Double third rail query

[Taunton]

Platform walls on the DLR have projecting shields above where the shoegear stops, to reduce the risk of something like a dropped umbrella coming into contact with it.

Now being extended to be the continuous length of the platform for the new trains, which presumably have different shoe positions. It's one of the downsides of bottom-contact that although the live rail itself can be shrouded, the shoes, including on the non-live rail side, commonly the platform side, are projecting upwards and live.

I've also seen trespassers cross between platforms (yes!) using the short shields as steps up.

 

[AlbertBeale]

Also why does the DSD always go off when departing Surrey Quays when the train hasn’t even been moving for 1 second yet to warrant an activation?

DSD?

 

[CarrotPie]

DSD?

Driver Safety Device - goes off if the dead man's pedal is no longer held down. Not to be confused with the DVD (Driver Vigilance Device), which goes off every 60 seconds unless the driver uses a control/button.

 

[D365]

What are the consequences of having two separate power supplies mix with each other through the cross connection? Both the ELL and Sussex line are 750V DC after all.

Nominally, yes. But in reality, it’s a very different story.

Driver Safety Device - goes off if the dead man's pedal is no longer held down. Not to be confused with the DVD (Driver Vigilance Device), which goes off every 60 seconds unless the driver uses a control/button.

Only if your traction has multi-resettable vigilance. Otherwise it’s lifting and resetting the pedal.

 

[Skoodle]

Also why does the DSD always go off when departing Surrey Quays when the train hasn’t even been moving for 1 second yet to warrant an activation?

It's the train fault alarm. There's a large third rail gap in the platform, so the train has a panic attack when stopped over it for too long.

 

[LBMPSB]

Traditional London Underground stock has no "Busbar" connection throughout the train like national 3rd rail trains do. So Electrical Section Gaps do not need to be the entire unit length. Because if the front of a train passes over the section Gap into a de-energised section, it cannot liven up the de-energised section via the traction shoes touching the de-energise rail at the front and having shoes on the live section in rear. I understand that Class 378 units have a 'A' end and a 'D' end, they are effectively two units in one. My question is, when the 'A' end and 'D' end are coupled together, is there a DC power supply linking the two halves, thus a bus bar effect, or are they not linked? In which case the Section Gap in the original post doesn't need to be a full unit length to be effective. I know of no special instructions other than the standard rules and regs (lifting shoe gear on Class 73 locos), we had at Three Bridges ROC on sending trains between the ROC and the OBC at New Cross Gate, whether normally or during engineering work when the third rail was switched off (isolated).

 

[contrex]

My question is, when the 'A' end and 'D' end are coupled together, is there a DC power supply linking the two halves, thus a bus bar effect, or are they not linked?

I am pretty certain that EMU inter-unit power jumpers have not been a thing since Southern Railway days and shortly after; the 4-SUBs had them. A few of the very early SR-style first 4-EPBs in 1951 were built with them, but they were removed and no more built with them fitted.

 

[LBMPSB]

I am pretty certain that EMU inter-unit power jumpers have not been a thing since Southern Railway days and shortly after; the 4-SUBs had them. A few of the very early SR-style first 4-EPBs in 1951 were built with them, but they were removed and no more built with them fitted.

I do not know if this is the case between units. But on EMUs, one unit is powered throughout, basically there is a live connection between the front coach and the rear coach, so if front shoes are on a dead section of thrid rail and the rear is on a live section, it will connect and liven the dead section. Which is why when current is switched off in an emergency Electrical Control Operators need to know what trains are affected and at what signals they are at, just in case they bridge a live section to a dead section, and why they use abutting switched off section to the section required to be isolated. But on London Underground it was always the case that there was no electrical power connection between any shoes on one coach of a unit to any other shoes on any other coach in the same unit, so if the front coach shoes were on a dead section, the rear coach shoes on a live setcion, the dead section would not be livened. Hence why London Underground have Third Rail Section Gaps to protect dead sections.

 

[TurboMan]

It's the train fault alarm. There's a large third rail gap in the platform, so the train has a panic attack when stopped over it for too long.

If the train is gapped, how does it move off from the station? Or is it because (unlike other Electrostars) the power unit line doesn't run the full length of the train?

 

[Tynwald]

508 and 455 had power jumpers. 507 didnt, because they worked underground single bore tunnels. When 508 tranferred to Merseyrail, the were removed. later 507 and 508 had them installed. As far as aware all southern emu had them fitted. EPB, CEP, CIG, REP, and so on.

 

[stuving]

Traditional London Underground stock has no "Busbar" connection throughout the train like national 3rd rail trains do. So Electrical Section Gaps do not need to be the entire unit length. Because if the front of a train passes over the section Gap into a de-energised section, it cannot liven up the de-energised section via the traction shoes touching the de-energise rail at the front and having shoes on the live section in rear. I understand that Class 378 units have a 'A' end and a 'D' end, they are effectively two units in one. My question is, when the 'A' end and 'D' end are coupled together, is there a DC power supply linking the two halves, thus a bus bar effect, or are they not linked? In which case the Section Gap in the original post doesn't need to be a full unit length to be effective. I know of no special instructions other than the standard rules and regs (lifting shoe gear on Class 73 locos), we had at Three Bridges ROC on sending trains between the ROC and the OBC at New Cross Gate, whether normally or during engineering work when the third rail was switched off (isolated).

This question of bridging was raised earlier in the thread, but not answered. From TfL's datasheet for the class 378, the shoes are on bogies 1,4,7, and 10. Their spacing is 35,20, and 35m, so 90m between the outer shoes of one unit. That gap at New Cross Gate is at most 74m. So if it does provide isolation between supply systems, the DC rails at the two ends of a 378 cannot be connected together.

For other stock, and in particular a classic 4x20m unit, the outer shoes would be spaced close to 74m. That could explain why this gap size was chosen, but for obvious practical reasons you'd want a standard size for the whole network. Is that the approach that has actually been taken?

When units longer than 80m arrive they will then need special measures, such as splitting the DC bus (as here) or perhaps moving the outer shoes in from the end bogies.

 

[edwin_m]

This question of bridging was raised earlier in the thread, but not answered. From TfL's datasheet for the class 378, the shoes are on bogies 1,4,7, and 10. Their spacing is 35,20, and 35m, so 90m between the outer shoes of one unit. That gap at New Cross Gate is at most 74m. So if it does provide isolation between supply systems, the DC rails at the two ends of a 378 cannot be connected together.

For other stock, and in particular a classic 4x20m unit, the outer shoes would be spaced close to 74m. That could explain why this gap size was chosen, but for obvious practical reasons you'd want a standard size for the whole network. Is that the approach that has actually been taken?

When units longer than 80m arrive they will then need special measures, such as splitting the DC bus (as here) or perhaps moving the outer shoes in from the end bogies.

This seems logical on the assumption that each 378 is split in two electrically, though noted there is no confirmation of this.

The gap length is most likely set by reference to the types of unit that are cleared to use the route, with the understanding that if other units ever visit they will need special measures of some sort. Using a network-wide figure to account for all possible units would probably mean the gap here had to be longer, which is an obvious inconvenience as well as a stranding risk considering it's just off the end of a platform. I know the 700s are split into two units electrically on AC and I assume on DC too, so the widest separation between electrically connected shoes on the network is probably either this or a five-car 444.

 

[CarrotPie]

508 and 455 had power jumpers. 507 didnt, because they worked underground [in] single-bore tunnels. When 508 tranferred to Merseyrail, the were removed. later 507 and 508 had them installed. As far as aware all southern emu had them fitted. EPB, CEP, CIG, REP, and so on.

Why does that mean no power jumpers?

 

[dgl]

I suppose a simple way to isolate shoes on a unit would be to stick diodes on them, as they would prevent any DC current flowing back.
Though whilst this would be simple there would be some voltage drop (so said diodes would probably need cooling, and efficiency would be further more reduced) on an already inefficient electrification system) the diodes would have to be quite large for the current required.

 

[Somewhere]

508 and 455 had power jumpers. 507 didnt, because they worked underground single bore tunnels. When 508 tranferred to Merseyrail, the were removed. later 507 and 508 had them installed. As far as aware all southern emu had them fitted. EPB, CEP, CIG, REP, and so on.

455s didn't/don't have power jumpers between units. Only within units. Same as all the CIGs/CEPs etc

 

[Sunset route]

deleted

 

[contrex]

I do not know if this is the case between units. But on EMUs, one unit is powered throughout, basically there is a live connection between the front coach and the rear coach, so if front shoes are on a dead section of thrid rail and the rear is on a live section, it will connect and liven the dead section. Which is why when current is switched off in an emergency Electrical Control Operators need to know what trains are affected and at what signals they are at, just in case they bridge a live section to a dead section, and why they use abutting switched off section to the section required to be isolated. But on London Underground it was always the case that there was no electrical power connection between any shoes on one coach of a unit to any other shoes on any other coach in the same unit, so if the front coach shoes were on a dead section, the rear coach shoes on a live setcion, the dead section would not be livened. Hence why London Underground have Third Rail Section Gaps to protect dead sections.

Yes. It's understood, I think, that most non-Underground third-rail EMUs have a DC bus line linking all the shoes within that unit. Where you seemed to be in doubt was whether that bus was continued between coupled units, via jumpers at the cab ends. The last widely used EMUs to have this were the 4-SUBs. Only depot staff could connect or disconnect the power jumpers, so 8-car formations tended to stay together all day. I believe that in very severe weather conditions, e.g. snow/ice and freezing fog, 8-SUB formations were sometimes used on London-Brighton runs & vice versa to get people home because they were less likely to come to a stand because of poor contact (heavy shoegear, and 8 linked shoes). I recall that the Met locos, Sarah Siddons and the, used to haul fixed sets of compartment coaches (called 'Dreadnoughts') that had shoegear at the ends, and a power line though, and jumpers to the loco, to avoid gapping. As far as I know, they didn't have control cabs, so either a spare loco would be needed to reverse, or the loco would have to run round.

I suppose a simple way to isolate shoes on a unit would be to stick diodes on them, as they would prevent any DC current flowing back.

Are you sure about this?

455s didn't/don't have power jumpers between units. Only within units. Same as all the CIGs/CEPs etc

Nothing after 1951 had jumpers between sets, and the few early EPBs that had them soon lost them. So no jumpers on EPBs, HAPs, CEPs/BEPs, CIGs/BIGs, VEPs, REPs, and later.

 

[edwin_m]

I suppose a simple way to isolate shoes on a unit would be to stick diodes on them, as they would prevent any DC current flowing back.
Though whilst this would be simple there would be some voltage drop (so said diodes would probably need cooling, and efficiency would be further more reduced) on an already inefficient electrification system) the diodes would have to be quite large for the current required.

I've an idea the 450s and 444s originally had diodes to prevent regeneration occurring, as that was outside their safety case until allowed some years later. These might have been between the power bus and the traction packages not the shoes. Diodes on the shoes would also prevent regenerative braking though, increasing power consumption by around 20%.

 

[D7666]

508 and 455 had power jumpers. 507 didnt, because they worked underground single bore tunnels. When 508 tranferred to Merseyrail, the were removed. later 507 and 508 had them installed. As far as aware all southern emu had them fitted. EPB, CEP, CIG, REP, and so on.

others have answered in between, but I think in general you are confusing inter-unit and intra-unit power jumpers. (I'll stick with the term jumper albeit not exactly the correct one).

units for working in tunnels /generally/ have no intra-unit jumpers i.e. each motor coach is /generally/ isolated from the other; when on DC 313s as built for Moorgates were all like this; when on AC as they were above ground and electrically coupled via the middle (transformer) coach; when some went to NLL etc a mod was done (to make them 313/1) that interconnected the two motor coaches within each unit.

508 as built and 455 had intra-unit jumpers - but never inter unit; no modern unit has, as has been posted here already, the last squadron fleet with inter unit power jumpers were 4Sub, initial 4EPB did but removed very early on. Every other main line unit I can think of (but see long units below) had intra unit jumpers.

Having said all that, there is a common myth that underground trains are not permitted intra-car power jumpers at all; this is not true, 1992 tube stock for example every car is a motor coach; there is one shoe set per pair of cars, traction does jump one car (with shoes) to the adjacent car (no shoes); what is not allowed is to daisy chain those pairs together. there are similar configurations on S stock.

Long units like 700s have no complete through intra-unit traction link; the two halves of a 700 - both 700/0 and 700/1 - are w.r.t. traction power, AC or DC, isolated from each other; one half fails it is dead, the unit is on half power; there is of course auxiliary / control power through the whole unit. The effect is a 700 is more or less two discrete coupled units. AIUI 345s and 10car 701s are similar but I don't know where the breaks are, if any; I assume a 10.701 is split symetrically 5/5, and a 9.345 split either side of the middle car that happens [or deliberately] to be a trailer. Anyone know for sure ?


I am not sure 444/450 diodes is correct; it is true they were not permitted to regen in their early days but IIMU was simply blocked within the traction pack software. TBH I had never heard of diodes used here before, it might be right, just saying I never heard of this before, nor do I understand why it would be needed when s/w blocking could do the same thing.

 

[stuving]

AIUI 345s and 10car 701s are similar but I don't know where the breaks are, if any; I assume a 10.701 is split symetrically 5/5, and a 9.345 split either side of the middle car that happens [or deliberately] to be a trailer. Anyone know for sure ?

Noted from a talk by Bombardier in 2016:

• Each train has two independently-powered ends and a trailer in the middle, so it will run with both pantographs up.
• There are 5 powered bogies (both axles in each) in a 4-car "half". One car with one powered bogie will be left out of each "half" in the interim 7-car units delivered next year for use on the ex-GE TfL-rail service.

Also, the centre trailer is allocated to one half or the other, arbitrarily - I guess along with the label 1 or 2, or A or B.

 

[hwl]

I suppose a simple way to isolate shoes on a unit would be to stick diodes on them, as they would prevent any DC current flowing back.
Though whilst this would be simple there would be some voltage drop (so said diodes would probably need cooling, and efficiency would be further more reduced) on an already inefficient electrification system) the diodes would have to be quite large for the current required.

And how would that work with regenerative braking which all the units in this area use? (Saving operators many £££s)

Long units like 700s have no complete through intra-unit traction link; the two halves of a 700 - both 700/0 and 700/1 - are w.r.t. traction power, AC or DC, isolated from each other; one half fails it is dead, the unit is on half power; there is of course auxiliary / control power through the whole unit. The effect is a 700 is more or less two discrete coupled units. AIUI 345s and 10car 701s are similar but I don't know where the breaks are, if any; I assume a 10.701 is split symetrically 5/5, and a 9.345 split either side of the middle car that happens [or deliberately] to be a trailer. Anyone know for sure ?

345 are 5-4 split with the middle vehicle being trailer so no traction power need there anyway.
701 is 5+5

I am not sure 444/450 diodes is correct; it is true they were not permitted to regen in their early days but IIMU was simply blocked within the traction pack software. TBH I had never heard of diodes used here before, it might be right, just saying I never heard of this before, nor do I understand why it would be needed when s/w blocking could do the same thing.

Software is used

 

[Skoodle]

If the train is gapped, how does it move off from the station? Or is it because (unlike other Electrostars) the power unit line doesn't run the full length of the train?

Apologies, I wasn't so clear in my earlier reply. One coach is off the juice in the station, so we get a yellow fault "MOS Loss of DC supply". It also happens approaching Old Kent Road Jn (towards Clapham). There's a large section gap on approach to the signal protecting the junction, so will often get alarms start blaring there too. Bit of a distraction risk whilst approaching a red!