|
|
Post by spsmiler on Dec 22, 2019 17:08:51 GMT
It is a surprise to hear that a full length S7 could be gapped (a solo locomotive would be something else), maybe there were some power collection shoes missing?
|
|
|
|
Post by MoreToJack on Dec 22, 2019 17:33:03 GMT
It was an S8. The amount of pointwork in the Baker Street area makes it very easy for trains to be gapped.
|
|
class411
Operations: Normal
Posts: 2,743 
Member is Online
|
Post by class411 on Dec 22, 2019 18:21:11 GMT
It was an S8. The amount of pointwork in the Baker Street area makes it very easy for trains to be gapped. This is quite confusing for a layman. Surely no driver is going to stop in that area electively, only if instructed to do so by a signal. And surely the signal positioning would take potential gapping into account? Or is this down to a driver approaching a signal too slowly so that the train's inertia is insufficient to carry it over a gap? |
|
Chris M
Global Moderator
Forum Quizmaster
Always happy to receive quiz ideas and pictures by email or PM
Posts: 19,762
|
Post by Chris M on Dec 22, 2019 19:10:48 GMT
Not necessarily approaching a signal in the traditional sense. My understanding of CBTC is that the driver is given movement authority until a given point (which may or may not correspond with where a traditional signal would be) and a target speed - the speed at train in ATO would aim to travel the entire section at and which should (must?) not be exceeded. This is not necessarily the same as the maximum safe speed over the given piece of track depending how far in front the next train is (and what speed it is travelling at?)
|
|
Colin
Advisor
My preserved fire engine!
Posts: 11,346
|
Post by Colin on Dec 22, 2019 19:57:59 GMT
It is a surprise to hear that a full length S7 could be gapped (a solo locomotive would be something else), maybe there were some power collection shoes missing? It was an S8. The amount of pointwork in the Baker Street area makes it very easy for trains to be gapped. This is quite confusing for a layman. surely the signal positioning would take potential gapping into account? Or is this down to a driver approaching a signal too slowly so that the train's inertia is insufficient to carry it over a gap? In the context of S stock, when we talk about trains being gapped it's not neccessarly the case that the train is gapped electrically. I haven't had time to look into what happened so I may be barking up the wrong tree on this particular occasion, but it is highly unusual for an S7 or S8 to end up with all shoes off traction current. What usually happens when an S stock is gapped is that both driving motors have their pick up shoes off current; the problem is that whilst most electrical circuits on an S stock are on a continuous buss line, the compressors are only fed from their respective driving motor cars. So it dosen't matter if the middle motor shoegear cars are on traction current - if both driving motor cars are off current and the air drops too low, the train is effectively gapped as no air equals no movement. |
|
|
|
Post by philthetube on Dec 23, 2019 8:35:38 GMT
This is quite confusing for a layman. Surely no driver is going to stop in that area electively, only if instructed to do so by a signal. And surely the signal positioning would take potential gapping into account? Or is this down to a driver approaching a signal too slowly so that the train's inertia is insufficient to carry it over a gap? Sorry guys, just re read the thread and realised that I had written rubbish. Mods please feel free to delete post. |
|
|
|
Post by brigham on Dec 23, 2019 8:55:53 GMT
What usually happens when an S stock is gapped is that both driving motors have their pick up shoes off current; the problem is that whilst most electrical circuits on an S stock are on a continuous buss line, the compressors are only fed from their respective driving motor cars. Difficult to see how the compressors could be fed separately from the traction bus cables, other than by deliberate design. Are the bus cables perhaps for lighting only? |
|
Colin
Advisor
My preserved fire engine!
Posts: 11,346
|
Post by Colin on Dec 23, 2019 10:50:11 GMT
You can believe it or not; I’m only an Instructor Operator but I would have thought that was qualification enough.
I’m not going into a full technical explanation but it is a deliberate design. Traction current is fed via the pick up shoes on a DM (driving motor) car to a box known as the ACM (auxillary converter module). There are two ACM’s per S stock train; one on each DM car.
The ACM’s distribute power around various circuits and one of those is a direct feed to the compressor on the same DM car.
It is because the compressors are directly fed from the ACM on the same car that at least one of the DM cars must be on traction current in order to produce air.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Dec 23, 2019 10:51:32 GMT
Sorry guys, just re read the thread and realised that I had written rubbish. Mods please feel free to delete post. Your wish was granted |
|
|
|
Post by brigham on Dec 24, 2019 8:48:22 GMT
You can believe it or not; I’m only an Instructor Operator but I would have thought that was qualification enough. I’m not going into a full technical explanation but it is a deliberate design. Traction current is fed via the pick up shoes on a DM (driving motor) car to a box known as the ACM (auxillary converter module). There are two ACM’s per S stock train; one on each DM car. The ACM’s distribute power around various circuits and one of those is a direct feed to the compressor on the same DM car. It is because the compressors are directly fed from the ACM on the same car that at least one of the DM cars must be on traction current in order to produce air. Thanks for the confirmation. I wonder what advantage this arrangement gives, clearly of such magnitude as to outweigh the very real risk of 'gapping'? |
|
|
|
Post by t697 on Dec 24, 2019 9:09:56 GMT
You can believe it or not; I’m only an Instructor Operator but I would have thought that was qualification enough. I’m not going into a full technical explanation but it is a deliberate design. Traction current is fed via the pick up shoes on a DM (driving motor) car to a box known as the ACM (auxillary converter module). There are two ACM’s per S stock train; one on each DM car. The ACM’s distribute power around various circuits and one of those is a direct feed to the compressor on the same DM car. It is because the compressors are directly fed from the ACM on the same car that at least one of the DM cars must be on traction current in order to produce air. Thanks for the confirmation. I wonder what advantage this arrangement gives, clearly of such magnitude as to outweigh the very real risk of 'gapping'? Whatever you think about the design policy, S stock is not really different in this respect to most LUL trains from 1973TS onwards. Trains formed from single ended units of 1973TS, D78 stock and then the 95TS, 96TS, 09TS and S stock have two compressors and need the DM car local to the compressor to have a traction supply so that the compressor can run. Current rail layouts are as far as practicable laid out so both DM cars don't get gapped at the same time, but this is not always possible. Maybe alterations will be possible here, I don't know. After a signalling and track modification a couple of Christmases ago at Earl's Court something similar happened and the conductor rails were modified to prevent it. |
|
|
|
Post by underover on Dec 24, 2019 12:22:04 GMT
Put in very simple terms (I have never worked on S stock but this applies to most stocks I would imagine), 630V is not traditionally permitted to be passed though couplers. There are exceptions to this, so for example in order to rail a train at a depot, the front car needs to be on juice. The compressor is normally not on the DM of the train, so power needs to jump from one car to another and it does this though jumper cables. If you had a train consisting of 2 units, 630V is able to jump between cars (via jumpers), but not units because units are electrically connected though the pins on the coupler.
I imagine S stock are still somewhat seen as having a 'split', so you may find similar to other stock, 630V is only able to be passed between cars up until this split, even if there are no electrical connections via pins somewhere in the formation.
|
|
Dstock7080
Administrator
Posts: 5,805
Member is Online
|
Post by Dstock7080 on Dec 24, 2019 12:45:32 GMT
I imagine S stock are still somewhat seen as having a 'split', so you may find similar to other stock, 630V is only able to be passed between cars up until this split, even if there are no electrical connections via pins somewhere in the formation. On S Stock the 750v/630v supply is only passed between two adjacent cars. A 400v auxiliary bus-line is available between all cars, until a ‘middle’ bridging relay. |
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Dec 24, 2019 13:02:48 GMT
I imagine S stock are still somewhat seen as having a 'split', so you may find similar to other stock, 630V is only able to be passed between cars up until this split, even if there are no electrical connections via pins somewhere in the formation. On S Stock the 750v/630v supply is only passed between two adjacent cars. A 400v auxiliary bus-line is available between all cars, until a ‘middle’ bridging relay. Not when they were testing one at Harrow on the Hill when the train op accepted the wrong route and the section ahead got energised by the train. Hence why now they have big buffer sections for when testing takes place but I’m led to believe the issue has now been sorted by Bombardier |
|
North End
Beneath Newington Causeway
Posts: 1,769
|
Post by North End on Dec 24, 2019 14:36:25 GMT
You can believe it or not; I’m only an Instructor Operator but I would have thought that was qualification enough. I’m not going into a full technical explanation but it is a deliberate design. Traction current is fed via the pick up shoes on a DM (driving motor) car to a box known as the ACM (auxillary converter module). There are two ACM’s per S stock train; one on each DM car. The ACM’s distribute power around various circuits and one of those is a direct feed to the compressor on the same DM car. It is because the compressors are directly fed from the ACM on the same car that at least one of the DM cars must be on traction current in order to produce air. Thanks for the confirmation. I wonder what advantage this arrangement gives, clearly of such magnitude as to outweigh the very real risk of 'gapping'? It's not so much a case of advantage but necessity - having a through 630v line through the train is prohibited (for Tube stock at least, I'm not sure whether this would apply to surface stock). LU require at least two compressors on the train, and whilst these aren't generally located on the driving cars simply for reasons of space, there's good reasons why the feed comes from the driving cars. Shoegear is a pain for a start, so it's undesirable to have separate shoegear - and associated protection equipment like line breakers - on the trailer cars. Secondly having the feed come from the driving cars makes it easier for drivers to attempt to stop on current, and in depots it's essential as standard practice is to leave one car hanging out of the shed to haul the whole train onto current, otherwise it would be necessary to use leads all the time which again is highly undesirable. Gapping just the driving cars in reality isn't normally a major problem - as you will still have the middle motor cars on current which should be quite sufficient to get the train moving again. Losing the compressors isn't an immediate problem as the air is stored in reservoirs so there's no problem until this starts to deplete, and likewise the auxiliaries are fed by batteries so again this isn't an immediate problem. Speaking simply from experience, the most common problem is incorrect driver response in one of two ways - failing to recognise that the train has started to go into load-shed (which the modern stocks start to do in order to preserve battery life) and then going down the wrong defect-handling route, and/or wasting air and avoidably depleting main line air until the air has run out. I can think of a fair few incidents where one or both these things have happened, ultimately resulting in an avoidable long sit-down. |
|
|
|
Post by firestorm on Dec 24, 2019 16:51:35 GMT
Gapping just the driving cars in reality isn't normally a major problem - as you will still have the middle motor cars on current which should be quite sufficient to get the train moving again. Losing the compressors isn't an immediate problem as the air is stored in reservoirs so there's no problem until this starts to deplete, and likewise the auxiliaries are fed by batteries so again this isn't an immediate problem. This is where the S-Stock seems to throw every other normal rolling stock rules out the window. As Colin has mentioned with slight corrections, the auxillary converter module (ACM) is located on the second M1 car, this is probably one of the most important components on the train, it gets the 630V/750V from the leading DM (Driving motor) car, so it can convert the different voltages needed for the train e.g. 110v DC, 400v AC for the compressor (located back on the DM car). In a scenario where the front DM car is off juice so the ACM isn't running, but rear DM car is still on juice, the train goes into "bridging mode" where 400v AC can be supplied to the front compressor so effectively you have 2 compressors running off one ACM and vice versa. It is because of the way the S-Stock is designed, we can see major problems if both the front and rear DM cars are off juice, no active ACM's means no compressors. The middle cars being on current means nothing on a S-Stock, they are not connected to the ACMs in any way nor can be "bridged" to do so, their only purpose is to run their own and adjacent motor converter modules (MCM). The batteries are there to stop the train going into complete darkness and shutting down when the train is fully gapped, so if and when you are running on battery power alone, it's quite an urgent scenario. |
|
North End
Beneath Newington Causeway
Posts: 1,769
|
Post by North End on Dec 24, 2019 17:30:02 GMT
Gapping just the driving cars in reality isn't normally a major problem - as you will still have the middle motor cars on current which should be quite sufficient to get the train moving again. Losing the compressors isn't an immediate problem as the air is stored in reservoirs so there's no problem until this starts to deplete, and likewise the auxiliaries are fed by batteries so again this isn't an immediate problem. This is where the S-Stock seems to throw every other normal rolling stock rules out the window. As Colin has mentioned with slight corrections, the auxillary converter module (ACM) is located on the second M1 car, this is probably one of the most important components on the train, it gets the 630V/750V from the leading DM (Driving motor) car, so it can convert the different voltages needed for the train e.g. 110v DC, 400v AC for the compressor (located back on the DM car). In a scenario where the front DM car is off juice so the ACM isn't running, but rear DM car is still on juice, the train goes into "bridging mode" where 400v AC can be supplied to the front compressor so effectively you have 2 compressors running off one ACM and vice versa. It is because of the way the S-Stock is designed, we can see major problems if both the front and rear DM cars are off juice, no active ACM's means no compressors. The middle cars being on current means nothing on a S-Stock, they are not connected to the ACMs in any way nor can be "bridged" to do so, their only purpose is to run their own and adjacent motor converter modules (MCM). The batteries are there to stop the train going into complete darkness and shutting down when the train is fully gapped, so if and when you are running on battery power alone, it's quite an urgent scenario. So in the scenario of: - Both driving cars off current - All middle cars on current - Sufficient main line air - Batteries not dead What stops an S stock moving? On something like a 95 or 96 stock the only thing would be load-shedding, and there's a solution to that. On 95/96 stock the only difference versus an S stock seems to be that the compressor is fed directly instead of going through the auxiliary converter, however in practice this isn't really much different as on a 95/96 stock if anything goes wrong with either the traction on the driving car, compressors or auxiliaries than the line contactors will open and all these are lost on that unit (leaving only the traction packages on the middle motor car). If everything goes to plan in this situation the train will cross-feed (just like an S stock apparently does), but one has to hope nothing goes wrong with the other unit. So many times this has happened where a fault has developed on one half of the train and the driver hasn't responded correctly, and then something has happened on the good half - at which point it's a case of which comes first, air running out or the train going into load-shed! |
|
|
|
Post by firestorm on Dec 24, 2019 17:40:22 GMT
This is where the S-Stock seems to throw every other normal rolling stock rules out the window. As Colin has mentioned with slight corrections, the auxillary converter module (ACM) is located on the second M1 car, this is probably one of the most important components on the train, it gets the 630V/750V from the leading DM (Driving motor) car, so it can convert the different voltages needed for the train e.g. 110v DC, 400v AC for the compressor (located back on the DM car). In a scenario where the front DM car is off juice so the ACM isn't running, but rear DM car is still on juice, the train goes into "bridging mode" where 400v AC can be supplied to the front compressor so effectively you have 2 compressors running off one ACM and vice versa. It is because of the way the S-Stock is designed, we can see major problems if both the front and rear DM cars are off juice, no active ACM's means no compressors. The middle cars being on current means nothing on a S-Stock, they are not connected to the ACMs in any way nor can be "bridged" to do so, their only purpose is to run their own and adjacent motor converter modules (MCM). The batteries are there to stop the train going into complete darkness and shutting down when the train is fully gapped, so if and when you are running on battery power alone, it's quite an urgent scenario. So in the scenario of: - Both driving cars off current - All middle cars on current - Sufficient main line air - Batteries not dead What stops an S stock moving? On something like a 95 or 96 stock the only thing would be load-shedding, and there's a solution to that. In this scenario nothing, the middle cars would easily give enough traction to move the train. But it's one of those worst case scenarios where you have a perfect storm of everything seemingly to go wrong at the same time. |
|
North End
Beneath Newington Causeway
Posts: 1,769
|
Post by North End on Dec 24, 2019 17:54:59 GMT
So in the scenario of: - Both driving cars off current - All middle cars on current - Sufficient main line air - Batteries not dead What stops an S stock moving? On something like a 95 or 96 stock the only thing would be load-shedding, and there's a solution to that. In this scenario nothing, the middle cars would easily give enough traction to move the train. But it's one of those worst case scenarios where you have a perfect storm of everything seemingly to go wrong at the same time. This is what I initially meant, the driving cars off current *shouldn't* be a major problem, as long as everyone's on the case promptly. Certainly there have been 95 stocks in this situation for 15-20 minutes and still been able to be quite happily got moving again. The common problem is that the load-shedding leads everyone (both driver and control staff) down the proverbial garden path by throwing up things that are consequence not cause of the real problem, and quite often the driver wasting air by responding to the OPO alarm every minute (ironically TBTC has largely taken away that problem!). |
|
Colin
Advisor
My preserved fire engine!
Posts: 11,346
|
Post by Colin on Dec 24, 2019 18:30:32 GMT
and quite often the driver wasting air by responding to the OPO alarm every minute (ironically TBTC has largely taken away that problem!). Yet S stock adds a layer of complication with CBTC as to save air when acknowledging the OPO alarm whilst in protected manual mode one has to place the traction brake controller into the emergency position.......and guess what that does to other trains in the vicinity....😲😲😐 |
|
North End
Beneath Newington Causeway
Posts: 1,769
|
Post by North End on Dec 24, 2019 18:48:53 GMT
and quite often the driver wasting air by responding to the OPO alarm every minute (ironically TBTC has largely taken away that problem!). Yet S stock adds a layer of complication with CBTC as to save air when acknowledging the OPO alarm whilst in protected manual mode one has to place the traction brake controller into the emergency position.......and guess what that does to other trains in the vicinity....😲😲😐 Can only speak for TBTC, however on the Jubilee and Northern placing the T/BC in emergency doesn't cause an auto MRR to be generated. Placing the MCS <<footnote>> in RM *will*, however. Is it not possible to put the MCS into Auto on an S stock to get round the OPO alarm? On 95 stock there's also a button which can be used to respond to the OPO alarm, which doesn't have the same effect as restroking the T/BC. I take it S stock doesn't have this? <<Rincew1nd: MCS - Master Control Switch>> |
|
Colin
Advisor
My preserved fire engine!
Posts: 11,346
|
Post by Colin on Dec 24, 2019 22:55:36 GMT
That’s correct; S stock doesn’t have such a button.
Putting the master control switch to auto would get rid of the opo alarm but as you allude to above, would a train operator think of that whilst dealing with whatever else might be going on?
|
|
|
|
Post by brigham on Dec 27, 2019 8:33:12 GMT
So, back to the earlier point; the compressors don't work off the traction bus cables, because there ARE no traction bus cables.
It might be an idea, on new builds at least, to provide a 400v supply from an intermediate car also. The chances of three cars being gapped is fairly unlikely.
|
|
|
|
Post by tjw on Dec 27, 2019 8:55:36 GMT
So, back to the earlier point; the compressors don't work off the traction bus cables, because there ARE no traction bus cables. It might be an idea, on new builds at least, to provide a 400v supply from an intermediate car also. The chances of three cars being gapped is fairly unlikely. The problem with traction bus cables is the interconnections between cars. It is all very well for us to sit at computers thinking they are a good idea, but 1. Someone needs to connect and disconnect them. 2. This need to be done safely (Note all the warnings and regulations about leads in depots...) 3. How many EMUs on the southern caught fire because of arcing on Traction bus cables? 4. who is going to clean the connections to prevent deposits building up leading to arcing? |
|
|
|
Post by piccboy on Dec 27, 2019 13:56:08 GMT
So, back to the earlier point; the compressors don't work off the traction bus cables, because there ARE no traction bus cables. It might be an idea, on new builds at least, to provide a 400v supply from an intermediate car also. The chances of three cars being gapped is fairly unlikely. The problem with traction bus cables is the interconnections between cars. It is all very well for us to sit at computers thinking they are a good idea, but 1. Someone needs to connect and disconnect them. 2. This need to be done safely (Note all the warnings and regulations about leads in depots...) 3. How many EMUs on the southern caught fire because of arcing on Traction bus cables? 4. who is going to clean the connections to prevent deposits building up leading to arcing? Automate it on the train. Have the train determine if the leading cars have both gapped and the train is stationary. If so the feeds would be energised. As soon as the train moves or leading cars detect traction current then the link is de-energised. |
|
vato
Zone 6D - Special Fares Apply
Posts: 131
|
Post by vato on Dec 27, 2019 15:18:05 GMT
Sadly, none of that addresses the 4 points you were replying to.
|
|
|
|
Post by zbang on Dec 27, 2019 16:16:31 GMT
The problem with traction bus cables is the interconnections between cars. It is all very well for us to sit at computers thinking they are a good idea, but [...]
All of those can be dealt-with readily, however isn't passing traction current car-to-car they still generally prohibited? (Connor mentions this.)
|
|
|
|
Post by underover on Dec 27, 2019 21:31:34 GMT
The problem with traction bus cables is the interconnections between cars. It is all very well for us to sit at computers thinking they are a good idea, but [...]
All of those can be dealt-with readily, however isn't passing traction current car-to-car they still generally prohibited? (Connor mentions this.)
Generally yes, cars which are designed to uncouple easily (auto couplers), no high voltage passing allowed. You can however pass juice (high voltage) via jumper cable which is generally on semi perms |
|
rincew1nd
Administrator
Junior Under-wizzard of quiz
Posts: 10,286
|
Post by rincew1nd on Dec 28, 2019 7:33:53 GMT
The problem with traction bus cables is the interconnections between cars. It is all very well for us to sit at computers thinking they are a good idea, but [...] All of those can be dealt-with readily, however isn't passing traction current car-to-car they still generally prohibited? (Connor mentions this.)
Not sure about LU, but certainly the National Network seems to gain approval for this on the latest generations of multiple units. AIUI the high tension line runs along the roof. |
|
|
|
Post by brigham on Dec 28, 2019 8:28:19 GMT
There's no need to have a traction bus cable to solve this problem; just a compressor voltage bus, with an intermediate feed.
Perhaps that, too is prohibited?
|
|
