Ideal electrical systems (just idle curiosity)

[Andrew Gabriel]

In a typical wire, they move slower than that. However, the wave-front of the movement is typically within one order of magnitude of the speed of light.

[Tim Watts]

That's going to be a big cable to my 3kW kettle and heater ;-)

There's something to be said for higher voltage = lower current and a lower risk of fires.

25mm2 meter cables are bad enough - 125mm2 ??

[Tim Watts]

50% of c for some random coax cable we had to measure the speed of signal propagation in, back in our physics labs.

[Tim Watts]

I thought it was more the issue that you cannot phase lock France and the UK? So DC is a natural choice if you have to re-invert it. And if you have to do that, might as well transmit in DC too.

Not saying your reason is not a good reason - I just thought it was a secondary reason to a fairly immutable primary problem.

[Tim Watts]

Exactly...

[Graham.]

As fast as that? Typical drift speed is less than 1mm/s

[Nightjar]

I think the electricity actually needs to reach the other end of the cable before phase locking becomes a problem :-)

[Johny B Good]

Splutter!!! That's around about 5 or 6 orders of magnitude faster than the typical drift speed of electrons in a copper cable carrying 5 amps in a 1mm diameter conductor (about 0.75 mm squared CSA). Were you, perhaps, thinking of using superconducting cables?

[John Rumm]

Yup, they don't call it "electron drift" for nothing!

[Dave Liquorice]

Even bigger for 10 kW of storage heating... 40 odd amps at 230 V for a few hours makes the tails warm. The 200 A required for a 50 V supply is getting hard to handle.

[The Natural Philosopher]

Actually the ONLY - but overwhelming - advantage of AC is that it can be transformed in terms of voltage by Victorian technology.

The disadvantages are:

- it radiates

- it suffers capacitative current flow that induces extra losses in the resistive cables

- it suffers out of phase losses when ringed over very long distances - continent sized.

- it causes muscle spasms in shock situations.

- it it isn't especially useful in motor situations.

Now that we have reasonably efficient DC to DC converters its is likely it won't be used that much more outside national scale grids..

All medium length underwater and all long length transcontinental inks are now DC

USB style 5V DC power is becoming a de facto standard in low power home situations.

[The Natural Philosopher]

The conductive medium surrounding it means that unlike a 132kV cable string 50 meters in the air, there is considerable capacitance to ground. Only the cable insulation stand between it and ground, and a conductive - a very conductive - ground.

The pout of phase current isn't loss in itself, but it does mean higher currents in the wire for the same power output at the far end and higher currents mean higher resistive losses.

[The Natural Philosopher]

No it really isn't dielectric losses.

[The Natural Philosopher]

WE already are doing this. The cost benefit analysis for DC versus AC is changing as inverter and rectifier costs come down.

That balances with rising costs of electricity and therefore electrical losses in AC circuits.

DC is already preferred for long intergrid links and those spinning offshore white elephants.

Its also the only sane way to connect grids that are not in phase - and that's something IIRC that is an issue over continental grids like the US which is again IIRC more than one grid at different phases.

There is a very good case for domestic DC and in fact that's happening too with USB style sockets being handy for LV electronics.

[The Natural Philosopher]

Well only x5 on what we have now...

[The Natural Philosopher]

Not sure that induction plays any part..

[The Natural Philosopher]

its about power not current

well exactly. its bad enough wiring up three x 50W 12v halogens..

[The Natural Philosopher]

No. I visited the first link to france at the UK end and the issue is primarily one of losses

'we can draw an arc for 30 minutes off the capacitance in that cable'

To drive that capacitance takes a LOT of out of phase current and that suffers resistive losses.

Big ones

[Nightjar]

For a H&S viewpoint, an ELV domestic system would save around 20-25 domestic deaths and around a third of a million serious injuries from electrocution every year.

[Nightjar]

If we were starting entirely from scratch and ELV domestic supplies were considered desirable, would we allow such an inefficient heating system, or would we mandate something more efficient, such as a heat pump? Staring from a clean slate, there might be any number of things that would be done differently from what we have evolved over time.