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Transmitters are regulated utilities that own and operate the high-voltage transmission infrastructure used to transport electricity across Ontario’s bulk power system.
Transmission companies maintain transmission lines, substations, and related equipment that connect large generating facilities with major load centres and distribution systems.
Although transmitters own and maintain the infrastructure, the Independent Electricity System Operator (IESO) controls real-time electricity flows across the network to maintain reliability and operate electricity markets.
Transmission Utility
A regulated utility that owns and operates high-voltage electricity transmission infrastructure used to transport electricity across the bulk power system.
Transmission utilities recover their costs through regulated transmission rates approved by the Ontario Energy Board (OEB). :contentReference[oaicite:1]
⚡ Transmission ownership and system operation are separated in Ontario.
Transmission utilities own and maintain infrastructure, while the IESO manages real-time grid operations and electricity markets.
Several companies are licensed by the Ontario Energy Board to operate electricity transmission infrastructure in Ontario. :contentReference[oaicite:2]
Major transmitters include:
These companies collectively maintain the infrastructure required to transport electricity across the province.
Transmission utilities operate under a regulated cost-recovery framework.
Because transmission infrastructure is considered a natural monopoly, transmission companies do not compete in electricity markets. Instead, they recover their costs through regulated transmission rates.
These regulated rates allow utilities to recover:
Transmission rate applications are reviewed and approved by the Ontario Energy Board. :contentReference[oaicite:5]
Transmission infrastructure must evolve as electricity demand patterns change and new generation resources are developed.
Transmission planning evaluates factors such as:
These planning activities typically involve coordination between:
Although transmission companies own the infrastructure, the IESO controls how electricity flows across the grid in real time.
The IESO monitors:
If transmission constraints occur, the system operator may adjust generator dispatch to maintain reliable system operation.
Related topic:
Independent Electricity System Operator (IESO)
Transmission systems must operate according to strict reliability standards established across North America.
These standards ensure that the electricity system can continue operating safely even if equipment failures occur.
Transmission utilities must maintain infrastructure and operating procedures that comply with these reliability standards.
Consider a situation where electricity demand increases significantly in southern Ontario.
This coordination ensures reliable electricity delivery across the province.
➡ Next Topic: Local Distribution Companies
This topic explains the organizations responsible for delivering electricity to homes and businesses through local distribution networks.
Last Updated: 2026-03-26