Ancillary Services

Services necessary to support the transmission of electric power.

Definition by FERC

Source: ¹

Those services necessary to support the transmission of electric power from seller to purchaser, given the obligations of control areas and transmitting utilities within those control areas, to maintain reliable operations of the interconnected transmission system. Ancillary services supplied with generation include load following, reactive power-voltage regulation, system protective services, loss compensation service, system control, load dispatch services, and energy imbalance services.

More details can be found in the Reference ² Appendix I: Regional Practices for Ancillary Services.

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Last modified: 2025-06-20

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1. FERC (2020). FERC Glossary - Market Assessments. https://www.ferc.gov/industries-data/market-assessments/overview/glossary ↩

2. NERC (2011). Ancillary Service and Balancing Authority Area Solutions to Integrate Variable Generation. http://web.archive.org/web/20220605060008/https://www.nerc.com/pa/RAPA/ra/Reliability%20Assessments%20DL/IVGTF2-3.pdf ↩