Do new trains give too much power?

[O L Leigh]

In the past week or so there have been two suggestions that new classes of traction have excess power which makes it difficult to drive them smoothly. Over on GA, it seems that the Stadlers always want to accelerate even in low power settings and require the use of speed set to keep them reined-in, while over in the west there are reports that IETs give a jolty ride when driven slowly. While it can be nice to have a train that can get down the road at a decent lick, I'm starting to wonder if this turn of events is necessarily a good one.

To give some background, when I learned 1980s era BR EMUs there were four power notches. These basically were "Shunt" which gave you no more than about 5mph, "Half Power" which would get a 100mph EMU up to about 50mph, "Full Power" which would get you all the way up to top speed, and "Weak Field" which would get you there that little bit faster. Each power notch gave progressively more power for acceleration. Driving them was quite a simple affair as a result. It was notch 1 in depots and sidings, notch 4 to get away from stations/signals and notch 2 generally for holding speed at around 80mph depending on gradient, etc.

When the Cl379 Electrostar units were introduced the driver instructors noticed that, while notch 1 still gave very low power, the train would continue to accelerate past 5mph. As an experiment, they decided to leave the unit in notch 1 and see what speed it would get to. While I don't recall the precise details, the train did reach an appreciable percentage of it's maximum speed before a signal check called a halt to proceedings. However, driving the trains in service was very little different to their older forebears. You just had to remember not to leave it in notch 1 if you were on the shed with it.

While I have no doubt that my colleagues up in the pointy ends of Stadlers and IETs will have adjusted to a greater or lesser extent to their new steeds, and that new drivers will know nothing different, I do wonder if an argument exists for remapping the power controllers so as not to give quite so much power at low inputs so that trains can be driven more smoothly and to return some of the control to the driver rather than the driver needing to employ the computer just to control the train speed.

Thoughts...?

 

[trebor79]

Not a driver, but as a paying punter the Stadlers are far smoother and less jolty than the Cl90+Mk3 sets. There was always a BANG and jolt setting off from Liverpool street as the 90 pushed the couplings slack from the back, and you knew where the speed limits changed as there was a jolt with every application or reduction of power.
The Stadlers just accelerates and decelerate quickly, but smoothly. No more jolting.

 

[Bletchleyite]

Not a driver, but as a paying punter the Stadlers are far smoother and less jolty than the Cl90+Mk3 sets. There was always a BANG and jolt setting off from Liverpool street as the 90 pushed the couplings slack from the back, and you knew where the speed limits changed as there was a jolt with every application or reduction of power.
The Stadlers just accelerates and decelerate quickly, but smoothly. No more jolting.

That was always noticeable on the WCML too - you'd always start with BANG-judder-judder-judder because of the semi-rigid couplings, and often another shock wave or two when accelerating or decelerating when moving. You never got it in mainland Europe where the buffers allowed a bit more movement. I've not noticed it on 91+Mk4 though.

Yes, the software should perhaps bring the power in more gradually so as to avoid harsh starts? Would be handy on buses too, as these often seem to have a binary throttle.

With regard to shunting, it would seem to make more sense rather than a notch to have a shunt mode that limited speed to 5mph regardless of what you did with the handle? I very much like my car's manual speed limiter, I use it all the time in lower limits, allowing me to avoid watching the speedo and concentrate on the road without any risk of speeding.

 

[43096]

That was always noticeable on the WCML too - you'd always start with BANG-judder-judder-judder because of the semi-rigid couplings, and often another shock wave or two when accelerating or decelerating when moving. You never got it in mainland Europe where the buffers allowed a bit more movement. I've not noticed it on 91+Mk4 though.

It’s down to the different couplers. West Coast sets were buckeye coupled between vehicles (and screw coupled between stock and loco if an 86 or 87). The Mark 4 sets are Tightlock between vehicles (similar to BR EMUs between sets) with a buckeye between the TOE and the 91. 91s are notoriously slow off the mark, though, which will further reduce coupler snatching.

 

[_toommm_]

That was always noticeable on the WCML too - you'd always start with BANG-judder-judder-judder because of the semi-rigid couplings, and often another shock wave or two when accelerating or decelerating when moving. You never got it in mainland Europe where the buffers allowed a bit more movement. I've not noticed it on 91+Mk4 though.

Yes, the software should perhaps bring the power in more gradually so as to avoid harsh starts? Would be handy on buses too, as these often seem to have a binary throttle.

With regard to shunting, it would seem to make more sense rather than a notch to have a shunt mode that limited speed to 5mph regardless of what you did with the handle? I very much like my car's manual speed limiter, I use it all the time in lower limits, allowing me to avoid watching the speedo and concentrate on the road without any risk of speeding.

I believe some units have a wash button which limits it to 3 or 5 mph, and some 37s have slow speed control to hold the train at 0.5, 1.0, or 2.7 mph. Whilst I’ve only seen the latter in Train Simulator, the creators of the pack do lots of research, so I’ll happily concur with them that certain 37s had them:

https://www.armstrongpowerhouse.com/free_download/manuals/APC37V1_Manual.pdf#page34

 

[ac6000cw]

To give some background, when I learned 1980s era BR EMUs there were four power notches. These basically were "Shunt" which gave you no more than about 5mph, "Half Power" which would get a 100mph EMU up to about 50mph, "Full Power" which would get you all the way up to top speed, and "Weak Field" which would get you there that little bit faster. Each power notch gave progressively more power for acceleration.

Over on GA, it seems that the Stadlers always want to accelerate even in low power settings and require the use of speed set to keep them reined-in, while over in the west there are reports that IETs give a jolty ride when driven slowly.

When the Cl379 Electrostar units were introduced the driver instructors noticed that, while notch 1 still gave very low power, the train would continue to accelerate past 5mph. As an experiment, they decided to leave the unit in notch 1 and see what speed it would get to. While I don't recall the precise details, the train did reach an appreciable percentage of it's maximum speed before a signal check called a halt to proceedings.

Not a driver (I'm an electronics engineer), but I wonder if the notches on the old BR EMUs effectively set the voltage to the (DC) traction motors, which would mean that in the Shunt and Half Power notches the speed would stop increasing once the motor back-EMF got close to the voltage. So they were effectively speed-limited notches.

In contrast the "Over on GA, it seems that the Stadlers always want to accelerate even in low power settings" and "When the Cl379 Electrostar units were introduced the driver instructors noticed that, while notch 1 still gave very low power, the train would continue to accelerate past 5mph" situation suggests the power control setting (on these modern AC-traction drive units) behaves more like a 'tractive effort' controller - so the train only stops accelerating when the rolling resistance/effect of gradients/wind resistance matches the set tractive effort?

(But this is just some theoretical musings...)

 

[O L Leigh]

Not a driver, but as a paying punter the Stadlers are far smoother and less jolty than the Cl90+Mk3 sets. There was always a BANG and jolt setting off from Liverpool street as the 90 pushed the couplings slack from the back, and you knew where the speed limits changed as there was a jolt with every application or reduction of power.
The Stadlers just accelerates and decelerate quickly, but smoothly. No more jolting.

That was always noticeable on the WCML too - you'd always start with BANG-judder-judder-judder because of the semi-rigid couplings, and often another shock wave or two when accelerating or decelerating when moving. You never got it in mainland Europe where the buffers allowed a bit more movement. I've not noticed it on 91+Mk4 though.

The banging and crashing that was characteristic of push-pull working on the West Coast and Anglia is a separate issue related to the rolling stock. It could be mitigated by the driver but never in my experience could it ever be completely eradicated.

To me, it just highlighted how little thought had gone into this method of working and how it would be implemented. The Mk4 stock, which was designed from the outset for push-pull operation, were equipped with Tightlock couplers, which is something I think should have been considered for the Mk2 and Mk3 stock also. That an MU can waft out of a station without the percussive accompaniment should hardly be a surprise.

With regard to shunting, it would seem to make more sense rather than a notch to have a shunt mode that limited speed to 5mph regardless of what you did with the handle? I very much like my car's manual speed limiter, I use it all the time in lower limits, allowing me to avoid watching the speedo and concentrate on the road without any risk of speeding.

I believe some units have a wash button which limits it to 3 or 5 mph

Indeed. But shunting isn't the root of my concern, as the car wash button isn't going to be any use to a driver out on the mainline who is looking to control the speed of the train for him/herself.

 

[ac6000cw]

Not a driver, but as a paying punter the Stadlers are far smoother and less jolty than the Cl90+Mk3 sets. There was always a BANG and jolt setting off from Liverpool street as the 90 pushed the couplings slack from the back, and you knew where the speed limits changed as there was a jolt with every application or reduction of power.
The Stadlers just accelerates and decelerate quickly, but smoothly. No more jolting.

I agree with that - and the 3-car 755s on OHLE power are very quick off the mark, with 3500hp for probably around 140t unit weight (25hp/tonne!)

 

[100andthirty]

Freight train drivers have to be very aware of the bang-jolt effect when accelerating and braking. A good driver will set off using very little acceleration to take up the slack in the couplings and a very light initial brake application to make sure all the buffers are in compression. If this is not done there could be broken couplings (too much acceleration) or locked buffers/derailments (braking), certainly in countries where very long freight trains are operated.

Modern passenger trains with auto couplers between units and bar couplers between cars don't fortunately suffer this effect. The full power of the trains can't actually be delivered at zero speed, only the maximum tractive effort that is determined by the low speed torque of the motors, the number of powered axles and the adhesion. The software should seek to control the acceleration rate, and apply jerk control which in engineering terms is expressed as the rate of change of the acceleration rate. So if the train is designed to accelerate at 1.0 metres per second per second, I would expect a ramp up from zero to the full acceleration rate over 1.0 to 1.5 seconds. Jerk control is usually applicable when acceleration and braking is applied or released. The only time it can't work is when the train comes brakes to a stop. This requires the driver to ease off the brake for a smooth stop. On my line the drivers are very good at it. On metros with ATO a smooth stop is attempted but because of the accurate stop required there is often a (hopefully) small jerk.

If the supplier has got the jerk control wrong this is what can lead to jerks. If the driver (or ATO) doesn't accommodate the jerk control, then there can be lurching (accelerate on-off-on-off) something that can be experienced on some partd of the LU Northern or Jubilee lines.

 

[gingerheid]

The GA Stadlers are amazing. My only request is for all trains in the UK to be replaced with them. After a sleeper I'd rather go from London to Scotland in even a 755 than anything that's actually running the journey! I was on a 745 yesterday and yeah, I get that it's got less character than the previous loco hauled stuff. But... that is what I want the future to look like.

 

[bramling]

In the past week or so there have been two suggestions that new classes of traction have excess power which makes it difficult to drive them smoothly. Over on GA, it seems that the Stadlers always want to accelerate even in low power settings and require the use of speed set to keep them reined-in, while over in the west there are reports that IETs give a jolty ride when driven slowly. While it can be nice to have a train that can get down the road at a decent lick, I'm starting to wonder if this turn of events is necessarily a good one.

To give some background, when I learned 1980s era BR EMUs there were four power notches. These basically were "Shunt" which gave you no more than about 5mph, "Half Power" which would get a 100mph EMU up to about 50mph, "Full Power" which would get you all the way up to top speed, and "Weak Field" which would get you there that little bit faster. Each power notch gave progressively more power for acceleration. Driving them was quite a simple affair as a result. It was notch 1 in depots and sidings, notch 4 to get away from stations/signals and notch 2 generally for holding speed at around 80mph depending on gradient, etc.

When the Cl379 Electrostar units were introduced the driver instructors noticed that, while notch 1 still gave very low power, the train would continue to accelerate past 5mph. As an experiment, they decided to leave the unit in notch 1 and see what speed it would get to. While I don't recall the precise details, the train did reach an appreciable percentage of it's maximum speed before a signal check called a halt to proceedings. However, driving the trains in service was very little different to their older forebears. You just had to remember not to leave it in notch 1 if you were on the shed with it.

While I have no doubt that my colleagues up in the pointy ends of Stadlers and IETs will have adjusted to a greater or lesser extent to their new steeds, and that new drivers will know nothing different, I do wonder if an argument exists for remapping the power controllers so as not to give quite so much power at low inputs so that trains can be driven more smoothly and to return some of the control to the driver rather than the driver needing to employ the computer just to control the train speed.

Thoughts...?

The answer may well be yes. The ideal would seem to be enough power to reach line speed when required, plus a bit more to give good acceleration when on stopping services.

Even if one takes something like LU, a metro application where power is generally good, something like the Northern Line is constant on/off motoring as the train reaches the speed profile that little bit too readily, and these trains are a generation less powerful than what would be provided if being built now. This isn’t good for the driver, and it’s not great for the passenger either. Likewise whilst modern AC traction packages don’t seem to mind being abused in this way, it still seems to put stress on other aspects of the train.

 

[notadriver]

I think all modern trains should have an adjustable speed limiter (which stadler units have) but many such as 195s and 331s don’t which would help give a smoother ride at line speeds across the whole speed range.

Does anyone know if 80x have had their acceleration rates so they don’t cause passengers to fall over if the driver selects full power from a standing start ?

 

[whoosh]

On class 700s, you can select half power from a stand with the power controller, but by the time you are upto about 40mph on AC, or 25mph on DC, it's actually giving full power.
Whilst it says 'power' next to the power controller, on the display screen is a bar graph labelled 'Tractive Effort'.
It's more like a tractive effort selector - you need lots of tractive effort from a stand to get going, but not as much at high speed. Only 5% to 10% on the graph is what is actually giving you full power at 90 - 100mph. Any power controller movement past that point at that speed, isn't actually doing anything.

So basically, the higher your speed, the less movement of the power controller from the 'off' position is needed to give you full power. But they don't tell you that on the training course, and some drivers still haven't got the hang of it, not realising that at high speeds, minute movements of the controller (away from the off position) make large adjustments in power. Until full power is reached, and then the rest of the travel of the lever is redundant.

It's totally different to any other train that's gone before it, and hasn't been explained properly - compounded by possible mislabelling of the 'power' controller. If you move the 'power' controller to the half way position when your doing 60mph for example. You don't get half power. You get full power. The screen labelled 'tractive effort' shows an arrow at 50% which is what you've selected, but the bar on the bar graph doesn't go as far as the arrow - maybe 20%. But you've got full power!

Full power is the position of the power controller at the point the tractive effort bar on the bar graph dips below the arrow.

So going back to starting off on half power, the tractive effort bar will be level with the 50% selected but power will be increased as the train gains speed, until the tractive effort falls away below 50%. At this point, with the lever half way, you're getting full power.

I'll take a guess and wager that the Stadlers are similar.

 

[43066]

I think all modern trains should have an adjustable speed limiter (which stadler units have) but many such as 195s and 331s don’t which would help give a smoother ride at line speeds across the whole speed range.

Does anyone know if 80x have had their acceleration rates so they don’t cause passengers to fall over if the driver selects full power from a standing start ?

I’m not quite clear how an adjustable speed limit would give a smoother ride?

 

[XAM2175]

Whilst it says 'power' next to the power controller, on the display screen is a bar graph labelled 'Tractive Effort'.
...
It's totally different to any other train that's gone before it, and hasn't been explained properly - compounded by possible mislabelling of the 'power' controller. ...

That's the standard configuration for trains in Germany for yonks now, IIRC going right back to ABB-Henschel's first solid-state traction package in the late '70s, but yes I can completely imagine it's a big leap conceptually from the previous way of having a handful of physical power notches and especially so without a good explanation in training.

 

[irish_rail]

I think all modern trains should have an adjustable speed limiter (which stadler units have) but many such as 195s and 331s don’t which would help give a smoother ride at line speeds across the whole speed range.

Does anyone know if 80x have had their acceleration rates so they don’t cause passengers to fall over if the driver selects full power from a standing start ?

The 80x are noticeably slower from a standing start than when first introduced for the first few mph, presumably this was done due to the sheer number of passengers falling over whilst loading their luggage having just boarded. I never used full power from the off anyway for this reason and out of sympathy to the inboard hosts! Clearly somebody realised IETs are not metro trains and passengers don't just get on and sit down instantly.

 

[43066]

I never used full power from the off anyway for this reason and out of sympathy to the inboard hosts! Clearly somebody realised IETs are not metro trains and passengers don't just get on and sit down instantly.

I tend to whack it straight into max (non IET stock)! There’s a timetable to keep to .

 

[Roast Veg]

This is nothing a TCMS update couldn't modify these days surely?

 

[TheEdge]

I’m not quite clear how an adjustable speed limit would give a smoother ride?

On the FLIRTs it noticeably does.

On the Sprinters you could hit line speed, put it into notch 2/3 and it would happily maintain speed without too much adjustment, giving a nice smooth ride. I find its very hard with the FLIRTs to give them the tiniest bit of brake or power with the manual controller, mainly due to the way they are sprung to return the controller to centre, they go to straight to 10%ish and they then start accelerating or braking. When they are on their speed set they are much smoother and they use 1/2% of either and are much nicer.

Its noticeable as a passenger if you are on one where the driver is trying to maintain the speed or the speed set.

 

[43066]

On the FLIRTs it noticeably does.

On the Sprinters you could hit line speed, put it into notch 2/3 and it would happily maintain speed without too much adjustment, giving a nice smooth ride. I find its very hard with the FLIRTs to give them the tiniest bit of brake or power with the manual controller, mainly due to the way they are sprung to return the controller to centre, they go to straight to 10%ish and they then start accelerating or braking. When they are on their speed set they are much smoother and they use 1/2% of either and are much nicer.

Its noticeable as a passenger if you are on one where the driver is trying to maintain the speed or the speed set.

Thanks, makes sense.

Thankfully not a unit I have any experience of driving, and neither do I ever hope to!