DC mains (was: Are 3A plug fuses really necessary?)

[harry]

Virtually all long distance transmission is DC these days.

[harry]

In days of yore it was the only way. There are other ways now. As renewable electricity supplies come in,long distance DC power transmission will be needed increasingly.

[Capitol]

HVDC power transmission has been the norm since before 1950.

[Scott]

Thanks, but are you sure you were supposed to use your foot? Was this not a lazy alternative to leaning down and operating the switch manually?

[Andrew Gabriel]

Many appliances would run on both. Fluorescent lights were an exception where, although the DC fittings could also run on AC, AC fittings couldn't use DC.

I think a more significant change in terms of users impacted was the conversion to 240V from a variety of other voltages (200V in Reading where my parents were at the time). The Electricity Board came and did a survey of all electrical appliances (which was considerably fewer than a household would have today), and arranged to have appliances adapted or replaced at their expense. Things like fluorescent lamps had voltage tappings on ballasts anyway due to voltage variation across areas. My parents' washing machine had a sodding great autotransformer fitted inside it (I kept it for a while after the machine was scrapped), and they fitted in-line auto transformers in the leads of things like the TV. My Dad still has his B&D drill which had the windings changed, and the rating plate on the side has been over-stamped with the new voltage rating.

DC mains supplies were still available in some areas as a secondary supply up to 1980. University College London Physics department had 220VDC socket outlets in all the laboratories (in addition to standard 240VAC). I used it for running a carbon arc lamp for an experiment. This came from a DC mains supply, which was also used by the central London cinemas and theatres for arc lamps, and many buildings for DC lift and escalator motors.

The DC mains supply ceased sometime before 1983, and a large DC power supply was installed in the basement to maintain the DC circuits in the building for some key things that needed it (I suspect lifts and a giant flywheel UPS in the computer centre - although it was still provided to the labs, I doubt they alone justified it).

[charles]

[Snip]

If, like me, you were only in a 200v area for 3 years and then moved on, one or two things needed to be replaced. My coffee machine was one which did not like 240v. My Henley Solon worked very well for a couple of years, but then needed a new element. HiFi stuff had voltage change devices, so that was fine.

[Fredxxx]

Quite, which is why DC trumps AC, reduced heating through skin effect and a higher average current at a permanent maximum voltage rather than one that spend most of it's time at 2/pi Vmax.

No it's not. There is also the inductance to take into account.

[Fredxxx]

Are you suggesting that the inductance of the series motor is zero?

Even on a stalled motor? Are you suggesting the starting torque is the same for a universal motor working on AC and DC?

Have you ever considered why some DC motors don't have a laminated stator?

[The Natural Philosopher]

I think that says it all really. I say resistive load, you introduce inductance which I have clearly ruled out by saying resistive load.

wanker.

[Fredxxx]

Oh dear, you seem to be entirely ignorant of transmission lines and their inductive characteristics.

Only an idiot will think that a resistive load will cancel out transmission line inductance.

Best go away and recap on the things you seem to either have never known, or have simply forgotten.

Funny that, inductance being mentioned 15 times in the page.

Keep taking the solanezumab. Oh dear, it's been proven not to work!

[The Natural Philosopher]

Its has become the norm since 1960 for long hauls and undersea routes, but the norm in smaller grids is 100KV+ three phase overhead AC lines.

[The Natural Philosopher]

Golly, A word Counter.

WE were talking about losses.

Losses are down to resistance.

[Fredxxx]

While you might resort to counting, even a dummy knows that browsers tell you how many hits there are for a search item.

And resistance losses are lower for HVDC long distance transmission:

I don't expect you to understand why.

[The Natural Philosopher]

Sigh. Are you changing the subject *again*?

[Fredxxx]

Is that a final acceptance of your ignorance?

Have you already forgotten your reply of bollocks to this, convenient or otherwise:

"That's why AC ruled for so long. But now that silicon can handle HV downconversion, dc wins for long lines. DC stays at max voltage all the time, whereas ac is ever varying between zero and max voltage, so the dc line carries a lot more power over a given line."

[The Natural Philosopher]

The point is you have moved the goalposts from the general to the particular.

And the reason for using DC has NOTHING to do with power capacity.

[Fredxxx]

The goalposts were moved once you replied "bollocks". If you don't like subject wander then don't post abusive nonsense.

It has everything to do with the power capacity of a power transmission line. A HVDC transmission line gets more power to the destination than an AC line for the same size of conductors over long distances. Simply stop being in denial of the facts.

Do you still believe the inductance of a AC power transmission line affects the power it can transmit without expensive banks of capacitors?

Do you really still believe AC can be transmitted over long distances more efficiently than DC?

[Bob Eager]

But this statement WAS bollocks.

[Fredxxx]

And he continues to spot bollocks. Most intelligent people would simply give up when they are shown to be wrong, but NT is like Duracell and goes on and on spouting crap.

[rick]

I installed some Ward Leonard sets back in 70's ... factory now long gone, wonder if Ward Leonard control is still used ?