Ancillary services
What types of ancillary services does Western provide?
Ancillary services support the transmission of capacity and energy from resources to loads to help maintain a reliable operation. Western offers ancillary services as part of its control area services.
The Federal Energy Regulatory Commission defines ancillary services as:
- Scheduling, System Control and Dispatch —scheduling the amount of energy to be delivered, assigning load and ensuring operational security;
- Reactive Supply and Voltage Control —maintaining correct voltage through adjustments to generator output;
- Regulation and Frequency Response —following the moment-to-moment variations in the demand or supply in the control area;
- Energy Imbalance —providing energy correction for any hourly mismatch between a transmission customer’s energy supply and demand served.
- Spinning Reserves —providing immediate backup service from a reserve unit to serve load in case of a system contingency. (When the reserve unit is operating, it is spinning, thus the name spinning reserve.)
- Supplemental Reserves —serving loads when a contingency exists; not available immediately to serve load but can be available within a short time.
Control areas
Does Western operate any control areas?
Western operates four of 150 control areas within the three power grids in the United States and Canada. Western operates three of 30 control areas within the Western Interconnection. These three control areas are called the WAUM-West, or Western Area Upper Missouri-West, operated by our Upper Great Plains Region; the WALC, or Western Area Lower Colorado, which our Desert Southwest Region operates; and WACM, or Western Area Colorado Missouri, which our Rocky Mountain Region operates. Western's Sierra Nevada Region operates as a contract-based, sub-control area within the Sacramento Municipal Utility District control area.
Western's Upper Great Plains Region also operates a control area in the Eastern Interconnection, or eastern grid, called the Western Area Upper Missouri-East, or the WAUM-East.
How do dispatchers at control areas balance supply and demand?
Dispatchers must match resources (generation) to demand and delivery schedules. They must monitor and maintain system voltage. On an hourly basis, real-time dispatchers validate delivery schedules with each of the other scheduling entities. They also validate these schedules at the end of the day. In addition, they work to verify that delivery schedules for customers are balanced. They manage real-time e-tags—which document the scheduling of energy from an energy supplier and the reservation to transmit that energy—and they assist Automatic Generation Control dispatchers with energy purchases and sales for Area Control Error requirements.
They must also follow procedures and protocols for the regional reliability councils, the North American Electric Reliability Council and Western Electricity Coordinating Council.
How do dispatchers prevent service interruptions?
Supply and demand must be perfectly in balance. Even small imbalances can cause voltage levels to swing significantly. To prevent damage, the grid is designed so that whenever unacceptable fluctuations in voltage levels or frequencies begin to occur at any point in the system (due to lines de-energizing), the generation in the area will immediately shut down. When shutdowns occur at the powerplants, the connections to adjoining areas are designed to automatically isolate the area where the imbalance occurs from the rest of the grid. So power that had been flowing over the line that failed automatically shifts to other, adjacent lines, reducing the risk of interrupting service to end-use customers or overloading lines.
How does Western fit into the North American Electric Reliability Council?
Western is a member of the Western Electricity Coordinating Council and the Mid-Continent Area Power Pool, two of 10 reliability councils of the North American Electric Reliability Council. Western dispatchers also operate Western's system under NERC Operating Criteria. Each system dispatcher must pass a test to become NERC certified. Dispatchers within the Western Interconnection must also be WECC Certified.
Power grid
How does Western fit into the grid?
The United States does not have one national power grid, but rather three separate grids—a Western grid, an Eastern grid and one in Texas, managed by the Electric Reliability Council of Texas. The electric system in the western United States —called the Western Interconnection—operates independently from the electric system in the eastern United States. Western operates primarily in the Western grid and owns and maintains more than 10 percent of the transmission lines in the Western Electricity Coordinating Council area.
Western also operates a control area (Western Area-Upper Missouri East) in the eastern grid, which is called the Eastern Interconnection. Western owns and maintains more than 30 percent of the transmission line mileage in the Mid-Continent Area Power Pool area within the Eastern Interconnection.
How many Direct Current ties are there and does Western operate any?
There are six DC ties connecting the Western Interconnection and the Eastern Interconnection in the United States and one additional DC tie in Canada. Western is associated with four of them. Western owns and operates the Virginia Smith (Sidney, Neb.) DC tie; owns 60 percent of the Miles City DC (Mont.) tie and operates it; and operates the David A. Hamil DC Tie Stegall (Neb.) DC tie (owned by Tri-State Generation and Transmission Cooperative.) Western also operates the back-to-back DC Converter Station project in Rapid City, S.D., owned by Basin Electric Power Cooperative and Black Hills Power and Light. The station can transfer up to 200 MW or power between the Western Electricity Coordinating Council in the Western Interconnection and the Mid-Continent Area Power Pool in the Eastern Interconnection. The other two U.S. ties are Public Service Company of New Mexico 's Blackwater N.M., DC tie and the El Paso Electric and Texas-New Mexico Power Company's Artesia, N.M., DC tie. Xcel Energy is building another DC tie in Lamar, Colo.
Does Western interconnect with other entities?
Western is connected with nearly every utility in the Upper Midwest, Rocky Mountain, and Desert Southwest regions and also has extensive transmission resources in California. Use of this transmission, the transmission available to Western under wheeling contracts with other utilities, and access to the DC ties, allows Western to reach resources and transmit power where needed over most of the western United States. Western also interconnects with merchant generators, such as Calpine’s Sutter powerplant.
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