March 12, 2024

The electricity that flows through transmission and distribution systems in Ontario is alternating current (AC).  The current in AC electricity changes direction as part of the rotating machinery generation process, and when graphed, forms a sine wave.  As the generator turns in the downward direction, current flows in one direction, then flows in the opposite direction as the generator continues to turn from the downward to upward direction.  The time required for one revolution of the generator is the Period, as shown on the graph, also known as one cycle.  Frequency is the number of cycles that occur in one second, and is an important aspect of AC electricity.  The unit of measure for frequency is Hertz, named after the German physicist Heinrich Rudolf Hertz (1857–1894) who proved the existence of electromagnetic waves.  Frequency is largely standardized around the world at either 50 or 60 Hertz. The North American standard is 60 Hertz, the European standard is 50 Hertz and the rest of the world is one or the other depending on their history. 

Image of a Sine wave

As with voltage, electricity may need to be adapted in order for electrical equipment designed in one country to function properly in another.  A great example of this occurred when some close acquaintances of mine moved to Jamaica which uses 50 Hertz.  The hands of their clocks, which were designed for the 60 Hertz North American market, only moved 50 minutes every hour.

Initially, there were a variety of frequencies in use around the world.  Early electrical applications tended to be isolated so used a frequency that made the most sense for that particular equipment or generation.  Frequencies in use ranged from 25 – 140 Hertz.  As local grids developed, it became necessary for the frequencies to be standardized as there could only be one frequency on a grid.  As these local grids became interconnected further standardization was required.  After World War II most countries moved to a national standard though this often took decades to implement.  As per above, most countries with a strong European influence moved to 50 Hertz while those with a stronger American influence moved to 60 Hertz.

The standardization at 50 or 60 Hertz represented a compromise.  Some industrial equipment operates best at lower frequencies, some household equipment (lighting) is better at higher frequencies and some industrial machinery is best at very high frequencies.   When incandescent lamps, for example, were connected to 25 Hertz power supplies, the lights flickered; not so with 50 or more hertz.  Where needed, businesses can still transform the frequency and voltage of their power after receiving it from their local distributor. 

In some cases, local grids remained at the old frequencies.  A great example of this was here in Niagara where some refineries continued using 25 Hertz power into the 2000’s.  What is now the Niagara Power Station of the Niagara Parks Commission was one of the providers of the 25 Hertz power.  However, even these customers had to move to 60 Hertz power as the suppliers of 25 hertz power were gradually closed.

Electrical equipment approved for use in North America is designed for 60 Hertz power.  However, much electronic equipment is not.  It is designed for direct current (DC) rather than AC power.  DC power has no frequency as that current does not change direction.  The boxes on the power cords used to plug in this electronic equipment converts the power from AC to DC through the rectification process.  Conversely, when required, DC is converted to AC through an inverter.  The adapters used for personal travel raise or lower the AC voltage AND frequency to the appropriate levels.

1 thought on “Frequency

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