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Why is mains frequency so low?
Why is mains frequency so low?
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Old 29th November 2006, 03:53 AM   #1
Nixie is offline Nixie  Canada
Join Date: Jan 2006
Location: Vancouver, BC
Question Why is mains frequency so low?

Why was 50/60 Hz chosen? With higher frequencies, smaller transformers could be used.
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Old 29th November 2006, 06:31 AM   #2
dnsey is offline dnsey  United Kingdom
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Location: Shropshire, England
It's a function of the generator design, as is the sine waveform.
In theory, you could have more poles, so as to produce a higher frequency, but there wouldn't be enough space to wind the wire (which is in reality heavy bar at these currents).

A further reason: when switching between generators, phase used to be adjusted manually (by observation on a dual-beam scope and adjusting generator speed). It's now done by computer, but used to be a skilled job even at LF. Imagine trying it at a higher frequency!
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Old 29th November 2006, 07:01 AM   #3
peranders is offline peranders  Sweden
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Why is mains frequency so low?
It has also to do with distribution losses I'll guess. In Sweden (1800 km) you will get problems with wave lenghts if the frequency is higher. If you have a two pole motor you'll get 3000 or 3600 rpm which is good and not too fast.

The trains in Sweden has 15 Hz which later became 1/3 of 50 Hz (= 16.67Hz) and this was because we could make better transformers in 1925(?).
/Per-Anders (my first name) or P-A as my friends call me
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Old 29th November 2006, 11:13 AM   #4
ralphs99 is offline ralphs99  Australia
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Hi Nixie,

An important consideration is the skin effect. AC currents tend to flow at the surface of a conductor rather than through the middle.

In copper at 60Hz the skin effect depth is only 8mm, so solid wires more than twice this thick are a waste of conductive material.

As frequency increases, the depth decreases making transmission line design more difficult.

Cheers, Ralph
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