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Old 29th November 2006, 03:53 AM   #1
Nixie is offline Nixie  Canada
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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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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
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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(?).
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Old 29th November 2006, 11:13 AM   #4
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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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