Category: 🧱 Foundations
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Ontario’s electricity system is a large interconnected alternating-current (AC) power system that produces, transmits, and distributes electricity across the province.
The system integrates:
The system is coordinated by the Independent Electricity System Operator (IESO), which operates the provincial grid and administers Ontario’s wholesale electricity market.
Bulk Power System
The bulk power system refers to the large-scale electricity generation and transmission infrastructure that supplies electricity to regional and local distribution systems.
In Ontario, this includes:
⚡ Electricity systems must maintain real-time balance and physical stability simultaneously.
System operators must maintain:
- supply-demand balance
- frequency stability
- voltage stability
- transmission security
These constraints determine how the system operates and how electricity markets are designed.
Ontario’s electricity system operates through the coordination of several major infrastructure and operational layers.
Ontario’s electricity supply comes from a diversified mix of generation resources.
Major categories include:
Each type of generation has different characteristics related to:
Related topic:
Generation Types
Ontario’s transmission system transports electricity over long distances using high-voltage infrastructure.
Typical transmission voltages include:
Transmission infrastructure includes:
The system must operate within thermal, voltage, and stability limits to maintain reliability.
Related topic:
Transmission System
Local distribution companies (LDCs) deliver electricity to residential, commercial, and industrial customers.
Distribution networks operate at lower voltages and include:
Increasingly, distribution systems are integrating distributed energy resources (DERs) such as rooftop solar and battery storage.
Related topic:
Distribution System
The Independent Electricity System Operator (IESO) coordinates real-time system operations.
Core operational responsibilities include:
System operators use sophisticated control systems and real-time monitoring tools to maintain stable operation.
Related topic:
Independent Electricity System Operator (IESO)
Ontario’s grid operates within reliability standards established by the North American Electric Reliability Corporation (NERC).
Reliability standards require the system to withstand a range of contingency events, including:
System operators plan and operate the grid so that the system can withstand the loss of a major component without widespread disruption.
Ontario’s electricity system is interconnected with several neighbouring jurisdictions.
Major interties connect Ontario with:
These interconnections allow electricity to be:
Consider a winter evening when electricity demand rises sharply due to heating loads.
If a major transmission line were to fail, the system would automatically reconfigure to maintain reliability.
➡ Next Topic:
Electricity Value Chain
This topic explains how electricity moves through the electricity sector from generation to consumption and introduces the operational and commercial relationships between market participants.
Last Updated: 2026-03-26