Increase AC mains frequency?

The line frequency is already optimized, 50 or 60 Hz depending on some tradeoffs.

Synchronous and induction motors would run at 60,000 RPM.

Transformers would scream.

Skin loss would go way up on transmission lines.

Generation would be difficult.

John

The transmission of the signals would probably be lossier, and of course there'd be more radiation of the signal (to cause interference) since the wiring would be more efficient at radiating the signal at higher frequencies.

You don't have to cook up such a scenario to get an answer.

Years ago, and presumably still, aircraft (and I think some ships) used

400Hz AC so the transformers would be smaller.

And any switching supply rectifies the AC line directly, turns it into a comparatively high frequency, so the transformer that actually does the voltage conversion can be smaller.

It would never happen, unles someone was completely starting from scratch in some isolated spot. The changeover, ie the replacement of everything, would be too costly.

Micahel

Primarily higher line losses caused by higher current.

A better idea might be to use DC for distribution, as is already done for high voltage long haul transmission. I think losses are about 1/2 of what they are for 60 Hz AC. Each household could have, essentially, a motor drive type inverter for any AC only electronics. But many appliances are now using small three phase induction motors with their own little V/F inverters, and the first thing they do is convert the AC line to DC. Computers and other similar electronics will happily run on 150 VDC. Such a system would also work well for battery backup.

There are safety issues with DC, but actually 50/60 Hz AC is a dangerous frequency because it causes fibrillation. DC basically makes your muscles contract so you can't let go.

Paul

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Speaking of isolated systems...

I've worked on marine seismic survey gear that uses 2KHz for power distribution along the up to 10km line lengths used. The driver being the smaller transformer sizes required when you have to fit stuff into

70mm diameter cables.

But similar competing systems also use DC for distribution, and I've worked on the specification and design of a 10km+ system that used

600V DC for distribution. Due to voltage drop you could get less than 100V at the tail end of the system, so the DC-DC converter had to be designed for a 70V-600V input span.

Dave.

the

frequencies.

scratch

everything,

What? What the hell kind of a system would drop 83% of it's voltage in the line? That makes zero sense. If the DC line losses are so great then the voltage must be higher to keep the current at a reasonable level.

The best way is a plus and minus DC system then the insulation requirements are about 2.8 times less than that required for an AC system of similar voltage. Voltage handling in the switches and electronics is 1/2 of the actual voltage on the line. Furthermore there are no skin effect considerations or inductive or capacitive loses in the line. Conversion at either end can be at high frequencies, 20kHz or higher keeping the magnetics very small and compact.

Some airplane/submarine systems are supposedly 400 Hz AC, which let's you have smaller transformers at the price of less efficiency (asfaik) and more electromagnetic interference. Also skineffect comes into play and increase losses with higher frequency.

However there might be a more optimal frequency between 60 - 400 Hz. (any suggestion?)

For the last distribution step (less than 1200V) it might be useful with DC distribution due efficient SMPS. And that many appliancies anyway will make DC of the mains as a first step.

Still even if you would start from scratch on an isolated island. The cost to order/special manufacture equipment for an odd mains type can be prohibitive. The only exception being equipment that rectify anyway.

messagenews: snipped-for-privacy@s19g2000prg.googlegroups.com...

It does if you knew the first thing about marine seismic cable systems. In marine seismic systems there is a very delicate balance and trade- off between the gauge of the copper allowed (i.e. it's weight) and the distribution of the hundred or so connected point loads along the system. Everything, including the complex cabling, electronics, connectors (50 pins + fibre) and buoyant flotation material required to keep the entire system floating in the ocean must all be contained within a small diameter in the order of 60mm. DC-DC converter modules are distributed at regular intervals along the cable (which can be up to 10km or more), and these modules can be randomly placed along the cable at any time. So they must be able to handle the highest voltage at the top end, or the lowest voltage at the tail end. And being modular based means you can have several hundred connection points in series with the system, all with their associated worst case tolerances. Total load on the system was many thousands of watts. So add up small diameter copper, hundreds of connections and point loads, and you get some very big losses along the system. It's just the bizarre nature of the business.

That's why the highest possible DC voltage was used. Several factors limited the upper voltage allowed.

We used 64KHz, sychronised with other electronics in the complex (up to 10,000 channel) sampling system.

Dave.

You must be an anus living in a very remote area not to know about the high voltage DC transmission lines in use. The losses are much lower than conventional AC. But then , a person such as you, with very limited education, would not be able to understand the term efficiency.

In a related question, is there any consensus as to whether 120V or

240V mains are better, overall (I can see (some of) the advantages and disadvantages of each, just not the total evaluation)?

You must be a jerk who does not understand the difference between "Transmission" and "Distribution" lines and configurations.

It appears Phil's education is far less limited than yours, though you probably understand an anus far better than us.

sure would. old aircraft (ww II vintage) used to use 400 hz specifically because the equipment was smaller and lighter.

besides AC clocks, huge industrial motors are slaved to the frequency by the 3 phase system; no way to practically change that now.

The higher frequency would make people go crazy. I have worked in an Airforce bunker where you were tortured the whole day with the third harmonics(1200 hz) of the

400 hz mains used there. Frequencies between 200 and 5000 hz are very irritating and leak out of any machine using them. The only cure for these powerfeed frequencies is a wirecutter.

I find that the OFF Switch is easier to find than wire cutters lying around.

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More volt => Less current for the same power => Less copper, Lighter cables, Less magnetic fields, etc..

Donnie: the original post to which we are referring did NOT mention transmission or distribution> It simply asked why not increase the mains frequency. How much more main can you get than transmission lines.