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Old 26th Feb 2012, 10:46 am   #1
Chris Parry
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Default DC/AC Mains Switchover: Southampton

As a kid, we lived in Southampton (near The Common) at the time of the big switchover. I well remember the lorry with all the new appliances the housewives could have if, for some reason, their old ones were unsuitable. I also remember the dirty smuts on the washing, a problem which stopped at the time of the switchover. The date will have been 1958 to 1963. But when exactly, and where was the old DC power station located, please? I also wonder if other cities were earlier or later than Southampton.
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Old 26th Feb 2012, 12:05 pm   #2
broadgage
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Default Re: DC/AC Mains Switchover: Southampton

Towards the end of DC days, many districts no longer had a DC power station, the DC current being obtained by converting plant from AC supplied by the national grid.
The lack of dirty smuts on washing might suggest the closure of a local power station, but could have had some other cause such as neighbours abandoning coal fires in favour of electric heating.

DC at utilisation voltages, typicly 3 wire DC at 240/480 volts, cant be economicly transmitted more than a mile or so.
DC generation therefore had to be very local indeed, fine in the early days but not very practical as the load and district served grew.
Rather than build new DC generating plant, it was the usual practice to generate AC also at higher voltages to serve outlying areas.
Nearer the point of use this high voltage AC supply was either transformed down to AC at utilisation voltage, or was converted to DC.
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Old 26th Feb 2012, 12:43 pm   #3
Chris Parry
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Default Re: DC/AC Mains Switchover: Southampton

This makes perfect sense. Thankyou for educating me! There were a lot of changes around about that time in Southampton. The trams had already gone, but now the gas street lamps were replaced by electric ones, and some of the houses had wiring installed for the very first time. My grandparents had earlier lived in Penarth, where they had bought a posh Marconi radio which travelled with them when they moved to Southampton. It then lived in the attic until the DC/AC switchover day. I remember it being switched on and they were lucky: it worked, no problem! Chris
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Old 26th Feb 2012, 1:00 pm   #4
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Default Re: DC/AC Mains Switchover: Southampton

Southampton's DC power station stood adjacent to Central Station. Presumably it was the same one as owned by Southampton Electric Light and Power Co., which was eventually taken over by the corporation and beefed up to supply the electric trams when they took over from horse traction.
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Old 26th Feb 2012, 1:11 pm   #5
Alan Stepney
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Default Re: DC/AC Mains Switchover: Southampton

According to the Trader Year Book, 1955, Southampton had 200v DC & 200/240v AC at that time.
(240 towns still had DC supplies.)

An earlier reference (1935) showed Southampton Corp. as the supply company, with three different supplies (presumeably different power stations).
1) 200v & 400 v DC
2) 200v & 240v AC (50 cycles) 1, 2 and 3 phase available.
3) 380v & 415v AC (50 cycles)
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Old 26th Feb 2012, 2:11 pm   #6
Chris Parry
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Default Re: DC/AC Mains Switchover: Southampton

That's a remarkable number of towns still running on DC in 1955. I wonder when DC power distribution finally died out in the UK. In Southampton as in many other cities, the line of tram posts is still to be seen along The Avenue, which is an unusually long and straight major road. Thanks for clarifying the location of the old DC power station. That's an area of the city that has been modernised/butchered a lot in the last 50 years. Chris.
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Old 26th Feb 2012, 2:13 pm   #7
Framer Dave
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Default Re: DC/AC Mains Switchover: Southampton

The 1965 edition of the Electricity Supply Handbook shows the following supplies:

1. 200/346V AC
2. 240/415V AC
3. 200/400V DC

Regards,
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Old 26th Feb 2012, 3:24 pm   #8
Darren-UK
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Default Re: DC/AC Mains Switchover: Southampton

Southampton's trams were withdrawn in 1949 and would've operated from the pretty-much-standard tramway voltage of 500/550VDC.

So what would've happened when the trams went? Would there have been dedicated generators for the tramways which were simply decommissioned after 1949? Or could the same generators have continued is use for the 200/400VDC supply mentioned above by Dave? Perhaps that question sounds daft but I'm not too clued up on the workings of power stations; presumably DC generators were used rather than AC with the output rectified and transformed.

It's perhaps ironic that DC returned to Southampton in 1967 when the railway was electrified but with the National Grid supplying power. That's not relevant here though, of course.
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Old 26th Feb 2012, 3:37 pm   #9
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Default Re: DC/AC Mains Switchover: Southampton

After the trams were withdrawn, Southampton Corporation ran a fleet of Guy Arab double-deckers. I think most were 4-cyl but there were some 6-cyl versions with the radiator a few inches further forward. The old tramshed was a substantial building next to The Avenue. In my day, it was used as a Corona depot but in later years it became an arts centre. The tram rails in there lasted for ages, but long gone now. I have no idea what they did with the old tram DC supply system, but it may well have been linked to the DC urban supply.

BTW: because of all the heavy shipping and the industry all along the docks, AM radio reception was particularly difficult in Southampton. Many homes were fitted for Rediffusion to overcome the intereference. It worked well.

Chris.
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Old 26th Feb 2012, 3:50 pm   #10
Lucien Nunes
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Default Re: DC/AC Mains Switchover: Southampton

Southampton Guildhall was wired for 3-phase AC supply when built in 1937, there are a few pieces of AC switchgear from that date still in service there.

Major customers with large installed DC plant inventories resisted change for quite a long time. Lifts, pumps, presses, lots of motor-driven loads were served by DC mains long after AC was available and preferred for domestic customers. For example, DC power was being supplied in NYC until 2007: http://www.coned.com/newsroom/news/pr20071115.asp

Some DC central stations had separate plant for traction and general supplies, others had sets that could be switched to either duty. I recovered some 210V DC passenger lifts from St. Pancras Chambers in London that were fed from a nearby DC converter station until about 1981, possibly powered from a traction supply. It was thought that other loads had been run from the DC up to that point, when the rotaries were unfortunately scrapped. There have been cases of isolated medium-voltage DC consumers being put directly onto the traction supplies, only getting power during the hours of public transport operation.

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Old 27th Feb 2012, 12:55 am   #11
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Default Re: DC/AC Mains Switchover: Southampton

HI this is very interesting .Here in weymouth our DC power station was de commisioned in 1966 does anyone know what voltage it gave? This station gave DC and AC at the same time athough the AC side was also closed when poole powerstation was opened. In those days the town was supplied at 33Kv from poole cheers all Hannah
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Old 27th Feb 2012, 10:12 am   #12
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Default Re: DC/AC Mains Switchover: Southampton

In the relatively early days of electric trams, DC generating plant was invariably used. As others post this was normally at about 550 volts.
Often the same dynamos could be used to supply public mains at 3 wire DC at 240/480 or 220/440 volts.
Towards the end though, most DC generating plant was scrapped and DC for tramways was obtained either by rotary converters or by transformers and mercury arc rectifiers, from AC supplies.

DC tramway supplies also used "negative boosters" .
The single overhead wire was invariably positive, with the return current passing through the running rails.
Voltage drop in the overhead wire was of relatively little concern as the traction equipment was designed to work over a wide voltage range.
Voltage drop in the return circuit of the running rails was of much greater concern, remember that these rails could be touched by the hooves of horses and by unshod humans. Buried pipes would also be corroded by any significant voltage between the running rails and true earth.
There was therefore a legal limit on the maximum permited voltage between the running rails and true earth.
The negative booster therefore "sucked" the current from the running rails and forced it into an insulated return conductor. The machine consisted of a motor driving a dynamo, the dynamo field was connected in series with the positive overhead wire.
The greater the current used for traction, the greater the voltage developed by the negative booster. It was usual to adjust the machine such that at the point of connection to the running rails, the voltage would be at the maximum permitted negative voltage. At the farthest point it would be the maximum permitted positive voltage.
Similar regulations applied to DC railways (and still do) but the permitted voltage is higher as the rails are not readily touched, and are partialy insulated by mounting on wood or concrete sleepers.
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Old 27th Feb 2012, 11:05 am   #13
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Default Re: DC/AC Mains Switchover: Southampton

And attached is a nice schematic that supplements broadgage's excellent description of the booster system for DC supplies.

Cheers,
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Old 27th Feb 2012, 12:57 pm   #14
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Default Re: DC/AC Mains Switchover: Southampton

Quote:
Southampton Corporation ran a fleet of Guy Arab double-deckers. I think most were 4-cyl but there were some 6-cyl versions with the radiator a few inches further forward.
I think the 150 Guy Arab buses all had Gardiner 6 cylinder engines (6LW). The chassis were built so that either the longer 6LW engine could be fitted or the smaller 5LW. the 4LW engine would not have pulled the skin off a rice pudding if fitted in a double decker. all of them had Park Royal Bodies (H30/26R)
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Old 27th Feb 2012, 2:26 pm   #15
Chris Parry
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Default Re: DC/AC Mains Switchover: Southampton

I know a lot more about Southampton now, thanks to all the replies on this thread! The negative booster malarkey strickes me as very cunning. I bet it worked perfectly, too.

Chris Parry (in Waterlooville near Portsmouth nowadays.)
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