Why do the americans use a 60Hz system, rather than 50Hz?

[Physicist3]

Hi,

I have been wondering to myself as to the reason for the Americans using a 60Hz power system, rather than the 50Hz that we see as conventional today? The reason for me thinking and wondering this is because I have recently been doing some work with transformers and loss calculations, and obviously in doing this, have seen that hysteresis losses are proportional to the frequency and eddy current losses are proportional to the frequency squared, so obviously this will mean the losses will be higher at 60Hz than 50Hz, basically just costing the Americans more through lost power. If anyone can shed any light on this then I would appreciate it as I can see no real benefit to using 60Hz over 50Hz?

 

[D H]

See this old thread: [thread]53692[/thread].

 

[SteamKing]

The old thread mentioned by DH is a trove of misinformation of the sort that starts, "I heard that ..."

Although it's Wiki, it at least doesn't start, "I heard that ..."

http://en.wikipedia.org/wiki/Utility_frequency

Scroll down to the 'History' section of this article.

 

[Baluncore]

Since so many frequencies were used successfully in the past, the frequency cannot be that functionally critical. The only requirement then is continental standardisation which requires a political rather than a practical decision.

Until we convert to metric time, there will always be 60 minutes in an hour, 60 seconds in a minute and 60 American cycles in a second. There is order in chaos. Seems like a politically rational compromise doesn't it ?

 

[vk6kro]

60 Hz transformers can be smaller than 50 Hz ones for the same power.

This is because the windings can have less inductance for the same reactance.
Reactance = 2*pi* f * L
So the windings can have fewer turns and less iron at the higher frequency.

Properly designed power transformers are very efficient in either system. Efficiencies of 95% or more are normally achieved.

 

[Windadct]

Cause' were not in Europe! -- sorry couldn't resist.

 

[anorlunda]

A Russian study in the 60s (sorry no link) showed that the optimal power frequency would be about 100 Hertz.
Optimality involves many trade-offs, impedance, transformer sizes, and many more factors.

By the way, aircraft systems have long used 440 Hertz as the standard because the weight of the power system (especially transformers) was less. In utility systems, weight counts for very little.

Of course the 100 Hertz optimum is of only slight interest because none of us has the luxury of starting from scratch.

I'll tell an amusing but true story to illustrate that frequency is a question of politics, not engineering.

In the 1970s, the Itaipu Dam was being built on the border between Brazil and Paraguay. The capacity would be 26GW. Paraguay ran at 50 Hertz and Brazil at 60 Hertz. Since Paraguay's load was tiny, almost all of their half of the capacity was to be sold to Brazil. The deal was that the entire 26GW would be 60 Hz, and that Brazil would pay to convert Paraguay to 60 Hz including new appliances for all citizens. My firm designed the transmission system based on that assumption.

But at the last minute, the presidents of Brazil and Paraguay got in a spat. Paraguay declared that their half of the generators would be 50 Hz, conversion of the Paraguayan net was cancelled, but they would still sell the energy to Brazil. Those Paraguayan 13 GW had to be converted electronically from 50 Hz to 60 Hz. The Swedish company ASEA got the $1 Billion contract for the frequency converters, and my firm got to design the transmission system a second time.

Long histories of analogous political decisions determine the frequencies we use today in different parts of the world.

 

[Windadct]

The craziest is the Japanese system - built on one side for Japan by AEG at 50Hz and the other by GE at 60...and while Russian engineering is solid, with a capital S - I would not take a study by them in the 60's on anything to be optimal. The history of the power grid and its design has much more to do with big business and governments than engineering or even economic optimization.

 

[Jon B]

Aircraft ac electrical systems are 400Hz...sorry to nit-pic.