Why Is AC-Current More Efficient Over Long Distances ?

[Cherryman]

Why is it so hard for people to just do a simple search for their answers?  Here is a fairly in depth article and discussion about the pros and cons of using AC for long distance power transfer.

https://www.quora.com/Why-is-alternating-current-better-for-long-distance-power-transmission-than-direct-current

That's no fun!


Sometimes you have to think a little for yourself first !

[Magluvin]

Like using a power saw with a long extension cord, you can feel the power drop vs plugging the power saw in the outlet directly. So AC at very high voltages, which can be simply converted, is where we get better efficiency.

Like if we were to have DC at the source station, say 3kv, then we wanted to run that power saw at the power outlet in the distance, the saw most likely runs at some lower voltage, requiring more current for a given wood cutting power level. So the source at a distance has to provide all this current to run the saw that is running on a lower input voltage than the source. So the saw is a low impedance or in dc terms, low resistance load. Where as the hv ac from the source is met with very high resistance primaries of the step down transformer at the destination. So that helps in reducing the high tension line voltage drops by not applying heavy current loads.

So DC is an issue compared to hv ac for distant power transfer. Most likely the best bet is to use dc for storage and use efficient inverters to distribute power when it comes to power storage on the electric grid, which is what I believe they do now. Read an article about using used lipo batteries from electric cars as sub station storage in some cases.

Mags

[Magluvin]

I remember SoundStream car amps in the early days, the dc to dc power supply inverter was a separate module. The inverter module was mounted close to the battery and the AC out was sent back to the amp where it was rectified and cap storage for rail voltages. Might seem silly. But when you are raising the voltage in the amplifier to higher rail voltages than the 12v dc input, then the heavy gauge power wire requirement becomes less. So a twisted pair of 14awg to run the inverter output to the amp is probably as good as running a 4awg 12 back to the trunk, mostly because the inverter output was 35v to 45v, depending on the amps of the time that used this system. So to get the same power back to the amplifier circuits, the current through the twisted pair power wires carried less than half the current requirement of 12v over the distance from the battery to the trunk.


Mags

[Magluvin]

And most likely having DC at very high voltages such as we can with ac would be probably lossy just due to having a constant very high voltage charge out in the open. Like lightning always ready to strike.

Mags

[Dave45]

Not sure if the technology was available in Edison's time but a boost converter will raise the dc to considerable voltages for the transfer then it can be stepped down using the buck converter.
But even short distances (10 feet) require large wire using say 12v dc, but would that be the case using say 120 volts dc, probably not.
Using AC was inevitable because of the north an south of permanent magnets and their use in generating power.