Much of the transmission system was built in the 1950s. As a result, investments are required to replace, repair and upgrade equipment in almost every community to keep the public safe and decrease the number of power outages. Through our three-year, $5 billion investment plan, we will be able to support strong and successful communities.

Why investments in infrastructure need to be made

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1 in 4 transformers have reached their expected service life.

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Nearly 10,000 of our steel towers are over 80 years old.

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1,400 km of our transmission lines are nearly 100 years old.

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Hydro One invests $1.3 billion into the economy by buying goods and services in Ontario each year.

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Construction and maintenance work will support 5,000 highly-skilled jobs in communities across the province.

Hydro One has an important role in the economy.

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A momentary outage can cost manufacturers millions of dollars.

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Attracting businesses to the province depends on a strong transmission system.

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A transmission system failure can leave thousands without power for days.

Investments in infrastructure strengthen local communities.

The transmission system is the backbone of the electricity grid. See how Hydro One is making modest investments in the system to help protect the public, ensure reliability and offset far more costly repair, maintenance and emergency work in the future.


Downtown Toronto

Under streetcar tracks, roadways and subways, runs an underground power line originally installed in the 1950s responsible for powering parts of Canada’s largest city. See how Hydro One is modernizing the aging equipment that so many Toronto businesses, hospitals and schools rely on.


Ottawa Valley

The Ottawa Valley receives their power supply from equipment originally installed by horse and carriage. To build a more reliable system for the region, Hydro One is making critical upgrades that will bolster the local economy for years to come. See how crews will tackle challenging terrain to complete this project.



When a fire broke out at the Minden Transmission Station, it left the community without power for hours. For months, crews worked to repair the station while Minden relied on a fragile system. Find out how this emergency derailed Hydro One’s planned station upgrades.

Some of our major transmission projects:

Map of major transmission projects in Northern Ontario, plus legend

Map of major transmission projects in Southern Ontario

Transmission rates over time have increased
at less than the rate of inflation.


Bar Graph: Transmission rates vs. rate of inflation

* Based on a residential customer with a medium density service type using 750 kWh a month.


Estimated monthly bill increase for a typical household (at 750 kWh per month)
Cost to you in 2020 - 77 cents per month
iCost to you in 2020 - 56 cents per month
Cost to you in 2020 - 59 cents per month

Our role in Ontario's Electricity System

Our transmission and distribution system safely and reliably serves communities throughout Ontario. Transmission rates pay for the cost for Hydro One to operate and maintain the high-voltage system that carries electricity from generating stations to local electric utilities or large industrial customers, such as manufacturers and mines. Our transmission system serves approximately five million customers, directly or indirectly.

Our transmission system is controlled by the Ontario Grid Control Centre and other telecommunications facilities and includes:

Infographic: Electricity System in Ontario Infographic: Electricity System in Ontario

Frequently Asked Questions

What do transmission rates pay for?

Why do you need to increase transmission rates?

What is the proposed increase for Hydro One’s customers?

What charges are included in the Delivery line?

Why does so much of the system need to be replaced?

The electricity system in the province expanded rapidly in the 1950s. Now, those assets are reaching the end of their expected service life and need to be replaced or refurbished.

More Information

For more information about our 2020-22 transmission rate application, please click on the buttons below.