The 735-kV transmission system

The 735,000‑volt (735‑kilovolt) transmission system is like a highway that carries huge quantities of electricity over great distances, taking it from where it’s generated to the distribution systems that in turn supply our customers all across the province.

To efficiently transmit electricity over such long distances, the voltage level needs to be high. This both limits the number of power lines required and reduces electrical losses along the way.

The towers that support Hydro‑Québec’s 735‑kV overhead transmission lines, the backbone of its power grid, are robust and imposing.

All of these very high voltage lines are interconnected to form an integrated system. With the addition of new generating facilities to produce clean, renewable electricity, just about all of the lines will have to carry more electricity.

Measuring voltage

Electric current is a little like the water in a garden hose. Voltage, measured in volts (V), is like the water pressure in the hose. Hydro‑Québec’s main grid is at 735,000 volts. North American homes use 120 volts to power most appliances like TVs and radios, and 240 volts for power‑heavy appliances like dryers or stoves.

Did you know?
One 735-kV line is equal to four 315-kV lines, the next voltage level down.

Four-legged tower

This tower is by far the most common on the grid. It’s used for voltage levels ranging from 110,000 to 735,000 volts. It is very versatile and well suited to uneven terrain.

Four-legged tower

Guyed-V tower

This type of tower is used for voltage levels ranging from 230,000 to 735,000 volts. Its advantages include being more economical and generally faster to build than four‑legged towers.

Guyed-V tower

Substations: Essential hubs

As it travels, electricity undergoes a series of transformations and passes through several distribution points. Some substations support the grid, improving both its reliability and its transmission capacity. Others facilitate the energy flow by modulating the voltage before distributing it to other systems, such as those that serve homes or business.

What’s an electrical substation and how does it work?

Explore an electrical substation. See the vital role it plays in transmitting and distributing power from the generating station to the home.

Running time: 4 minutes 41 seconds [in French only]

More documentation on the evolution of the main transmission system: