sufficient VAR support to the Transmission System

DEC Reactive Capability Study