NREL Wind Integration Workshop

1. NREL Wind IntegrationWorkshop By Electric Power Systems, Inc. June 28-29, 2010

2. Wind Integration in the Railbelt • Challenges and Issues • Islanded Electrical System • Power Regulation • Transmission Capacity • Wind Forecasting & Scheduling • Dispatch & Control Responsibility • Control Agreements & Implementation • Voltage Ride-Through Requirements • Frequency Ride-Through Requirements

3. Wind Integration in the Railbelt • Challenges and Issues • Curtailment Procedures & Authority • Fuel Impacts • Hydro-Thermal Inefficiency • Transient Stability, Short Circuit • Transmission Access

4. Islanded Power Systems • Limited Inertia • Displaced hydro/thermal decreases frequency stability • Increased transient frequency excursions • Unit Displacement • Difficult to displace thermal units due to lack of emergency support • Limited Voltage Stability • Displacement of base load units can increase voltage instability • Limited Regulating Units Slide 4

5. Power Regulation • Upward Regulation • Amount of unloaded capacity on other generation units that can be used to make up for decreases in wind power • Downward Regulation • Amount of loaded generation capacity that can be unloaded to allow for increased wind energy • Regulation Expense • Regulation costs vary with unit commitment, time of day and type of unit. Slide 5

6. Power Regulation • Regulation Ramp Rate • The rate at which generation can increase up or down to meet changes in load or wind generation • Regulation ramp rates are generally limited to 4-5% of the unit’s capacity/minute for long-term unit maintenance • Typical ramp rates for thermal units in Railbelt range from1.25 MW/ minute to 3.4 MW/minute • Typical ramp rates for hydros range from 5 MW/minute to 25 MW/minute • Hydros have time constants of 7-15 seconds for upward regulation Slide 6

7. Transmission Capacity • Transmission Constraints • Anchorage – Fairbanks Intertie • Anchorage – Kenai 115 kV line • Transmission today is scheduled energy delivery • Following wind integration, transmission must include regulation capacity • Transmission utilization will decrease with regulation scheduling Slide 7

8. Transmission Capacity • Transmission capacity constraints including regulation will reduce spill energy available from Bradley • Transmission capacity including regulation constraints will decrease energy deliveries from Kenai Slide 8

9. Wind Forecasting & Scheduling • Forecast for daily/weekly wind energy • Interchange scheduling between utilities • Responsibility for forecast deviations • Wind modeling and development costs Slide 9

10. Dispatch & Control • Responsibility for wind monitoring & control area interchange • Alarm and control responsibility • Curtailment control Slide 10

11. Control Agreements • Control agreements required for dynamic scheduling • Hardware/software changes required for dynamic scheduling • Coordination of regulation capacity requirements Slide 11

12. Voltage Ride-Through • VRT is defined for both high and low voltage conditions • Transmission, subtransmission and distribution reclosing coordination requirements • Consistency throughout Railbelt Slide 12

13. Frequency Ride Through • FRT is defined for both high and low frequency conditions • Must coordinate with Railbelt generation • Cumulative wind capacity may represent the largest contingency on the Railbelt • FRT must be consistent throughout Railbelt Slide 13

14. Curtailment Procedures/Authority • Curtailment of wind for generation requirements • Curtailment for transmission • Curtailment for system conditions • Curtailment between control areas • Curtailment by host control area • Unauthorized disconnects • Incident resolution Slide 14

15. Fuel Impacts • Off-schedule wind energy – off-schedule gas requirements • Gas scheduling requirements by plant • Gas penalties applicable to over/under utilization, 3,000 mcf/day • Gas penalties $30/mcf for variance • Gas delivery may not be capable of sustaining generation ramp rates • Penalty allocation will be difficult Slide 15

16. Hydro-Thermal Inefficiency • Hydro currently utilized to: • Mitigate gas constraints • Mitigate transmission constraints • Mitigate thermal generation costs • Hydro “value” is currently optimized to result in least cost generation • Hydro not scheduled during off-peak or shoulder load periods depending on thermal unit commitments Slide 16

17. Hydro-Thermal Inefficiency • Hydro with wind integration: • Provide regulation capacity on hydro & thermal units • Mitigate gas constraints • Mitigate transmission constraints • Mitigate thermal generation costs • Hydro optimized to provide regulation • Hydro scheduled during all load periods with insufficient thermal regulation • Balance of regulating hydro energy vs “ponded” wind energy difficult to forecast Slide 17

18. Transient Stability, Power Flow, Short Circuit Impacts • Standardized procedures and methodologies across Railbelt • Wind models for each important, but difficult to obtain • Without unit de-commitment, not much impact on stability, power flow or short circuit Slide 18

19. Transmission Access • Transmission access costs and methodologies must be developed across Railbelt • WTG facilities on other circuits need system specific transmission rates • Transmission interconnection studies and requirements should be consistent Slide 19