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Author Topic: Why Is AC-Current More Efficient Over Long Distances ?  (Read 4797 times)

Offline guest1289

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Why Is AC-Current More Efficient Over Long Distances ?
« on: January 13, 2017, 09:13:23 PM »
   Why Is AC-Current More Efficient Over Long Distances ?

    I have never found the actual reason,  and the reason is not mentioned on the wikipedia page.

    Is it something like :
      -  dc-current causes more fatigue on the wire/material,  or,  causes it to heat up more than ac-current,  for some reason,   maybe just for the reason that ac-current gives the  conductor-material that short rest before current is sent in the opposite direction(  seems like the most probable answer )
      -  or,  is it possible that in  ac-current  at great distances,  there is some sort of crashing effect between currents going in different directions( in the wire, or in the field around the wire ),  which somehow actually generates surplus current,  or,  boosts current( it would affect the frequency or cause interference ),  the end result being that more  current arrives at the other end. ( they have equipment which cleans the interference of the received current ).   
            So could it be some sort of unofficially known overunity effect of  ac-current  particularly over long distances,   is it possible that it occurs past some sort of specific distance.
   
     It's certainly odd,  because I assume  ac-current  is a very strong emitter of  electromagnetic-radiation( radio signal ) while  steady/smooth  dc-current( from a battery at least ) would emit none,  and yet  ac-current  is more efficient  over long distances.
     
      -  or is it something to do with the electromagnetic-field  around the wire,  but I'm not referring to losses via radio transmission,  even though  initially they seem to be the same thing,   maybe something like friction between the electromagnetic-field and materials outside of the wire,  or something else.

Free Energy | searching for free energy and discussing free energy


Offline lancaIV

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Re: Why Is AC-Current More Efficient Over Long Distances ?
« Reply #1 on: January 13, 2017, 09:34:11 PM »
This is not directly an answer to your question and statements,but since 2 decades there is an alternative for HVAC cables : https://library.e.abb.com/public/3325cb4054a22738c125766400471fd5/HVDC%20Light%20Cables%20for%20long%20distance%20grid%20connection.pdf

http://iopscience.iop.org/article/10.1088/1742-6596/507/3/032037/pdf

one handicap less:
https://www.forumforthefuture.org/greenfutures/articles/breakthrough-long-distance-power-transmission

Often our information stand-point is not up-to-date,or alternatives are not in use cause the common technology and material is only cheaper , this argument only in value because the mass-production from HVAC cables !
And new material can not give us the safety and warranty like the "old"one.

I think the direction for off-shore energy-farming and energy distribution will in future be based by HVDC !


Sincerely
            OCWL


Offline Cherryman

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Re: Why Is AC-Current More Efficient Over Long Distances ?
« Reply #2 on: January 14, 2017, 04:41:42 PM »
I'm no expert.. I always did think it is because DC is pushing electricity along..  the further the more resistance ( as in a water hose)

AC However is not moving the whole distance, it vibrates, by changing the magnetic field at some Hz. the electricity moves enough in its own limited space to excite coils (in appliances)
Thats why AC doesnt handle earth leaks well, at that moment it starts flowing and the system can't handle that.


See it like this..


Take a large rock.. lets say 5 ton , you on one side.. a person on the other  and you want to communicate.
Lets try pushing first (DC )
push te rock for 5 minutes , you have a hard time, and as you move the rock along.. you will either need to supply more rock, or travel yourself. .if you succeed.. then you would be exhausted
Now you take a hammer and give it a whack...   Now the other person will detect sound and/or feel vibration. Thats easy to do with way more less energy.
nothing moved from its place.. and the only thing to replenish is the whack











Offline Magluvin

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Re: Why Is AC-Current More Efficient Over Long Distances ?
« Reply #3 on: January 14, 2017, 05:38:44 PM »
Im going to take a lil stab at it.

Makes me wonder why and how the Edison dc gens putting out 3 to 4kv gets distributed and what level is the voltage at the home or business?

But AC being able to convert very high voltage down to lower high voltages and then finally down to consumer level voltages, allows for very high voltages to be on long distance lines with little loss due to very low amperage where even the use of alum wire with its added resistance compared to copper is virtually nill in added resistance when considering the very high voltage.

DC, especially back then, didnt have the ways we can convert it today. Iimagine the city wire layouts possibly were set in ways that there was equal lengths of wire, aprox, to each destination as to get a safer voltage level after voltage drop through the lines?? 

So AC with the use of transformers allows for very high voltage across long distances, thus very low loss, where as DC, imagine having to deal with that high voltage at the consumer end, if it were 100kv or even 50kv. By the time there is say 400v at the destination, a source of 3 to 4kv with that kind of a voltage drop is big in losses.  I dunno maybe they had high voltage dc motors that ran local gens to lower the dc voltage. Maybe they didnt get to that before AC took over.

Mags


Offline citfta

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Re: Why Is AC-Current More Efficient Over Long Distances ?
« Reply #4 on: January 14, 2017, 06:19:15 PM »
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


Free Energy | searching for free energy and discussing free energy

Re: Why Is AC-Current More Efficient Over Long Distances ?
« Reply #4 on: January 14, 2017, 06:19:15 PM »
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Offline Cherryman

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Re: Why Is AC-Current More Efficient Over Long Distances ?
« Reply #5 on: January 14, 2017, 06:24:31 PM »
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 !


 ;)

Offline Magluvin

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Re: Why Is AC-Current More Efficient Over Long Distances ?
« Reply #6 on: January 14, 2017, 06:27:52 PM »
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


 

Free Energy | searching for free energy and discussing free energy

Re: Why Is AC-Current More Efficient Over Long Distances ?
« Reply #6 on: January 14, 2017, 06:27:52 PM »
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Offline Magluvin

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Re: Why Is AC-Current More Efficient Over Long Distances ?
« Reply #7 on: January 14, 2017, 06:40:11 PM »
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

Offline Magluvin

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Re: Why Is AC-Current More Efficient Over Long Distances ?
« Reply #8 on: January 14, 2017, 06:47:05 PM »
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

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Re: Why Is AC-Current More Efficient Over Long Distances ?
« Reply #9 on: January 14, 2017, 07:22:59 PM »
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.

Free Energy | searching for free energy and discussing free energy

Re: Why Is AC-Current More Efficient Over Long Distances ?
« Reply #9 on: January 14, 2017, 07:22:59 PM »
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Dave45

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Re: Why Is AC-Current More Efficient Over Long Distances ?
« Reply #10 on: January 14, 2017, 07:56:59 PM »
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.

Offline mscoffman

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Re: Why Is AC-Current More Efficient Over Long Distances ?
« Reply #11 on: January 15, 2017, 09:51:42 AM »

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.       


Offline memoryman

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Re: Why Is AC-Current More Efficient Over Long Distances ?
« Reply #12 on: January 15, 2017, 03:23:20 PM »
Nobody mentioned the radiated and skin effect losses with AC power. These favor DC transmission at similar voltages over AC.

Offline verpies

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Re: Why Is AC-Current More Efficient Over Long Distances ?
« Reply #13 on: January 15, 2017, 08:27:22 PM »
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.


Offline Magluvin

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Re: Why Is AC-Current More Efficient Over Long Distances ?
« Reply #14 on: January 16, 2017, 06:39:48 AM »
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
 

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Re: Why Is AC-Current More Efficient Over Long Distances ?
« Reply #14 on: January 16, 2017, 06:39:48 AM »

 

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