NREL Wind Integration Workshop By Electric Power Systems, Inc. June 28-29, 2010

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 Slide 2

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

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

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

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 units 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

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

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

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

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

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

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

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

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

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

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

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

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

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