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General Vintage Technology Discussions For general discussions about vintage radio and other vintage electronics etc. |
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11th Sep 2018, 3:35 pm | #21 |
Tetrode
Join Date: Aug 2018
Location: Glasgow, Scotland, UK.
Posts: 55
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Re: Last public DC mains supply in the UK?
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11th Sep 2018, 4:04 pm | #22 |
Hexode
Join Date: Oct 2012
Location: London, UK.
Posts: 497
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Re: End of DC
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11th Sep 2018, 4:13 pm | #23 |
Hexode
Join Date: Jan 2012
Location: Weymouth, Dorset, UK.
Posts: 422
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Re: Last public DC mains supply in the UK?
I seem to remember that a friend of mine who was a radio officer on merchant ships told me that several of the vessels he was on had 220-440 volts DC some had 115 volts but at 400 cycles and one which was a passenger liner had 115 at 400 cycles and some 240 at 50 cycles for passenger use
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11th Sep 2018, 4:43 pm | #24 |
Nonode
Join Date: Jan 2010
Location: North Somerset, UK.
Posts: 2,129
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Re: Last public DC mains supply in the UK?
There must have been a lot of DC mains in 1947.
A severe coal shortage was disrupting electricity supplies, and to relieve matters, the Royal Navy used moored diesel electric submarines to supply DC power to some coastal towns. This was hated by the crews of the submarines as the continually running engines resulted in a freezing cold draught throughout the vessel. Google "operation blackcurrant" for more details. |
11th Sep 2018, 5:14 pm | #25 | |
Nonode
Join Date: Aug 2015
Location: Cambridge, Cambs. UK.
Posts: 2,196
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Re: Last public DC mains supply in the UK?
Quote:
https://www.radiomuseum.org/r/eddyst..._670as670.html I can imagine that a decent short-wave radio in the cabin might then have provided a greater variety of news and entertainment than the limited satellite TVs installed in today's cruise ships! Martin
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11th Sep 2018, 5:39 pm | #26 |
Heptode
Join Date: Jul 2016
Location: Portland, Dorset, UK.
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Re: Last public DC mains supply in the UK?
The manual for the Technics SA-X900L which must be late 80's does mention not to use this product on ships as it might be DC power, or words to that effect.
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11th Sep 2018, 5:41 pm | #27 | ||
Dekatron
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 7,061
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Re: Last public DC mains supply in the UK?
Quote:
Quote:
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11th Sep 2018, 6:14 pm | #28 | |
Nonode
Join Date: Oct 2008
Location: Warsaw, Poland and Cambridge, UK
Posts: 2,669
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Re: Last public DC mains supply in the UK?
Quote:
Chris
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11th Sep 2018, 6:28 pm | #29 |
Tetrode
Join Date: Aug 2018
Location: Glasgow, Scotland, UK.
Posts: 55
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Re: Last public DC mains supply in the UK?
Why not use a dynamo, as I assume was used before the 'invention' of AC?
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11th Sep 2018, 6:31 pm | #30 |
Dekatron
Join Date: Jan 2012
Location: Brentwood, Essex, UK.
Posts: 5,316
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Re: Last public DC mains supply in the UK?
I have been on a number of cruises in the last decade (my wife is very good at getting last-minute cut price offers), and AFAIR they have all had 60Hz AC supplies, even the ones built in European shipyards for European companies. In the staterooms, some have had 230V only, others both 230 and 120V sockets. Apart from an elderly Thomson vessel that only had the French sockets that will not accept a Schuko plug, most of the others have had UK 13A, Schuko, and US flat pin sockets. None had DC.
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11th Sep 2018, 6:52 pm | #31 | |
Nonode
Join Date: Aug 2015
Location: Cambridge, Cambs. UK.
Posts: 2,196
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Re: Last public DC mains supply in the UK?
Quote:
"I can't be doing with any of those new fangled glass bottle jobs - I've got to supply the trams with my station, and those tram motors need proper dynamos to drive 'em, especially when they all start up together after the St Leger!" Martin
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11th Sep 2018, 7:13 pm | #32 | |
Nonode
Join Date: Jan 2010
Location: North Somerset, UK.
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Re: Last public DC mains supply in the UK?
Quote:
Firstly a dynamo had to generate at the utilisation voltage which seldom exceeded 650 volts and was often 500 volts. This limited the distance between dynamo and load to a few miles. Consumers too far away had to be served by a rotary converter from 3 phase high voltage AC. As reciprocating steam engines gave way to steam turbines, Dynamos were not easy to build for the high speeds at which turbines are most economic. A dynamo with a maximum speed of say 800RPM required either a special low speed steam turbine, or reduction gearing, either of which added to costs complication and losses. By contrast an alternator could run at 3,000RPM. Since high voltage alternators were needed in any case to serve outlying districts via rotary converters, it became economic to standardise on generating AC only via modern large alternators driven by high speed steam turbines. The limited DC load was served by converting plant, with the losses being cheaper than separate DC generation. |
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11th Sep 2018, 7:23 pm | #33 | |
Nonode
Join Date: Aug 2015
Location: Cambridge, Cambs. UK.
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Re: Last public DC mains supply in the UK?
Quote:
For example, I know that, back in the day, trolleybus drivers in Doncaster tended to use the regenerative braking pedal. If MARs were to be used for the DC supply, presumably that reverse current would just have supplied the other buses on the route. A rotating machine supply, on the other hand, would have absorbed the power without difficulty. Martin
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11th Sep 2018, 8:21 pm | #34 |
Octode
Join Date: May 2003
Location: Belper Derbyshire
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Re: Last public DC mains supply in the UK?
I think most regenerative braking was just dumping the power through a series of big air cooled wirewound resistors on the roof rather than attempting to push power back through the overhead line.
Christopher Capener
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11th Sep 2018, 10:02 pm | #35 | |
Nonode
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Location: Papamoa Beach, Bay of Plenty, New Zealand
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Re: Last public DC mains supply in the UK?
I suspect that we’ve turned into an off-topic side-street. But briefly, the use of on-board resistors for electric braking is known as rheostatic or dynamic braking, not regenerative braking. The term regenerative braking is used solely where power is returned to the overhead line (or third rail in some railway cases). The MAR problem was usually dealt with by including resistor banks in the substations, switched in by voltage rise. There were some railway examples where substations had mercury arc inverters as well as rectifiers. For further reading, see:
The Regenerative Braking Story; Struan Jno T Robertson & John D Markham; Scottish Tramway & Transport Society & Venture Publications, 2006; ISBN 10 905304 161. The MAR problem is discussed on p.125. Also highly recommended: Electric Traction; A.T. Dover; Fourth Edition; Pitman, 1963. Electric Traction Handbook (Control); R. Brooks; Pitman, 1954. And this IEE paper: Railway Electric Braking; F. Whyman; Paper #983, 1950. Returning to the main theme: Quote:
Cheers, |
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11th Sep 2018, 10:25 pm | #36 |
Hexode
Join Date: Oct 2016
Location: Newport, South Wales, UK.
Posts: 278
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Re: Last public DC mains supply in the UK?
Pedantically, dumping the energy as heat is rheostatic braking. Sending it back into the supply for use elsewhere is regenerative.
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12th Sep 2018, 12:43 pm | #37 |
Hexode
Join Date: Jan 2012
Location: Weymouth, Dorset, UK.
Posts: 422
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Re: Last public DC mains supply in the UK?
I think the reason why a rotary converter was used instead of a mercury vapor rectifier has more to do with what was available at short notice when the station DC generators were no longer usable for whatever reason. I'm thinking that when they knew the generators were sick they just went with the first available options to keep customers on load. I imagine it wouldn't go down well if the supply was suddenly cut off for a week or more. Some lifts have big wire wound resistors to absorb the motors back EMF when the lift comes to its floor and the brakes are applied I guess the same principle as trains trams and trolleybuses just a bit smaller scale.
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12th Sep 2018, 1:14 pm | #38 | ||
Dekatron
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Location: Penrith, Cumbria, UK.
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Re: Last public DC mains supply in the UK?
Quote:
Quote:
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13th Sep 2018, 7:35 pm | #39 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
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Re: Last public DC mains supply in the UK?
A rotary - coupled to a dirty great flywheel - had the benefit of damping-out short-term peaks and troughs of demand and so delivering a much better-regulated supply. "Industrial" loads are notorious for suddenly demanding massive current to get up to speed but then once everything's moving needing much less power.
Think something like mine winding-gear accelerating a few hundred tons of coal up a pit-shaft, or starting a half-mile-long conveyor-belt transporting those hundreds of tons of coal to the waiting rail-wagons. One of my relatives was chief-engineer to the Nottingham coalfields in the 1960s: they ran their own DC generating-plant to deal with the heavy/peak loads because the National Grid wasn't up to it. The Grid provided the 'background' power for continuous-loads like pumping water from the mines [daily ventilating and shifting tens of millions of gallons of water from deep mines is energy-intensive] but they still had their own DC generating-plant so they could continue to operate when the Grid couldn't handle the load. |
16th Sep 2018, 11:21 pm | #40 |
Nonode
Join Date: Jan 2010
Location: North Somerset, UK.
Posts: 2,129
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Re: Last public DC mains supply in the UK?
Also, a rotary converter will run correctly on no load, or virtually no load.
On a summer bank holiday, the load on a DC main supplying say 200 households could easily drop to a amp or so, out of a normal load of hundreds of amps. A rotary might be very inefficient at such low load, with perhaps 10KW or 20KW of losses whilst supplying 2KW, but it would work and reliably supply the consumer. A mercury arc would probably go out or at least become unstable. |