It's Electrifying! (Split)
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levi
Still fresh, damnit!
I'm not that expert on using different frequencies, but as far as I know current and frequency are independent features of a power supply. Higher frequencies are more commonly used in things these days like USB and HDMI cables, and those are about signal integrity not dumping as much power as you can. I know the invention of twisted pair cables and LVDS (low voltage differential signalling) helped improve signal integrity at higher frequencies, but as I say that's not a high power application and I don't know what pumping dozens of amps down those lines would do apart from blow up the receiving equipment. As far as I know the big power lines running on the pylons you sometimes see from the motorway still run at the national electric frequency (either 50/60Hz). They up the voltage to avoid having to send so many amps down the line, but as far as I know they leave the frequency as is.
Letalis Sonus
Advanced Member
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Some overland lines do use a different frequency, but they use a lower one. Increasing the frequency on a several kilometers long cable with a high amperage would be an EMC nightmare.
I noticed, when i listen to Musik over my Bluetooth Headphones, and i touch the 5V Apple Lightning Plug on my Charging Cable, i hear some Elektrical Interverences ^^
One advantage of DC is that it can easily be supported by batteries. In the days before large power distribution networks, a single factory or a (very) large house might have a private generator, driven by a steam engine.
With AC, there was no way to store the energy, so you had to have a very big generator to meet peak load, and if you wanted power around the clock, you had to pay someone to shovel coal around the clock.
With DC, you could have a smaller generator, run closer to full power during the day, and shut-down at night.
Modern semiconductor inverters allow us to drive the AC grid from batteries, but in 1900, getting AC from DC required moving parts.
As mentioned above, most power distribution is at 50/60Hz, because you simply need a transformer to make it useful to the consumer. However, there are some transmission lines (like the one under the English Channel) which are DC to eliminate reactive power and associated losses. There is a pair of 2GW rectifier-inverters at Calais and Folkstone.
One advantage of high frequencies is that you can get away with smaller transformers. That's the main reason modern consumer PSUs are smaller and lighter than the precursors, and why (I believe) many aeroplanes use 400Hz power distribution.
With AC, there was no way to store the energy, so you had to have a very big generator to meet peak load, and if you wanted power around the clock, you had to pay someone to shovel coal around the clock.
With DC, you could have a smaller generator, run closer to full power during the day, and shut-down at night.
Modern semiconductor inverters allow us to drive the AC grid from batteries, but in 1900, getting AC from DC required moving parts.
As mentioned above, most power distribution is at 50/60Hz, because you simply need a transformer to make it useful to the consumer. However, there are some transmission lines (like the one under the English Channel) which are DC to eliminate reactive power and associated losses. There is a pair of 2GW rectifier-inverters at Calais and Folkstone.
One advantage of high frequencies is that you can get away with smaller transformers. That's the main reason modern consumer PSUs are smaller and lighter than the precursors, and why (I believe) many aeroplanes use 400Hz power distribution.
λ the β-Redex Reducer
β-Redex Reducing Member
Maybe some of you would be interested in "Lessons in Electric Circuits". You should look it up, it's free and legal to download. The first volume is about DC and the second volume is about AC.
levi
Still fresh, damnit!
The main reason modern consumer PSUs are smaller and lighter is that they're no longer linear supplies. Linear supplies directly convert the hundreds of volts AC down to a little above the desired output voltage, which is then rectified and regulated. Switched mode supplies operate internally at much higher voltages, requiring less turns on the input coils of the transformer, so smaller transformer. The act of switching causes high EMF harmonics which have to be suppressed, but the electricity is either 50/60Hz AC or the output DC.
Have you noticed the transformer cores on modern switching PSUs are a lot smaller, as well?
My understanding is that's because the voltage across the 2ndry winding is proportional to not only the number of turns (as you say), but the rate of change of magnetic flux in the core, as produced by a rapid change in current.
If you have a high rate of change of flux, and a low AC frequency - a long period before you turn around and start decreasing it again, it follows that the peak magnetic flux in the core will be large. A given cross-sectional area of iron can only 'carry' so much flux before it saturates. At that point, it performs more like an air-cored transformer - id est, badly!
If you operate a transformer at a very high frequency (as modern PSUs do), you can achieve high rates of change of flux, without saturating even a very thin core.
