Is third rail bad at acceleration?

[hkstudent]

I am on a well delayed Class 465 Southeastern train with nothing ahead in signal diagram. I feel that the driver trying to cut time by minimising dwell time as much as possible.

But it appears to me that the train just don’t accelerate fast, as those Class 710 on Overhead lines, which in normal running circumstances, do have the sense of “push back” feeling and train getting to cruising speed in 10 seconds; while Southeastern one would take 45 seconds to achieve that.
It just make taking southeastern metro feeling ages to travel on.

Of course, compare to S stock in London Underground, there is also push back feeling even on those non auto driving section.

Is it the power traction issue, or the rolling stock itself, or just internal driving guidance caused the slower running and longer runtime between stations, especially metro ones? It is even more obvious when comparing Southeastern runtime with Southwestern runtime (faster) and with Great Northern / London Overhround runtime (even faster) on a same distance, same number of stations, simialr curvature conditions.

 

[D6975]

The design of the 465s dates back to 1991. You can't honestly expect such a unit to be anywhere near the performance of brand new units like 710, 720 etc.

 

[hexagon789]

710s are among the fastest accelerating trains in service in the UK, 465s are nevertheless about the fastest on third rail.

However, the difference is quite stark - about 30 secs of a difference in 0-60 times. It wouldn't be as pronounced if they were on the same electric system; it's not really a fair comparison.

 

[CarrotPie]

I am on a well delayed Class 465 Southeastern train with nothing ahead in signal diagram. I feel that the driver trying to cut time by minimising dwell time as much as possible.

But it appears to me that the train just don’t accelerate fast, as those Class 710 on Overhead lines, which in normal running circumstances, do have the sense of “push back” feeling and train getting to cruising speed in 10 seconds; while Southeastern one would take 45 seconds to achieve that.
It just make taking southeastern metro feeling ages to travel on.

Of course, compare to S stock in London Underground, there is also push back feeling even on those non auto driving section.

Is it the power traction issue, or the rolling stock itself, or just internal driving guidance caused the slower running and longer runtime between stations, especially metro ones? It is even more obvious when comparing Southeastern runtime with Southwestern runtime (faster) and with Great Northern / London Overhround runtime (even faster) on a same distance, same number of stations, simialr curvature conditions.

The Class 465s were (and I believe still are) the fastest accelerating juice rail units in the country. A 12-car Electrostar set, on the other hand, is one of the slowest acelerating trains! The main issue with faster acceleration is power supply, which the juice rail just can't deliver.* AC units can accelerate much faster due to the higher power supply compared to the ground-mounted third rail.

*having said that, the Helsinki Metro uses bottom-contact third rail and our CAF units do very much push you back in your seat/through you down the train, despite only having 75% axles motored and still having their acceleration limited.

 

[Skie]

The Class 465s were (and I believe still are) the fastest accelerating juice rail units in the country.

777s and LU stock have taken that title.

 

[edwin_m]

Dual voltage units tend to have worse performance on the third rail because the power is deliberately limited to avoid overloading the supply. I think the 707s were delivered with fewer motors (relative to their length) than the 700s and 717s because they were third rail only and couldn't draw enough current for the extra motors to improve acceleration.

 

[Samzino]

777s and LU stock have taken that title.

777s and lu stock are considered light rail however?

However I always thought that 444s were considered the fastest accelerating units on DC?

 

[MCR247]

777s and lu stock are considered light rail however?

However I always thought that 444s were considered the fastest accelerating units on DC?

I’d have thought 450s would accelerate quicker than 444s as 450s have 2 motor carriages and 2 trailers, whereas 444s have 2 motors and 3 trailers. But I don’t know how they compare to other stock

 

[CarrotPie]

I’d have thought 450s would accelerate quicker than 444s as 450s have 2 motor carriages and 2 trailers, whereas 444s have 2 motors and 3 trailers. But I don’t know how they compare to other stock

444s have a similar traction package to 450s, but they have 8 motored axles for 6* cars, as opposed to 4 cars on a 450.

*5 cars of a 444 = 6 cars of a 450, which I'm adjusting for.

777s and LU stock have taken that title.

LU stock are cheating because they use the double juice rail system.

777s and lu stock are considered light rail however?

LU stock could be (at least metro), but 777 is essentially a souped-up standard NR EMU: they're more heavy rail than metro.

 

[Taunton]

The design of the 465s dates back to 1991. You can't honestly expect such a unit to be anywhere near the performance of brand new units like 710, 720 etc.

There are Underground trains older than that, and just 630v DC, which accelerate (and brake to a stop) faster than anything on the national network. It's nothing to do with 3rd rail.

 

[Samzino]

444s have a similar traction package to 450s, but they have 8 motored axles for 6* cars, as opposed to 4 cars on a 450.

*5 cars of a 444 = 6 cars of a 450, which I'm adjusting for.

LU stock are cheating because they use the double juice rail system.

LU stock could be (at least metro), but 777 is essentially a souped-up standard NR EMU: they're more heavy rail than metro.

Ah fairs yes, 777s I forget replaced the older 502s

There are Underground trains older than that, and just 630v DC, which accelerate (and brake to a stop) faster than anything on the national network. It's nothing to do with 3rd rail.

Indeed but are much lighter, lower profiled and geared to 40mph or 50 which is considerably helpful when accelerating.

 

[CarrotPie]

There are Underground trains older than that, and just 630v DC, which accelerate (and brake to a stop) faster than anything on the national network. It's nothing to do with 3rd rail.

It is partly to do with third rail, which isn't as good as OLE for supplying power to trains. However, metro systems have it in their best interests to soup up their motors and power supply systems to enable their trains to accelerate much faster, whether on juice rail or OLE. If you had metro-style souped up OLE and some similarly high-performance metro trains, they would accelerate quicker.

 

[AM9]

444s have a similar traction package to 450s, but they have 8 motored axles for 6* cars, as opposed to 4 cars on a 450.

*5 cars of a 444 = 6 cars of a 450, which I'm adjusting for.

I think that the class 444's software limits the maximum current draw less than the class 450's, thereby giving them all a similar power to weight ratio. ISTR that the figures were 67% full power vs 50% respectively. That gives them compatible performance when running to tight headways.

 

[reddragon]

A simple solution available today is to install batteries to supplement the limited 3rd rail supply. This would enable higher acceleration rates.

 

[Samzino]

A simple solution available today is to install batteries to supplement the limited 3rd rail supply. This would enable higher acceleration rates.

It would also add more weight, and albeit change some designs of trains as you'd have to reshuffle somethings to fit them. Plus those batteries would have to be a hefty Voltage.

 

[reddragon]

It would also add more weight, and albeit change some designs of trains as you'd have to reshuffle somethings to fit them. Plus those batteries would have to be a hefty Voltage.

Voltage wise there are already battery powered HGVs, buses, ships & trains, so not an issue.

Weight to power will always be an issue and a battery would be sized for rapid acceleration during the short power peaks so has no need to be large.

 

[yorksrob]

Yes, third rail is terrible at acceleration - because it's fixed to the ground.

B-boom tish.

(Sorry - couldn't help myself).

 

[paul1609]

The Class 465s were (and I believe still are) the fastest accelerating juice rail units in the country. A 12-car Electrostar set, on the other hand, is one of the slowest acelerating trains! The main issue with faster acceleration is power supply, which the juice rail just can't deliver.* AC units can accelerate much faster due to the higher power supply compared to the ground-mounted third rail.

*having said that, the Helsinki Metro uses bottom-contact third rail and our CAF units do very much push you back in your seat/through you down the train, despite only having 75% axles motored and still having their acceleration limited.

It very much depends on where the units are. The performance of a 12 car 375 on the Southeastern Mainline where the power supply was enhanced for the Eurostar service will comfortably see off any of the comparable units on the Brighton Mainline or any of the comparable Siemens units on the Bournemouth Line.

 

[reddragon]

Yes, third rail is terrible at acceleration - because it's fixed to the ground.

B-boom tish.

(Sorry - couldn't help myself).

About a third of the return current on 3rd rail leaks away to buried assets, ground or anything metallic.

It has fried metal fixing in tunnels, Sevenoaks was the worst I know even melting the running rails. It dissolves OLE bases, the NLL was a pain. It also turns water mains into sieves, leaking & accelerating the cycle.

To resolve this LUL uses 4 rail & split voltages, the ELL has copper mats to capture losses & return them to the sub station.

Higher voltages arc, higher currents leak. Only OLE reduces this sufficiently but even this can make over bridge live or induce currents in parallel assets.

 

[paul1609]

A simple solution available today is to install batteries to supplement the limited 3rd rail supply. This would enable higher acceleration rates.

Its not really a solution because power used to charge the batteries isnt available to accelerate the train. All the modern dc trains have much more theoretical power available but are limited by the demands on the power system. Yes you can charge batteries in a hybrid solution at the expense of regeneration to the system but the extra weight of the batteries and complexity of the system mean that nearly all the theoretical benefits are lost. See Chilterns abandonment of their hybrid trains.

 

[stuu]

777s and lu stock are considered light rail however?

By who? Of course they aren't

 

[reddragon]

Its not really a solution because power used to charge the batteries isnt available to accelerate the train. All the modern dc trains have much more theoretical power available but are limited by the demands on the power system. Yes you can charge batteries in a hybrid solution at the expense of regeneration to the system but the extra weight of the batteries and complexity of the system mean that nearly all the theoretical benefits are lost. See Chilterns abandonment of their hybrid trains.

You charge the batteries when no power is drawn or from regen, you accelerate the train with the 3rd rail plus battery power. Simple.

Chiltern abandoned it project on cost, not practicality or viability. The UK still provides substantial subsidies to fossil fuels resulting in us having amongst the lowest oil & gas prices in Europe. On the other hand, it ties electric prices to gas prices & adds other taxes resulting in us having amongst the highest electric prices in Europe.

This is about our countries taxation policies, not the viability of the solution

 

[yorksrob]

About a third of the return current on 3rd rail leaks away to buried assets, ground or anything metallic.

It has fried metal fixing in tunnels, Sevenoaks was the worst I know even melting the running rails. It dissolves OLE bases, the NLL was a pain. It also turns water mains into sieves, leaking & accelerating the cycle.

To resolve this LUL uses 4 rail & split voltages, the ELL has copper mats to capture losses & return them to the sub station.

Higher voltages arc, higher currents leak. Only OLE reduces this sufficiently but even this can make over bridge live or induce currents in parallel assets.

From living in Kent for many years, I remember that Sevenoaks tunnel often needed works on it !

 

[Dunfanaghy Rd]

The first time I rode on a 350 I couldn't believe how it took off from rest. Being used to the 450s I assumed that the difference was down to the relative availability of volts, as they are the same units under the skin.
Pat

 

[paul1609]

You charge the batteries when no power is drawn or from regen, you accelerate the train with the 3rd rail plus battery power. Simple.

Chiltern abandoned it project on cost, not practicality or viability. The UK still provides substantial subsidies to fossil fuels resulting in us having amongst the lowest oil & gas prices in Europe. On the other hand, it ties electric prices to gas prices & adds other taxes resulting in us having amongst the highest electric prices in Europe.

This is about our countries taxation policies, not the viability of the solution

It doesnt work like that because the Southern DC power supply was speccd on the number of trains actually under power at anytime. So if for example you have 5x 12 coach trains at Gatwick Airport drawing power from the supply to charge their batteries you have at peak times to reduce the amount of power that is drawn by other trains on the move in the same section. So they have to accelerate slower.
The East Grinstead Line is a classic example the electrification was specd on the the basis when the Electrostars were introduced that the Uckfield Line would always be diesel trains so there is actually no power available for the Uckfield trains to run on electric between South Croydon and Hurst Green let alone charge batteries. The effect is that Battery Uckfield trains would have to run on Battery once they left the Brighton Main Line which puts Uckfield out of range. Its not even a simple case of upgrading the power supplies because the DNOs power distribution systems in Kent and Sussex are pretty much maxed out.

 

[aleggatta]

I mean, batteries to supplement 3rd rail sounds like a good solution to me, but I would have trackside batteries that could trickle charge off peak and discharge in the peaks, providing extra power straight to the 3rd rail, removing any modifications to trains?

Thinking about it, add regen braking into the mix and you could create a much more efficient 3rd rail system with multiple smaller batteries tied to each third rail isolation area.

 

[paul1609]

I mean, batteries to supplement 3rd rail sounds like a good solution to me, but I would have trackside batteries that could trickle charge off peak and discharge in the peaks, providing extra power straight to the 3rd rail, removing any modifications to trains?

Thinking about it, add regen braking into the mix and you could create a much more efficient 3rd rail system with multiple smaller batteries tied to each third rail isolation area.

I think the problem is that the available power has to be shared by all the trains on the single power supply. this is currently achieved by software in the traction packages which limit the train to its share of the power in the worst possible scenario. Im sure you could come up with a solution where the lineside batteries communicated their state to each train in its section but it would be incredibly complicated.

 

[Samzino]

I don't think there is a battery that could handle such stresses on the market atm. It would be discharging and recharging at a nuts rate especially with 10car and 12 cars.

The first time I rode on a 350 I couldn't believe how it took off from rest. Being used to the 450s I assumed that the difference was down to the relative availability of volts, as they are the same units under the skin.
Pat

Indeed another example was how rapid the 365s under the wire were compared to the 465s on the 3rd rail. 377/7s also on the lightning rod are noticeably slower than under the wire.

 

[CarrotPie]

It very much depends on where the units are. The performance of a 12 car 375 on the Southeastern Mainline, where the power supply was enhanced for the Eurostar service will comfortably see off any of the comparable units on the Brighton Mainline or any of the comparable Siemens units on the Bournemouth Line.

This illustrates another point about power supply: a 12-car 375 set on the Chatham Main Line accelerates at snail's pace, but less so on the SEML.

 

[Irascible]

Its not really a solution because power used to charge the batteries isnt available to accelerate the train. All the modern dc trains have much more theoretical power available but are limited by the demands on the power system. Yes you can charge batteries in a hybrid solution at the expense of regeneration to the system but the extra weight of the batteries and complexity of the system mean that nearly all the theoretical benefits are lost. See Chilterns abandonment of their hybrid trains.

Power supply is specced for peak power draw - which would be a bunch of trains all accelerating at once. If they don't draw more current accelerating than just cruising because the peak power draw is coming out of the battery, you can allow more trains on the same section and your power draw is going to be fairly constant - and/or the train can draw more power than the external supply can deliver.

I mean, batteries to supplement 3rd rail sounds like a good solution to me, but I would have trackside batteries that could trickle charge off peak and discharge in the peaks, providing extra power straight to the 3rd rail, removing any modifications to trains?

Thinking about it, add regen braking into the mix and you could create a much more efficient 3rd rail system with multiple smaller batteries tied to each third rail isolation area.

You'd lose a lot regenning into trackside batteries, you're going both ways through the not very efficient 3rd rail distribution system. Would be better for HV overhead where transmission losses are lower. You could just store & pull power directly from other trains though, that's only one transmission loss.