Why Is AC-Current More Efficient Over Long Distances ?

[Dave45]

Contrary to popular belief Tesla did not invent AC or the transformer, he did invent the AC motor an perfected the use of AC as we know it today.

[mscoffman]

Your actual initial statement is completely incorrect. At first Edison Dynamo's were DC generators. Most utility generator even today are set up
to give about 1050Volts output. People then wanted to go with AC because Transformer technology allowed an inexpensive way to easily adjust
voltage levels, even to the extremes like 10E^8 Volts. P=E*I  Power stays relatively the same after transformation. but the resistor equation E=I^2/R
says that for the inevitable resistance of the line R. The power loss goes up linearly with voltage but goes up with the square power of current. This
means to minimize losses you want to decrease the current absolutely and much as possible and increase the voltage as much as possible. This is why
most of the power grid works with variable wire sizes and transformer substations and individual transformers in the field to defeat the resistance of line
attenuating then to transform electricity to nearly match the standards customers need. fast forward 70 years and the new technology is now semiconductors
rather than transformers.  It turns out that using semiconductor one can create whatever AC frequency one wants even at the extraordinary levels of utility
electrical power. Now it becomes better to transmit DC at 500million volts and AC HV has some capacitive losses even at low 50/60Hz. This ultrahigh DC HV
at ultrahigh power is transmitted over something called Interstate Intertie lines which in the US run generally north and south because it is not yet economic
to transmit power from east west. There is a huge new site in New Mexico, I think ,that will be the next step. Superconductor DC power transmission lines will
allow the Western US excesses of wind power and solar power to be distributed to loads on the East and West coasts.       

[memoryman]

Nobody mentioned the radiated and skin effect losses with AC power. These favor DC transmission at similar voltages over AC.

[verpies]

Why is AC-Current More Efficient Over Long Distances ?

AC isn't more efficient to transfer than DC.  DC is.

AC suffers inductive and capacitive losses as well as skin-effect and proximity-effect.
AC is easier to transform up and down, though, but that has nothing to do with distance.

[Magluvin]

AC isn't more efficient to transfer than DC.  DC is.

AC suffers inductive and capacitive losses as well as skin-effect and proximity-effect.
AC is easier to transform up and down, though, but that has nothing to do with distance.

Well that was what I was getting at saying the extension cord inline with a power saw will show a very noticeable drop in saw power as compared to the saw connected direct to the outlet. Now if the outlet voltage was higher and the saw is able to run at that higher voltage, adding the cord again would show less of a drop at the saw. So the use of higher voltage does overcome resistance losses.

Like a home built EV. One may be running at 72v at 600A controller, there is a potential of 43kw. That would be 6 12v batts in series.
But if you are really into it, and you use 25 batteries, then you will have 300v. You will only have to pull 144A to get the same 43kw at the controller. So now, the big power wires, the same used in the 72v EV, will dissipate less resistance losses at 144A than at 600A.  So the higher the voltage the system is, the more efficient the power levels.

AC is just so much easier, even these days with switching power supplies, to use as it is. The simple transformers take the place of switching power supplies, of which would be much more expensive to build considering the high voltage levels, total and peak power requirements at power plant and substation levels. Again, unless the step ups and step downs were dc motors driving gens could DC be used in the same manner.

Was looking at a switch the other day. The higher the voltage, the lower the amps. So its not the amps really that limit the rating of the switch, its the wattage.   Fuses are rated at a particular amperage and at a particular voltage. If we have a 120v 20A fuse, and it will blow at 20A, will the same fuse blow at 20A if the circuit were only 12v? Or will the fuse carry more current at 12v line?  So now lets use the same fuse at 220v. Will it take 20A to blow the fuse this time, or will it blow at less than 20A?

Mags