Ancillary services are services that make the transmission system “work.” They support transmission of capacity and energy from resources to loads while maintaining reliable system operation.

Ancillary services include:

  • scheduling, system control and dispatch service – schedules the amount of energy to be delivered, assigning load and ensuring operational security, among other tasks;
  • reactive supply and voltage control from generation sources service – maintains correct voltage through adjustment to generator output;
  • energy imbalance service – provides energy correction for any hourly mismatch between a transmission customer’s energy supply and demand served;
  • regulation and frequency response service – follows the moment-to-moment variations in the demand or supply in the control area;
  • operating spinning reserve service – provides immediate back-up service from a reserve unit to serve load in case of a system contingency;
  • operating supplemental reserve service – serves load when a contingency exists; not available immediately to serve load but can be available within a short time.

We develop transmission agreements for these services and may modify them upon written notice to the customer. In some projects, customers can get credit on their own power bills if they receive the service from another source or supply it from their own load. If the resources are not available to provide these services, WAPA will offer to purchase the service and pass through the costs to the customer, plus administrative fees.


Last modified on September 7th, 2023