Hydro-Québec - Learning: Power Transmission

Using the driving force of water, we have set electrons in motion and generated alternating current. But electricity often must travel a very long distance to reach our homes.

Why "transform" electricity?

The transmission of electricity involves a series of transformations, checkpoints and crossroads. These three basic functions are carried out along the way between the power station and the home.

Use the scroll bar below to see electricity's path from the power station to your home.

Power plants like Robert-Bourassa generate electricity at voltages of up to 13,800 volts. But transmission of that electricity occurs at much higher levels, ranging from 44,000 to 765,000 volts. The transmission process begins when step-up transformers in the power station switchyard raise the voltage level. Then, on the way to urban centres, voltages are successively lowered. In the home, we use 120-volt power for the television, radio and other common electrical appliances, or 240-volt power to operate equipment requiring more current, such as the clothes dryer and the stove.


What causes the crackling sound near power lines?



The power system and its interconnections



Put together a power system!


The rise and dominance of alternating current

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Why "transform" electricity?

A transformer is used to raise or lower the voltage of alternating current. Stepping up the voltage facilitates the transmission of massive volumes of electricity, reduces energy losses and lowers the total cost of power transmission—for example, by avoiding the construction of additional power lines. As it approaches the load centres, its voltage is stepped down to the point where homes are supplied with low-voltage power, namely 120/240 volts.

Hydro-Québec’s research institute in Varennes is home to the company’s largest transformer. It weighs 507 tonnes and holds 212,000 litres of mineral oil, an insulating material.

The rise and dominance of alternating current

For transmitting power, alternating current is more effective than direct current. But this was not always the case. Just over 100 years ago, they were rival technologies. Alternating current supporters included George Westinghouse, while Thomas Edison was among those backing direct current. This was the dawning of the age of electricity and American industrialists were seeking the best and cheapest way to bring this new energy from the power station to manufacturing plants. In 1887, Nikola Tesla bolstered the cause for alternating current by developing the first practical system for generating and transmitting alternating current.

What causes the crackling sound near power lines?

Impact acoustique
Hydro-Québec measures the impact of sound produced by its power transmission lines and other equipment.

This phenomenon, called the corona effect, intensifies when impurities fall on the wires and when the air is very humid. The crackling sound is loudest when it snows or rains. Electrons moving between the wires and the air cause the corona effect. This back-and-forth movement creates a multitude of tiny electrical discharges, which we perceive as a crackling sound. The higher the voltage, the greater the chance this phenomenon will occur.