Want! Want!

[Sibling Zono (anon1mat0)]

All this discussion brings a question for me, as superconducting lines are coming I had heard somewhere that those work for better DC, is that correct? And what voltages work better with superconducting lines?

[Griffin NoName]

Same here in Aus.  I suspect that one reason for using 240 V is the reduction in Ohmic loss.  For the same power transmission 240 V reduces losses by a factor of 4.

Edison - Tesla
AC
DC
Maybe it's just caused by whoever wins such battles.

EDIT cross posted with Zono's post

[Bob in a quantum-state-of-faith]

All this discussion brings a question for me, as superconducting lines are coming I had heard somewhere that those work for better DC, is that correct? And what voltages work better with superconducting lines?

I do not think superconducting wires "care" one way or another-- what these things have, which is weird, is zero resistance to current-flow (or as near zero as makes no difference).

If you remember Ohm's Law?  It's R= I*V, where I is current (amps) and V is volts and R is resistance.

However.... since we are not permitted to divide by zero.... it complicates things immensely, and you cannot (I would presume) use this to calculate what happens with a superconductor.

One of the weirder things you can do with superconductors?   Is "store" electricity more or less indefinitely.   How?

Easy:  construct a large (really large) electromagnet using superconducting wire-- but, instead of attaching the free ends to a power supply (as you would expect to do), connect them together...  in a continuous loop ....  Next, surround that (or interweave it) with a second set of wires (superconducting or not-- doesn't really matter, but superconducting would be more efficient, and you have to super-cool the other wires anyway...).

These wires' ends, you bring out to your power grid-- this is the load/power supply.  

To store electricity?  You charge up the inner-loop of superconducting wire to a really high gauss (magnetic strength) amount-- say a few million times earth's.   You do this, by sending current into your "charge" circuit-- the ones who's ends you brought out of the superconducting assembly.   So long as the inner loop does not break, the current within it will continue to flow around and around like an endless electronic racetrack-- and the magnetic field will be immense.   Theoretically, you could store an infinite amount here-- but practically, you are limited by your "in and out" wire capacities.   And the overall strength of the whole thing-- too strong a magnetic field would bend things and it'd tear itself to shreds.

To get your charge out?  Apply a load to the wires that come out of the assembly-- and you should get out as much power as you had put in-- in fact, regulating it to come out in a controlled fashion would be your biggest hurdle (as opposed to all at once in a giant lightning bolt..... that would be .. bad.)

All you need to do, to maintain your stored charge, would be to keep everything at super-cold superconducting temperatures....

... it sounds too good to be true, doesn't it?  

As I said-- superconducting is weird.


Edit:  I don't think the volts matter, either-- see Ohm's law... since resistence is zero, in theory, the volts would become infinite, right?  ... right?   

.... it's really, really weird....   

[Roland Deschain]

I remember the R=I*V triangle from school. Superconductivity is really weird, and there is some great research into exotic materials which is looking to get the [metaphorical] holy grail of room temperature superconductors. If the grid was replaced with something like this, it would revolutionise electricity supply, for sure. I remember reading in New Scientist years ago about replacing the grid with cold superconducting materials, and how this was possible to achieve then with enough money pumped into it. Unfortunately, with private commerce running the show in many places, this will not happen any time soon.

[Sibling Zono (anon1mat0)]

I think the argument for DC superconductors was to avoid the inevitable change to it at the end of the line (electric motors can work efficiently on AC but most electric and electronic appliances use DC internally).
--
The superconducting accumulator is a great idea, it reminded me of the flywheel accumulators being developed that had the problem of exotic materials needed to allow them to rotate at very high angular speeds. This would work in an equivalent way but with no moving parts, excellent!

[Bob in a quantum-state-of-faith]

Efficiencies of mechanical conversions from electricity vary a great deal-- depending on a variety of things.

But for simple mechanical rotational power, there are few systems that can beat an AC induction motor.   The speed is directly proportional to two things:  the Hertz (or cycles per second) of the AC itself, and the number of windings in the outer, induction coil(s).   That's it.    There is no need for a speed controller, if a fixed speed (or a limited number of speeds) meets your requirement.

What's more?  The power you can apply to these things is only limited by the capacity of the windings' in the wire-- for a 1/4 horsepower AC induction motor and a 1/2 horsepower motor are exactly the same-- except for the size (diameter/guage) of the internal wiring! 

This is because in an AC induction motor?  It automatically "pulls" as much power as it need to meet the load you place on it's output shaft(s).    It's actually kinda cool that way-- if you have variable load requirements?  You size the motor to meet the highest expected continuous load, and then don't worry about it.  If the load is less than maximum?  No big deal, the motor automatically draws less current.

I love these things-- they were invented/developed over a hundred years ago, and the basic engineering has only changed in the minute details.   And the only moving part, is not electrically charged at all! 

It works like this:  since there is AC power coming into the outer windings (coils)?  This rapidly changing current creates rapidly changing magnetic fields.   Such fields, if you allow soft iron nearby, will induce electrical current-flow, in spite of there not really being a full-circle path-- the frequency is high, so the actual flow is minuscule in length anyway.

But once you have current-flow? You have magnetic fields-- identical to the ones that are inducing the current in the first place. Since the core is free to move?  (it rotates)  It will try to move away from the opposing field, and be attracted towards the opposite field (on the opposite side of a conventional, two-coil design).   In a single-coil design, all you have is the same-type field.  But there are 3 coil, 4 coil, multiple-intertwined coil designs too, but they all work basically the same way).

Now as the inner magnetic field starts to move, the coil's field collapses and reverses-- if this happened at too low a frequency, the inner iron core would simply vibrate back and forth in an oscillation.   But the reversal happens so quickly, and the lag of the core is always behind the actual field, so the same-polarity-opposing fields quickly becomes opposite-attraction fields, pulling the inner core around it's shaft, but before it can get there and "lock", the field reverses yet again.   Round and around it goes.

In classical designs the motor could easily rotate left as well as right-- there was no electromechanical reason to do one or the other-- in fact, on some very early designs, an external handle would start a slow rotation by hand, before you apply power-- and it would continue to rotate at the designed speed on it's one after that.

To overcome this, start-up capacitors were added-- this caused a slight "delay" in part of the windings-- effectively changing a simple winding into a complex one, with part of the winding being partway around the rotational circumference-- this forced the inner core to rotate in one direction only, as when both coils were energized, one was wound one-way, and the capacitor's windings go the opposite way, thus you always begin with matching--same-polarity (push) and opposite-reverse-polarity (pull) magnetic fields with respect to the inner iron core.   A simple reversal of the two wires on the capacitor's coil, and it would rotate in the opposite direction-- handy, if you need bi-directional motors.   (The capacitor acts like a little accumulator-battery in the circuit, storing up, then releasing after a minute delay, the AC current-- this causes the energy to be released slightly behind the main coil's, effectively giving a slightly out-of-phase current to the starting windings.)

To complicate things more?   The inner iron core can be straight-line, essentially parallel to the rotational shaft, or it can be twisted with respect to the shaft, like a very shallow screw's threads, only less than a quarter-turn along it's whole length.   This twist increases the start-up torque, at a minor sacrifice of the running torque.

Then there are multi-phase motors-- each phase acting like an additional cylinder in a radial piston engine, greatly multiplying the delivered power to the shaft.   No starting capacitor needed, no twisted inner core either-- three-phase naturally (due to 3 out-of-phase AC currents) "rotates" the magnetic field around the inner core, depending on how many turns of wire in each winding-- and, obviously, you can have multiple windings for each of the three phases too.


Bottom line is this-- the efficiency of an induction wound AC motor is only limited by the purity of the iron core, and the resistance of it's conductors.   For resistive wire, such as copper, wastes some of the energy as simple heat-- if you got rid of all resistance?

In theory, the induction motor could achieve 100% efficiency.....!   Of course, you'd need a core that was also 100% efficient as well--

....!!

So supercool the whole thing, making everything super-conducting, right?   

In theory, this would be 100% efficient-- and the Universe would explode or something, because you'd violate the 2nd law of thermodynamics....



In the classic design, the inter

[Griffin NoName]

I don't think the volts matter,

They do if you touch an overhead cable.

[Bluenose]

I also suspect that there are safety factors too-- 240v typically is not referenced to ground, with the actual current/loads, whereas 120v typically is-- one "side" of the conductor circuit is referenced to ground (allegedly at a zero float current-- but ground faults do happen, creating a hazardous condition), whereas the other "side" is called "hot" or has potential voltage (120v) with respect to the ground (literal or figuratively, depending on the circumstance).

However, many 240v circuits do have a ground potential, but at 1/2 the voltage (120v), at least here in the USA, they do.

In Aus and the UK, the 240 V is completely different to what you describe.  We run with three phases, each 120 degrees from the next.  The 240 V is measured from the neutral, which is tied to ground at the meterbox at each supply point.  The phase to phase voltage is 415 V.  Supply cabling is via 4 wires, the three phases plus neutral (which is usually thinner than each phase wire, since it only carries difference current between the phases - if all the phase loads were equal it would carry no current).  Each house is supplied from the alternate phases in turn as they run down the street.  Generally homes have only one phase, but occasionally you will get two or even less commonly all three phases into a home.  Larger commercial and industrial sites, of course, usually have a three phase supply. Three phase plugs are much more robust than domestic ones and look completely different (at least in OZ).