Central line - shortage of serviceable trains

Dstock7080 · 7 Feb 2024

A trial is shortly to start with up to two 8-car trains having the middle traction package isolated via the Traction Control Cut-Out Switch TCCOS.
The trains will operate on the Hainault-Woodford shuttle only.

RailUK Forums

rebmcr · 7 Feb 2024

Dstock7080 said:
A trial is shortly to start with up to two 8-car trains having the middle traction package isolated via the Traction Control Cut-Out Switch TCCOS.
The trains will operate on the Hainault-Woodford shuttle only.

"The middle traction package" doesn't make sense when referring to eight-car 92TS formations.

Is that meant to refer to 'both middle packages', or 'one of the two middle packages', or some other arrangement?

Dstock7080 · 7 Feb 2024

one of four

Nym · 7 Feb 2024

So on the shuttle where you could just operate a four car train anyway, they're going to pull some broken units out to make it look like they're trying.

One has to wonder who thought this was a good idea to appease the political will...

Unless of course it's a performance trial for more widespread use of failed sets with TCCOS operated.

xtmw · 7 Feb 2024

You can't operate a 4 car 92 stock on the shuttle service. This was tried and it kept gapping.

Zeremony · 7 Feb 2024

From an Evening Standard article

Statement from Andy Lord (TfL commissioner):
- 26 out of 31 days in December were affected by stock shortages (including Xmas day)
- An emergency timetable will be introduced within the next four weeks to try to regulate the gaps between trains
- TfL thinks the service will improve by the end of February
- Delays are most common east of Leytonstone

Extra buses have been introduced on the eastern end of the line:
- A bus service from Epping to Chingford via Loughton for the London Overground has been introduced from today
- Extra buses on the 20 route between Debden and Walthamstow Central via Loughton, Buckhurst Hill, Woodford Green & Whipps Cross
- Extra buses on the 150 route between Hainault and Ilford via Fairlop, Barkingside & Gants Hill (not continuing to Becontree Heath)

Nym · 7 Feb 2024

xtmw said:
You can't operate a 4 car 92 stock on the shuttle service. This was tried and it kept gapping.

"Professional Driving Techniques"
or
"Close the gaps!"

Zeremony · 7 Feb 2024

Regarding extra buses on the 150/20:

Two buses were allocated from Palmers Green garage to run on the 150 route today.
Also two extra buses for the 20 are meant to be running

All additional buses won't show up on iBus (you won't be able to track them) as they are additional buses not in the timetable

Might relive some pressure as people opt for using Elizabeth line to Ilford for the 150, and Overground/Victoria line to Walthamstow for the 20

Central · 7 Feb 2024

Surely a train running all day with 3 traction packages instead of 4 will put more strain on the three that are working causing more motor problems.

trebor79 · 8 Feb 2024

Central said:
Surely a train running all day with 3 traction packages instead of 4 will put more strain on the three that are working causing more motor problems.

Not really I wouldn't have thought. If a motor is being run within specification it won't cause an issue regardless of whether it's at 99% or 80% of rated current.

D7666 · 8 Feb 2024

xtmw said:
You can't operate a 4 car 92 stock on the shuttle service. This was tried and it kept gapping.

Indeed, and fixing those gaps, even if that were a way forward, is not simple, not simply splicing in a few extra metre of conductor rail, the site specifics are complex.

trebor79 said:
Not really I wouldn't have thought. If a motor is being run within specification it won't cause an issue regardless of whether it's at 99% or 80% of rated current.

Which overlooks the whole point that the motors are totally clapped out and life expired.

If you knock out 1/4 of a trains power capability i.e. one 2car set, to maintain 100% performance each of what is left have to run at 33% overload compared to normal. On clapped out kit ? Even if that overload is within spec, all that will happen is accelerate the decline of what is working.

Central said:
Surely a train running all day with 3 traction packages instead of 4 will put more strain on the three that are working causing more motor problems.

correct

trebor79 · 8 Feb 2024

trebor79 said:
Not really I wouldn't have thought. If a motor is being run within specification it won't cause an issue regardless of whether it's at 99% or 80% of rated current.

D7666 said:
Which overlooks the whole point that the motors are totally clapped out and life expired.

If you knock out 1/4 of a trains power capability i.e. one 2car set, to maintain 100% performance each of what is left have to run at 33% overload compared to normal. On clapped out kit ? Even if that overload is within spec, all that will happen is accelerate the decline of what is working.

No, it really doesn't work like that with electric motors. The power electronics will be configured so that they cannot run in an "overload" situation. Running a motor at 10% FLC doesn't wear it out any less quickly than running at 99% FLC, provided the cooling arrangements etc are working properly.

D7666 · 8 Feb 2024

trebor79 said:
No, it really doesn't work like that with electric motors. The power electronics will be configured so that they cannot run in an "overload" situation. Running a motor at 10% FLC doesn't wear it out any less quickly than running at 99% FLC, provided the cooling arrangements etc are working properly.

If you say so. I only worked on the Central for over 10 years so what do I know about it.

The DC motors on 92TS are each 46 kW cont 54 kW one hour rating. That gives you 1472 kW cont / 1728 kW one hour for an 8car train. But a 8car 92TS accelerating draws (I think) 3000 A, which at 630 V line = 1890 kW. A (small) proportion of that load is taken by train auxiliaries, but leaves, say, 1800 kW for traction. 1800 kW is way over the 1472 kW rating, and over the 1728 kW one hour rating, even allowing for the default 9% losses in DC motors. These are DC traction motors, and series wound DC railway traction motors always work in overload zone during acceleration. Full stop. That is how DC motor electric trains work in practice.

Further, arguing that running at 10% underload vice 99% is not the point of debate - what is the point is running at 33% overload vice 100%. Even if you have perfect cooling, your commutator and brushes wear increases, more stress on bearings, and so on. Worn bearing => vibration => impaired commutation, increases degradation.

Or. If you insist, I'll point out that to maintain timetable, 92TS runs flat out, into the overload zone on the performance curve, full motoring then flat out full braking (motors do the bulk braking effort) and if can not overload, to run 8car train with one 2car cut out => 25% traction AND 25% BRAKING effort cut out - you can not maintain point to point run times; ok you only lose a few seconds each run, but on every point to point, which accumulates, and then also this with more than one train (as that is the logical extension of what is suggested) the timetable collapses; the ATO timetable has a resolution of 1 second***, and trains behind the cut out one will start to block back. All day.

So.

EITHER you can't run the timetable with cut out cars (if motors are load capped) or will damage the remaining motors (if motors are not load capped).

Either way. You don't do it. Which is why we don't.

*** a little of which I did some calculations for a mod last decade

notverydeep · 8 Feb 2024

D7666 said:
Indeed, and fixing those gaps, even if that were a way forward, is not simple, not simply splicing in a few extra metre of conductor rail, the site specifics are complex.

The current rail gaps causing issues were in Hainault depot rather than on the Hainault to Woodford run itself, and the main mitigation was going to be to avoid those depot routes where possible, with instructions to stop where the 4 car trains wouldn't get gapped. Thus it wasn't this that prevented 4 car operation. The main reason that the 4 car initiative foundered was that without returning 91337 and 91341 to service, the cab cars that would enable another 8 car to be made up from the freed up vehicles were not going to be available - and without that released 8 useable car train to cover for a unit in the CLIP programme, 4 car operation didn't help the maintainers much since it only released non-cab B-C or B-D units. The project to revive 91341 came to a halt at the beginning of the pandemic and has not (so far) been re-started...

rebmcr · 8 Feb 2024

D7666 said:
Or. If you insist, I'll point out that to maintain timetable, 92TS runs flat out, into the overload zone on the performance curve, full motoring then flat out full braking (motors do the bulk braking effort) and if can not overload, to run 8car train with one 2car cut out => 25% traction AND 25% BRAKING effort cut out - you can not maintain point to point run times; ok you only lose a few seconds each run, but on every point to point, which accumulates, and then also this with more than one train (as that is the logical extension of what is suggested) the timetable collapses; the ATO timetable has a resolution of 1 second***, and trains behind the cut out one will start to block back. All day.

So.

EITHER you can't run the timetable with cut out cars (if motors are load capped) or will damage the remaining motors (if motors are not load capped).

Or, you put a 3/4 train on the Hainault loop, to find out what it is capable of without burning out, and then use that knowledge to write an interim timetable to match that performance.

D7666 · 8 Feb 2024

rebmcr said:
Or, you put a 3/4 train on the Hainault loop, to find out what it is capable of without burning out, and then use that knowledge to write an interim timetable to match that performance.

strangely enough LU does have computer simulations and timetable compilers to do that sort of thing

we do not need to go break a train to find that what we already know don't work as a solution won't work as a solution

notverydeep said:
The current rail gaps causing issues were in Hainault depot rather than on the Hainault to Woodford run itself, and the main mitigation was going to be to avoid those depot routes where possible, with instructions to stop where the 4 car trains wouldn't get gapped. Thus it wasn't this that prevented 4 car operation. The main reason that the 4 car initiative foundered was that without returning 91337 and 91341 to service, the cab cars that would enable another 8 car to be made up from the freed up vehicles were not going to be available - and without that released 8 useable car train to cover for a unit in the CLIP programme, 4 car operation didn't help the maintainers much since it only released non-cab B-C or B-D units. The project to revive 91341 came to a halt at the beginning of the pandemic and has not (so far) been re-started...

all that is precisely why I said "even if that were a way forward, is not simple"; the keyword there is 'if' ; I was unware of how much was in the public domain so was not going into the details, merely making a general comment about gaps and why as I also Said "the site specifics are complex." which I knew was in depot not easy to alter but not wanting to go into details if not in public domain

boiledbeans2 · 8 Feb 2024

D7666 said:
If you say so. I only worked on the Central for over 10 years so what do I know about it.

The DC motors on 92TS are each 46 kW cont 54 kW one hour rating. That gives you 1472 kW cont / 1728 kW one hour for an 8car train. But a 8car 92TS accelerating draws (I think) 3000 A, which at 630 V line = 1890 kW. A (small) proportion of that load is taken by train auxiliaries, but leaves, say, 1800 kW for traction. 1800 kW is way over the 1472 kW rating, and over the 1728 kW one hour rating, even allowing for the default 9% losses in DC motors. These are DC traction motors, and series wound DC railway traction motors always work in overload zone during acceleration. Full stop. That is how DC motor electric trains work in practice.

In general, I agree with your points that a motor pushed harder, even within ratings, is going to wear out faster.

However, the 1992 stock doesn't use series wound DC motors. They use separately excited DC motors, which was made possible by the introduction of power electronics - the GTO thyristor - to separately control the field and armature voltage.

Therefore, there is no additional "overload zone" as you imply, where the motor works beyond the peak 54 kW power or peak torque.

trebor79 · 8 Feb 2024

Well, it appears LU are doing exactly what @D7666 says is going to break more motors. So either they know it's not likely that will be the outcome, or the risk reward is worth it.
I suppose if the unit was stopped anyway for lack of spares, you might as well run it (and therefore release another fully working order train for the rest of the line) to failure and fix it when the next batch of motors arrives.

D7666 · 8 Feb 2024

boiledbeans2 said:
However, the 1992 stock doesn't use series wound DC motors. They use separately excited DC motors, which was made possible by the introduction of power electronics - the GTO thyristor - to separately control the field and armature voltage.

Therefore, there is no additional "overload zone" as you imply, where the motor works beyond the peak 54 kW power or peak torque.

ok ............. I get it if they are separate excitation ........... that caps things at a lower limit than I stated ....

but .......

even then, 54 kW per motor is still an overload, 17% actually (54/46) and the trains need to use this to maintain timetable

So while the detail of what I posted was flawed, the underlying principle is correct.

If you then run a train with 1/4 of those motors cut out, you either can not maintain timetable (if really capped at that value) or further stress things (if not capped at that value)

And all this leads to the same answer = why we do not do it.

And none of it addresses that the motors are clapped out and probably at BER. Which is why we at this sad point in 92TS history.

Central · 8 Feb 2024

If a traction package is cut out won’t the regen brake fail to work and the train will be using friction braking all the time.This happened on rheostatic brake stock.On the Victoria Line this resulted in less precise
station braking with stopping short incidents.

D7666 · 8 Feb 2024

Central said:
If a traction package is cut out won’t the regen brake fail to work and the train will be using friction braking all the time.This happened on rheostatic brake stock.On the Victoria Line this resulted in less precise
station braking with stopping short incidents.

There was something like that at the back of my mind too. One of the things I'd need to go away and consult manuals for.

I did allude to this upthread when I wrote 25% loss brake effort - meaning dynamic braking.

Dstock7080 said:
one of four

I'm not saying any more than if they are doing this, there is more to it than meets the eye i.e. it is more work than simply cutting out one 2car unit.

bramling · 8 Feb 2024

Central said:
If a traction package is cut out won’t the regen brake fail to work and the train will be using friction braking all the time.This happened on rheostatic brake stock.On the Victoria Line this resulted in less precise
station braking with stopping short incidents.

This happened on the Northern when the dynamic braking was isolated on the middle motor cars (*). This resulted in some slight deterioration in braking performance, a considerable increase in reports of burning smells, and no doubt an increase in brake block wear. For Hainault to Woodford this probably shouldn’t be an issue however.

(* done as part of a trial IIRC to try and reduce glazing on brake blocks, think it was selected trains rather than the whole fleet but I can’t remember the specifics).

I think they would probably get away with having two cars worth of motors isolated on an 8-car train doing Hainault to Woodford shuttles, however one presumes there might have to be some other measures like reducing the amount of motoring demanded, or perhaps reducing the top speed. I tend to agree with the view that it isn’t really desirable, but the whole situation seems to have got somewhat desperate so I guess anything is worth a try. This does more smack of being seen to be doing something rather than a magic bullet though.

xtmw · 9 Feb 2024

Could be worth Wood Lane turning on the autumn brake rate (which results in softer braking) between Hainault and Roding Valley during this trial. The top speed ATO can do on the Hainault shuttle is 85kmh.

D7666 · 10 Feb 2024

If the issue is with motors themselves, have often wondered if Sandite is a cause. Could get drawn in. You really do not want any of that in a commutator. Even a tiny bit is damaging if it gets in there somehow. Failures out of phase with sandite season : accumulative fault, so lags i.e. sandite ~ 0ctober to December, does the damage but takes time to develop into faults => December onwards peaking in cold weather but not necessarily a result of it. 92TS motor issues are known to be seasonal, this year is not new in that respect.

boiledbeans2 · 15 Feb 2024

The poor Central Line service was on the 6.30pm BBC1 News yesterday.

Questions were asked about whether the fare freeze by the Mayor has led to a lack of money for TfL, and therefore the poor Central Line service.

Watch from the start here:

BBC London - Evening News: 14/02/2024

The latest news, sport and weather from London.

www.bbc.co.uk

Mawkie · 15 Feb 2024

boiledbeans2 said:
The poor Central Line service was on the 6.30pm BBC1 News yesterday.

Questions were asked about whether the fare freeze by the Mayor has led to a lack of money for TfL, and therefore the poor Central Line service.

The BBC are so sensationalist these days. At least Tom Edwards seems fair in most of his reports. It's quite right the Transport Editor deals with transport related items. Nearly everyone I know cries out to take the politics out of transport, but when the BBC then wheels out it's Political Editor at every opportunity, its quite hard to do.

Dstock7080 · 17 Feb 2024

TTN99/24:
21tph through the core White City-Leytonstone Mon-Thu.
Night Tube and weekends unchanged

0700-2300 Mon-Thu
services:
West Ruislip-Epping 9tph
Ealing Broadway-Hainault via Newbury Park 6tph
White City-Hainault via Newbury Park 6tph
frequency:
West Ruislip-North Acton 6¼-7mins
Ealing Broadway-North Acton 9-11mins
North Acton-White City 3-5½mins
White City-Leytonstone 2¾–3mins
Leytonstone-Hainault 3¼-5¾mins
Leytonstone-Woodford 6-8mins
Woodford-Epping 6-8mins
Woodford-Hainault 20mins

Normal provision for 60 train service but contingency for 58, 56, 53 train availability, with planned cancellations.

Snow1964 · 17 Feb 2024

Dstock7080 said:
Normal provision for 60 train service but contingency for 58, 56, 53 train availability, with planned cancellations.

Not a very good ratio vs full fleet of 85 trains
60 trains is 70.6% usage
53 trains is 62.3% usage

Can't think of any other electric train fleets where timetable 3 spare trains for every 7 in service at busiest time. Highlights the seriousness of inadequate equipment

Busman · 19 Feb 2024

I assume that means there are two trains working the Hainault branch again?

Dstock7080 · 19 Feb 2024

Indeed T171 T172

Central line - shortage of serviceable trains

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