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In addition to producing electricity, the power system requires several supporting services to operate safely and reliably. These services are known as ancillary services.
Ancillary services help maintain the stability of the electricity grid by supporting essential system functions such as balancing supply and demand, maintaining system frequency, and ensuring that backup electricity is available if needed.
In Ontario, ancillary services are coordinated by the Independent Electricity System Operator (IESO).
⚡ Ancillary services help keep the electricity system stable.
They provide additional support that allows the power system to respond quickly to changes in supply, demand, or unexpected events.
Ancillary Services
Ancillary services are services that support the reliable operation of the electricity system but do not directly produce electricity for consumption.
Electricity systems must respond quickly to changing conditions.
For example:
Ancillary services provide the flexibility needed to respond to these situations and maintain system stability.
Several types of ancillary services are commonly used to support electricity system reliability.
Operating reserve is backup generation capacity that can quickly supply electricity if needed.
These reserves help ensure that the system can continue operating if a generator unexpectedly stops producing electricity.
Regulation services help maintain the frequency of the electricity system.
Small changes in supply and demand occur continuously, and regulation resources help correct these imbalances.
Voltage support services help maintain stable voltage levels across the transmission system.
Stable voltage is necessary for electricity equipment and infrastructure to operate properly.
The Independent Electricity System Operator (IESO) manages ancillary services as part of its responsibility for maintaining grid reliability.
The IESO ensures that enough ancillary services are available to support the electricity system under normal and emergency conditions.
Related topic:
Independent Electricity System Operator (IESO)
Consider a situation where a large power plant unexpectedly shuts down.
Ancillary services allow the system to respond quickly and prevent disruptions to electricity supply.
➡ Next Topic:
Electricity Settlements
This topic explains how financial transactions are calculated and settled between participants in Ontario’s electricity market.
Last Updated: 2026-03-26