Lights going out momentarily

[waynemorrell]

Hi,

Wasn't sure where to post this one but here goes.

Was on a 508 into Chester yestarday and as we were going over Chester North Junction, as well as the usual squeeling from underneath the unit the lights went on and off a few times.

I assumed the unit lost contact with the third rail ?

Not having a go just wondered as haven't had it happen to me on DC stock unless it was bad weather.

I seem to remember it was common on the London Underground though. Is it still ?

Thanks!

 

[Bletchleyite]

There are quite large gaps in the third rail near Chester lined up such that you can end up with all the shoes briefly off power (sometimes known as "gapped", particularly if this causes the unit to be stranded and unable to move). It's quite unusual to get this effect on Merseyrail because unlike LU stock the units have bus lines (i.e. all the shoes in a 3-car set are connected together), whereas on LU there is no bus line so if one vehicle loses power the lights go off.

You do indeed still get it on older LU stock e.g. the Picc or Bakerloo. Indeed, it appears to be the case that on some old LU stock the lights on each side are powered independently from a different shoe.

 

[hexagon789]

Hi,

Wasn't sure where to post this one but here goes.

Was on a 508 into Chester yestarday and as we were going over Chester North Junction, as well as the usual squeeling from underneath the unit the lights went on and off a few times.

I assumed the unit lost contact with the third rail ?

Not having a go just wondered as haven't had it happen to me on DC stock unless it was bad weather.

I seem to remember it was common on the London Underground though. Is it still ?

Thanks!

It seemingly used to be very common on the Glasgow Subway pre-refurbishment due to the anachronistic the lighting supply was provided.

I have had it happen on a 314 but only once and I think it was a unit fault.

 

[185143]

I was always told this happened when a 508 entered a neutral section. Is this not the case? I know it happens when you cross into platform 3 at Hamilton Square too.

 

[Statto]

I was always told this happened when a 508 entered a neutral section. Is this not the case? I know it happens when you cross into platform 3 at Hamilton Square too.

Yep it's quite common on the Merseyrail network, especially into Hamilton Square P3.

 

[Elecman]

I was always told this happened when a 508 entered a neutral section. Is this not the case? I know it happens when you cross into platform 3 at Hamilton Square too.

You don’t have Neutral sections on DC Third Rail, you do have section gaps though.

 

[edwin_m]

It always used to happen with A Stock going into and out of Baker Street in the direction of Finchley Road, probably some of the most complex pointwork on the Underground and accompanied by sideways lurches over the turnouts if the train was platformed in one of the bays. Probably rather frightening to anyone not expecting it. However either here or on Merseyrail a couple of lights should stay on under battery power, and although I haven't been that way on S Stock I imagine their lighting is too sophisticated to have such problems.

 

[matt_world2004]

I remember it being really bad on the underground in the 90s it seemed to be that there would be periods where the whole carriage would go dark. Its a lot better now and I am curious how they delivered that improvement? Multiple shoe gears?

 

[hexagon789]

I remember it being really bad on the underground in the 90s it seemed to be that there would be periods where the whole carriage wouod go dark. Its a lot better now and I am curious how they delivered that improvement? Multiple shoe gears?

I'm guessing batteries, if you have the lights powered directly by batteries and the batteries charged by the shoe gear then if the supply was interrupted the lights would still stay on for a bit, hopefully long enough for the train to span the gap.

 

[AM9]

I'm guessing batteries, if you have the lights powered directly by batteries and the batteries charged by the shoe gear then if the supply was interrupted the lights would still stay on for a bit, hopefully long enough for the train to span the gap.

- and the fact that modern lighting draws much less current allowing continuous powering from such batteries. I would imagine that the 'S' stock has a bussed aux. power supply allowing services to be fed from any shoes that are receiving 750VDC (via inverters of course to prevent bridging gaps).

 

[hexagon789]

- and the fact that modern lighting draws much less current allowing continuous powering from such batteries. I would imagine that the 'S' stock has a bussed aux. power supply allowing services to be fed from any shoes that are receiving 750VDC (via inverters of course to prevent bridging gaps).

That too, also modern batteries are better anyway; they can be smaller and lighter but still do the job.

 

[Dstock7080]

I remember it being really bad on the underground in the 90s it seemed to be that there would be periods where the whole carriage wouod go dark. Its a lot better now and I am curious how they delivered that improvement? Multiple shoe gears?

Emergency lights, fed by the batteries, would still remain on. 50v tungsten bulbs at car-ends on 1938/‘56/‘59/‘62, A, CO/CP, R Stock; 110v fluorescent tubes on 1967/‘72/‘73/‘83/‘92/‘95/‘96, C, D Stock. Motor generators/alternators supplying main-car lighting was/is fed by track voltage.
Many systems were improved when trains were refurbished, D Stock going from two to four emergency lighting tubes.
2009 and S Stock indeed have a 400v bus-line for auxiliary circuits, which is why you rarely see these dim over gaps.

 

[Mojo]

You do indeed still get it on older LU stock e.g. the Picc or Bakerloo. Indeed, it appears to be the case that on some old LU stock the lights on each side are powered independently from a different shoe.

Indeed; part of the training for staff undergoing their checks on certain stocks in the event of certain defects is to look back through the cab door and if the main car lighting is extinguished on one side then it will assist you to determine whether the fault is at your end or the other end.

 

[hexagon789]

2009 and S Stock indeed have a 400v bus-line for auxiliary circuits, which is why you rarely see these dim over gaps.

Which is a vast improvement!

 

[greyman42]

It always used to happen with A Stock going into and out of Baker Street in the direction of Finchley Road, probably some of the most complex pointwork on the Underground and accompanied by sideways lurches over the turnouts if the train was platformed in one of the bays. Probably rather frightening to anyone not expecting it. However either here or on Merseyrail a couple of lights should stay on under battery power, and although I haven't been that way on S Stock I imagine their lighting is too sophisticated to have such problems.

Slightly of the subject. What caused the sideways lurches and how severe did it feel to the passengers? What is a turnout?

 

[hexagon789]

Slightly of the subject. What caused the sideways lurches and how severe did it feel to the passengers? What is a turnout?

A turnout is a set of points essentially

 

[edwin_m]

A turnout is in particular the diverging (non-straight) route over the points, which is what causes the sideways lurches.

 

[hexagon789]

A turnout is in particular the diverging (non-straight) route over the points, which is what causes the sideways lurches.

Ah, so it's specifically the route rather than the points?

 

[edwin_m]

Ah, so it's specifically the route rather than the points?

Yes, track engineers will sometimes refer to "turnout speeds".

 

[hexagon789]

Yes, track engineers will sometimes refer to "turnout speeds".

Ah, thank you for clearing that up, I wondered what the subtle difference might be.