120 V 230 Volts mains, which is best?

[ppppenguin]

I suspect all the lighting on trains, trams and buses these days is fed from switchmode PSUs which stabilise the output against a very wide input variation.

ISTR that in the old days the filament lamps (50V rated?) on tube trains were in series strings across the main 660V traction supply. Apart from a few which were on a battery to provide emergency lighting.

Which reminds me of some very ordinary looking GLS bulbs in a box at the Vintage Wireless Museum that I found many years ago. Never actually played the prank of putting one in an ordinary mains fitting. They were rated at 6V, 25W

[ed731pdh]

So were the heaters on the Southern rail slam door stock, 3 x 250v heaters wired in series across the line volts, but you'd loose all three if a single heater element blew.

Apparently 650DC for light railway systems is more cost effective and easily controllable. However, one of the oddest I ever heard of was on a railway in Southern Africa, think it was the Namib, which was wired for 25kv but the locomotives had MG sets fitted as the volts in some of the more remote sectors from the feeder substation dropped down to as little as 16kv and the aux feeds from the transformers would brown out.

[Terry]

When I was on the London underground & southern electrics many years ago the lights would dim & brighten when accelerating as the starting  resistances were switched in & out. 

Most of the Underground trains I used when I was at school in the late 50s had fluorescent lighting with one incandescent light at each end of the coach. Every time the train went over a section gap, all the fluorescents went  out, leaving just the battery backed incandescents alight. The fluorescents would all then strike again after the car cleared the gap.

Before it was rebuilt with flyovers and underpasses to completely segregate BR from LT tracks, the approaches to Barking station were just one large mass of surface crossings so, no sooner would all the lights come back on, they would go off again! In the dark it was like one long firework display!

[Hartley118]

Most of the Underground trains I used when I was at school in the late 50s had fluorescent lighting with one incandescent light at each end of the coach. Every time the train went over a section gap, all the fluorescents went  out, leaving just the battery backed incandescents alight. The fluorescents would all then strike again after the car cleared the gap........

I was always fascinated by those fluorescents operating on DC.  ISTR the tubes were connected in series across the 600V supply with a single resistive ballast.  Presumably the ballast had to be high enough resistance to stabilise the series circuit with reasonably constant current.  With the tube discharge having its usual negattive resistance, the design solution for ensuring economical balanced operation of series-connected tubes has never been obvious to me, unless of course they used a few KT66s providing constant current .

The classic discharge striations as the line voltage fell could be very entertaining.  There was also the uneven blackening of the tube, I guess due to evaporated tungsten ions migrating from the filaments to the negative terminal.

Such a lot of physics to ponder on one underground journey!  Are there any DC-operated fluorescents left for the delight of the next generation of physiscists?

Martin

[ppppenguin]

I think that some early fluorescents running on DC were provided with a reversing switch to even up the blackening. Or you could simply reverse the tube every so often.

I grew up on the Northern Line with 1938 class trains. None of the new fangled fluorescents that I can recall.
https://en.wikipedia.org/wiki/London_Und...inside.jpg

Nice comfy proper tube trains with lots of clicky noises from the motor controllers. There's a preserved set of 1938 at the Acton depot museum.

[colly0410]

I'm wondering if the USA has sort of the best of both worlds i.e. 120 volts for small gubbins & 240 volts for big gubbins. I wonder if they would ever drift over to using 240 volts for smaller gubbins like seems to have happened on the continent? What was the last European country to use 110 volts & when?

[ed731pdh]

It scares me when we have such a thing as a ring main, and the US are still doing individual fuse/breaker to point.

[Terry]

As far as I know, the ring main is a UK only phenomenon, devised after WWII to economise on the use of copper, which was in very short supply. I don't think it is used anywhere else.

[ppppenguin]

Ring topology is widely used in the distribution network, especially at 11kV.

[colly0410]

Remember reading somewhere that ring mains can only be safely used with fused plugs otherwise a faulty short circuited gubbins would get the full 30 amps, wereas with a 13 or 3 amps fused plug the max current would be err 13 or 3 amps in theory..