ancillary service

Definition

A range of services necessary to the efficient running of the electricity system which are outside the basic needs of energy, generating capacity, and power delivery. Some of these (such as regulation and reactive power) are required during normal operations to maintain the necessary balance between generation and load in real time and maintain voltages within the required ranges. Other ancillary services (such as contingency reserves) provide insurance to prevent minor problems from becoming major catastrophes. Finally, some services (such as system blackstart) are required to restore the bulk-power system to normal operations should a major outage occur. SERN, 2010