Electricity for Trains

[securespark]

Call me an electrical geek, but I found this interesting.

 

[big-all]

as far as i know lots road shut down years ago
i was a driver on the southern from 76-94 and was a similar set up with 750v dc
you could shut off the power with a short circuit bar but not on the underground sections where B R and underground shared the tracks like wimbledon to putney the bar would just melt at they didnt have breakers that trip with a short

 

[securespark]

the bar would just melt

 

[winston1]

On shared sections how did they get round the different voltages used? Also the problem that the underground used a -ve return rail and BR used the running rails for return?

 

[securespark]

On shared sections how did they get round the different voltages used?

They used a transformer?

as far as i know lots road shut down years ago

That film was shot in 89.

 

[bernardgreen]

In the old days ( probably still today ) the were two bare copper wires running the length of the tunnels. Drivers could clip a phone onto these wires to talk to the signal box, if the wires were shorted or snapped then traction power would be cut off automatically.

 

[winston1]

In the old days ( probably still today ) the were two bare copper wires running the length of the tunnels. Drivers could clip a phone onto these wires to talk to the signal box, if the wires were shorted or snapped then traction power would be cut off automatically.

Indeed. You obviously did not watch the video.

 

[winston1]

They used a transformer?

If you haven't anything sensible to say I suggest you don't embarrass youself with stupid comments.

 

[securespark]

Fine sense of humour there, winnie!

 

[bernardgreen]

Indeed. You obviously did not watch the video.

No I didn't, low bandwidth connection.

 

[mfarrow]

Ref. shared areas, a lot of the time BR (and, now Network Rail) would drop their voltage on the shared line, or leave it alone if the train could manage the difference.

The key difference is that eg on Bakerloo line outside Queens Park (where NR take over) the voltages are 650V and 0V, ie there is no split voltage as found elsewhere. Plus, the 4th rail is invariably tied to the return running line to allow both types of train (Underground and Overground) to share the metals. Both use the 3rd (outer) rail to collect the 650VDC, its just how they return it that differs.

Short circuits should always cause the breakers to trip, by the way, so I'm not sure what's going on there.

 

[Deleted member 18243]

Wonderful film!

From the days when people spoke properly; wore shirts and ties to work and were called Cyril or George.

The only disappointment was that they didn't show the short circuiting bar actually making a short circuit; sparks and all!

 

[securespark]

Wonderful film!

From the days when people spoke properly; wore shirts and ties to work and were called Cyril or George.

It was only 1989!!

 

[big-all]

Ref. shared areas, a lot of the time BR (and, now Network Rail) would drop their voltage on the shared line, or leave it alone if the train could manage the difference.

The key difference is that eg on Bakerloo line outside Queens Park (where NR take over) the voltages are 650V and 0V, ie there is no split voltage as found elsewhere. Plus, the 4th rail is invariably tied to the return running line to allow both types of train (Underground and Overground) to share the metals. Both use the 3rd (outer) rail to collect the 650VDC, its just how they return it that differs.

Short circuits should always cause the breakers to trip, by the way, so I'm not sure what's going on there.

it was possibly to discourage us from doing it for some reason lol
maybe it was a bit different in 1976 ??
perhaps i misunderstood or my recollection from 40 years ago have let me down

ahh thinking about it you would have to drop the bar handle towards the fourth rail so maybe that what it was

 

[mfarrow]

@big-all Quite possibly... there are several factors at play.

In DC areas a lot of breakers are shunt magnetically actuated and don't incorporate a protection relay as such like the AC gear has. This can make them slower to operate than other switchgear.

Furthermore, the lowish voltages make DC areas more susceptible to volt drop especially on a fault from an LU 3rd/4th rail to running rail. So a fault can burn longer if a long way from the substation. I'm not sure how conductive LUs running rails can become (to DC) but it's clear that if you, for example, accidentally jumper from 3rd rail to running rail on an LU line you may have significantly less current pass than if you did that on NR infrastructure (so no breaker trip) but enough might flow to damage the bar and/or rails!