Reading through some electrical engineering textbooks written in
the 1930s, the term “frequency” is used to describe what is now
referred to as the “fundamental electric power frequency,” also
known as 60 Hertz (Hz) in North America and some other parts of
the world. In the 1930s, there was only one frequency on the
electrical wires, so it didn’t need extra adjectives to define
it. Load-induced harmonics and interharmonics have since muddied
the waters, and generators are still trying to produce a pure
sine wave at 60Hz. But it doesn’t always look that way to the
loads, and problems can result when it isn’t pure. The sine wave
is a common phenomenon in science that has significance in many
areas. The velocity of a pendulum follows a sine wave, reaching
the maximum velocity at the bottom of the arc and slowing to
zero at the top, before reversing its direction and repeating
the pattern in the other direction. As the magnetic field
rotates around inside the generator, the strength of the field
and the induced e