Traction Current returned to the electrified rail/Over head lines under braking.

[musicking1306]

I have heard in lots of different places about some electrical trains return electricity to the overhead lines/ 3rd rail when Braking/ slowing down. I was wondering if this was just a publicity stunt for train operating companies to make them look more environmental friendly.

I was asking this because my physics A Level textbook takes about trains returning current to the rails/overhead lines and I always thought that it was just the traction motors pushing the other way.

I have heard this thing about returning electricity to the rails/OHL in a number of places such as on London Underground and on Eurostar.

1) Does the trains use traction motors to slow the train (push the other way)if not then what does slow the train (apart from Breaks that cause friction on the wheel)

2) Does this method of slowing the train create electricity and if so is it returned to the 3rd rail or overhead line equipment.

3) Which trains use this technology?

 

[rebmcr]

I have heard in lots of different places about some electrical trains return electricity to the overhead lines/ 3rd rail when Braking/ slowing down. I was wondering if this was just a publicity stunt for train operating companies to make them look more environmental friendly.

I was asking this because my physics A Level textbook takes about trains returning current to the rails/overhead lines and I always thought that it was just the traction motors pushing the other way.

I have heard this thing about returning electricity to the rails/OHL in a number of places such as on London Underground and on Eurostar.

1) Does the trains use traction motors to slow the train (push the other way)if not then what does slow the train (apart from Breaks that cause friction on the wheel)

2) Does this method of slowing the train create electricity and if so is it returned to the 3rd rail or overhead line equipment.

3) Which trains use this technology?

There are four main types of braking a train. Two are mechanical and two are electrical.

The mechanical types either push a brake shoe onto the running wheel itself (this has a nice side effect of scrubbing crushed leaves off them), or use a traditional brake drum/disc (which caused problems with dirty wheels not operating signalling when first introduced).

The electrical types do indeed use the traction motor to 'push the other way'. Now the energy has to go somewhere due to the laws of physics, so the older method, Rheostatic, uses a roof-mounted array of resistors to turn the electricity coming out of the motors (temporarily functioning as generators) into heat, and dump the energy into the passing air. Those are what short-circuited on the Eurostar when the show melted.

With advances in traction motors, and in the electrical supply, it is now possible to return this 'free' electricity to the wire or the third rail. This is called Regenerative. I believe it's planned on the tube's Victoria Line pending supply upgrades, and is enabled on new sub-surface stock on the Metropolitan line, but is sharing track with older carriages that can't take it yet.

Additionally, trams usually have an emergency brake that consists of a great big magnet that energises and clamps directly onto the track (usually damaging it) when used.

 

[jopsuk]

I know South West Trains use it on their Desiros. Pretty sure SET Networkers do it as well. Not sure about electrostars.

There's even diesels have a version of it- the Voyagers, Super Voyagers and Meridians can use their electric traction motors to produce electricity. This electricity is then passed through large resistors on the roof which produce heat. This might seem wasteful, but both this and full regenerative braking is better for the wheels- at higher speeds its an effective form of anti-lock braking. It reduces wear on disc brakes/on the wheel tread if tread brakes are used

 

[musicking1306]

There are four main types of braking a train. Two are mechanical and two are electrical.

The electrical types do indeed use the traction motor to 'push the other way'. Now the energy has to go somewhere due to the laws of physics, so the older method, Rheostatic, uses a roof-mounted array of resistors to turn the electricity coming out of the motors (temporarily functioning as generators) into heat, and dump the energy into the passing air. Those are what short-circuited on the Eurostar when the show melted.

I would have thought that the action of the traction motors pushing the other way world withdraw traction current just as if you stick a car in reverse then it still uses fuel to slow the car down.

 

[PaxVobiscum]

I know South West Trains use it on their Desiros. Pretty sure SET Networkers do it as well.

Here's an article for starters:
http://www.southwesttrains.co.uk/Launch-of-regenerative-braking.aspx

The whole fleet of 30 Class 458 trains is expected to be fitted with the new regenerative braking software by the summer 2011. The system will then be rolled out to South West Trains’ fleet of 172 state-of-the-art Desiro trains.

 

[rebmcr]

I would have thought that the action of the traction motors pushing the other way world withdraw traction current just as if you stick a car in reverse then it still uses fuel to slow the car down.

If you manage to stick a car in reverse at speed, your gearbox is likely to be left on the road. Internal combustion engines only go one way and there's too much energy in a moving car for a reverse gear cog to cope with.
It is possible to slow a car down with the engine, by shifting down and letting the increased relative air pressure in the piston cylinders push against the gear cog (and by extension the wheels) enough to slow down but not enough to bust anything or stall the engine.
Also an internal combustion engine will always use fuel, even when idling. It's basically a chain reaction of explosions, and the chain has to keep going (that's why it's one way only).

Electric motors are completely different and it really is as simple as it sounds for pushing one way or another way, putting energy into the system or producing energy from it.

 

[466.networkers]

I know South West Trains use it on their Desiros. Pretty sure SET Networkers do it as well. Not sure about electrostars.

Other way round. All SE 375 and 376 Electrostars are rheostatic enabled. Some of the Hitachi 465/0 and /1 have had their rheostatic braking enabled for the leaf fall (may be permanent, not sure yet) and of course the Hitachi Class 395s has rheostatic braking when on AC and DC.

 

[Nym]

It's not as simple as people make out to be honest, it's not just a case of reversing the motors, all that would do is warm them up a lot. To have a cat in heck's chance of knowing what happens you'd need to know how AC synchronous motors work, and I'm guessing this is in the Salters Horners Physics A Level text book, and if so, you won't know this yet.

PM or poke me for more info.

 

[millemille]

Other way round. All SE 375 and 376 Electrostars are rheostatic enabled. Some of the Hitachi 465/0 and /1 have had their rheostatic braking enabled for the leaf fall (may be permanent, not sure yet) and of course the Hitachi Class 395s has rheostatic braking when on AC and DC.

All Southeastern operated stock have their dynamic braking enabled and are capable of rheo and regen braking.

The recent enablement of the BREL built 465's dynamic braking had nothing to with the leaf fall season and what makes you not sure it's permanent?

 

[Bushy]

Other way round. All SE 375 and 376 Electrostars are rheostatic enabled. Some of the Hitachi 465/0 and /1 have had their rheostatic braking enabled for the leaf fall (may be permanent, not sure yet) and of course the Hitachi Class 395s has rheostatic braking when on AC and DC.

Many sources indicate that 465s are equipped for regen braking but were fitted with with resistor grids for areas where the infrastructure could not accommodate it. Although it is now a long time ago, I seem to remember that NSE pushed regen braking as one of the benefits of Networkers.

For LU one of the advantages of regen braking is the reduction of the heat that is dissipated into the tunnels by mechanical braking.

Regards

Bushy

 

[Nym]

Many sources indicate that 465s are equipped for regen braking but were fitted with with resistor grids for areas where the infrastructure could not accommodate it. Although it is now a long time ago, I seem to remember that NSE pushed regen braking as one of the benefits of Networkers.

For LU one of the advantages of regen braking is the reduction of the heat that is dissipated into the tunnels by mechanical braking.

Regards

Bushy

The thing with LU using regenerative braking is that it requires a major upgrade of each rectifier set on the line for it to be able to be used.

 

[Ediswan]

At the most basic level, you are using the motor as a generator. If you can find a bicyle with a dynamo, you will be able to feel the dynamo acting as a brake when the lights are on.

I do agree that making this work with the motors in question, then getting the power back to the track, is not so simple.

 

[455driver]

It's not as simple as people make out to be honest,

Motor used as a generator to produce elecktrickery, this elecktrickery is then either sent through the resistor banks (rheostats) and dissipated as heat or returned to the OHL or CRE.

Seems simple enough to me!

As you like to complicate matters can you explain to me how the 76s were fitted with regenerative braking back in the 1950s? Dont think they had asynchronous motors?

I aint poking anyone till we have been on a few dates!

 

[jopsuk]

It's not as simple as people make out to be honest, it's not just a case of reversing the motors, all that would do is warm them up a lot. To have a cat in heck's chance of knowing what happens you'd need to know how AC synchronous motors work, and I'm guessing this is in the Salters Horners Physics A Level text book, and if so, you won't know this yet.

PM or poke me for more info.

The useful "lie to children" though that helps people without knowledge of how the motors work in detail though is that "running the motor in reverse produces power that can be put back into the 3rd rail or OHL".

For most people, that's enough of an explanation.

 

[swt_passenger]

I think an odd thing about this subject is that the terminology used is confusing for some historic reason. Rheostatic braking seems to me to be a variant of regenerative braking, but the the way things have developed over the years the term 'regenerative' is normally used only when describing the type of 're-gen' where the energy is passed back into the supply side, or 'out of' the train.

I'd also just add for the original poster's benefit that in AC electrification areas the recovered energy can be passed back through transformers into the distribution system, (aka 'the grid') but in the DC third rail supply area, (and presumably on LU as well), the rectifiers in the supply system are generally not reversible, (not inverters) so any recovered energy from braking has to be utilised by other trains in the area. One of the issues they were worried about in the outer reaches of the DC network was that regenerative braking would not be practical if there were few trains about to receive the power. So the trains have to continually monitor the supply side voltage, and if it increases too much they automatically revert to rheostatic braking.

 

[455driver]

Adding to Jopsuks post,

Take a 12V motor and connect it to a 12V bulb, spin the shaft of the motor fast enough and the bulb will light, that is effectively what a traction motor does.

 

[O L Leigh]

Motor used as a generator to produce elecktrickery, this elecktrickery is then either sent through the resistor banks (rheostats) and dissipated as heat or returned to the OHL or CRE.

Seems simple enough to me!

As you like to complicate matters can you explain to me how the 76s were fitted with regenerative braking back in the 1950s? Dont think they had asynchronous motors?

I aint poking anyone till we have been on a few dates!

Nope, but the Cl76s ran on 1500V DC which is an easier type of electrickery to deal with. Using AC or AC motors and their associated wizardry is much more difficult.

But without complicating matters unnecessarily, there is no difference between motors and generators. If you take the dynamo off your bicycle and pass electricity through the terminals it will turn like a motor. At their most basic level, they are effectively the same piece of equipment.

O L Leigh

 

[Nym]

Motor used as a generator to produce elecktrickery, this elecktrickery is then either sent through the resistor banks (rheostats) and dissipated as heat or returned to the OHL or CRE.

Seems simple enough to me!

As you like to complicate matters can you explain to me how the 76s were fitted with regenerative braking back in the 1950s? Dont think they had asynchronous motors?

I aint poking anyone till we have been on a few dates!

That would be because doing this in a PM/EM Stator Field DC system is about four million times less complicated than doing it in a synchronous AC system...

One of the issues they were worried about in the outer reaches of the DC network was that regenerative braking would not be practical if there were few trains about to receive the power. So the trains have to continually monitor the supply side voltage, and if it increases too much they automatically revert to rheostatic braking.

Or where you have DC escalators and a train regenerated on the way into the station, the escalators speed up as the voltage spiked
--- old post above --- --- new post below ---

Nope, but the Cl76s ran on 1500V DC which is an easier type of electrickery to deal with. Using AC or AC motors and their associated wizardry is much more difficult.

But without complicating matters unnecessarily, there is no difference between motors and generators. If you take the dynamo off your bicycle and pass electricity through the terminals it will turn like a motor. At their most basic level, they are effectively the same piece of equipment.

O L Leigh

Yes, for rotor/stator motors

Try it with a BLDC or Stepper...

Should I post the long explanation for everyone to pick to peices that I sent via PM???

 

[O L Leigh]

I don't think the OP needs that level of detail. Yes regenerative braking is not only possible but in everyday use across the network. The componentry and associated mind-f***ing is not necessary to understand unless you really HAVE to understand it.

O L Leigh

 

[swt_passenger]

We should by now have (re)generated just enough info for musicking1306 to become the class know-all, anyway...

 

[Nym]

We should by now have (re)generated just enough info for musicking1306 to become the class know-all, anyway...

You should see the PM he got...

Went through some of the basic aspects of synchrnous motors in a chapter long enough to accomadate the average bowel movment...

 

[O L Leigh]

1) Does the trains use traction motors to slow the train (push the other way)if not then what does slow the train (apart from Breaks that cause friction on the wheel)

Effectively, that is exactly what happens.

2) Does this method of slowing the train create electricity and if so is it returned to the 3rd rail or overhead line equipment.

Yes it does. Some older trains have a rheostatic brake (sometimes called dynamic brake) which waste the electrical energy generated by this braking system as heat using banks of resistors, but more modern trains return the power to the traction supply system.

3) Which trains use this technology?

Most electric units from the mid-1990s onwards use a regenerative brake. Networkers, Desiros, Electrostars and Cl323s have regenerative brake.

Is there any more required...?

O L Leigh

 

[Ediswan]

Somewhat off-topic, but DC to AC inverters have got a lot cheaper. Thats is how all those electrovoltaic panels on domestic roofs can feed the grid. They do come in larger sizes.

 

[musicking1306]

You should see the PM he got...

Went through some of the basic aspects of synchrnous motors in a chapter long enough to accomadate the average bowel movment...

Yes thank you to all of you as I have learn a lot more than most people do between 20:00 and 21:30 on a normal week night. I really wasn't aware of the simplicity of the technology that is involved and that trains are far more intelligent than I thought, to notice if they are effecting the electrical supply current from 3rd rails. Thanks Nym for the explanation of the motors and the magnetic fields associated with the regeneration of electricity through braking.

Tom

 

[Nym]

Somewhat off-topic, but DC to AC inverters have got a lot cheaper. Thats is how all those electrovoltaic panels on domestic roofs can feed the grid. They do come in larger sizes.

They have, but to get one that meets the standards required regarding harmonics for generation they're still not cheap, as you need to put in (most of the time unless you go to very expensive multi level multi pulse AC waveform generators) system side filters, and then you're actually filtering the grid, not just your side of the meter / CT chamber, but everyone else's flat screen tele and dyson hover in the area, pretty much all the way back to the nearest 11kV sub. Hence, grid connectable stuff is still not that cheap...

 

[TGV]

Eurostars don't have regen capability. Rheostatic only. 3 phase AC asynchronous motors (big ones) and a few large fans and resistor banks to chew on the end of them when they're excited into rheo.

You can really clearly hear them if you walk into either the first or last carriage after the train passes through Stratford on the way into London and slows to St P. Bloody loud. Way louder than the motor blowers, transformer fans or compressors.

 

[millemille]

Many sources indicate that 465s are equipped for regen braking but were fitted with with resistor grids for areas where the infrastructure could not accommodate it. Although it is now a long time ago, I seem to remember that NSE pushed regen braking as one of the benefits of Networkers.



Regards

Bushy

All 465/466's have been capable of rheo and regen braking from day 1.

You can't have regen without functioning rheo brake, if the network becomes unreceptive and the train has to drop out of regen braking it reverts to rheo not friction braking.

There have been, and still are, reliability issues with the dynamic braking equipment ,and also with drive train components subject to additional load when dynamic braking is enabled, which have prompted various periods of dynamic brake isolation in the past 20 years.

Right now all Networkers have dynamic brake enabled and are capable of regen braking - one sub fleet has issues with component reliability which means that some units have dynamic brake isolated due to defects but this will be addressed at the next level 5 overhaul.

 

[captainbigun]

Eurostars don't have regen capability. Rheostatic only. 3 phase AC asynchronous motors (big ones) and a few large fans and resistor banks to chew on the end of them when they're excited into rheo.

You can really clearly hear them if you walk into either the first or last carriage after the train passes through Stratford on the way into London and slows to St P. Bloody loud. Way louder than the motor blowers, transformer fans or compressors.

Rectifier front end on a Eurostar is the issue there I believe. 92s the same.

 

[O L Leigh]

You can't have regen without functioning rheo brake, if the network becomes unreceptive and the train has to drop out of regen braking it reverts to rheo not friction braking.

Are you just talking about Networkers?

If Cl379s lose regen they go straight to friction. I expect other classes do too.

O L Leigh

 

[millemille]

Are you just talking about Networkers?

If Cl379s lose regen they go straight to friction. I expect other classes do too.

O L Leigh

Networker and E* DC units revert to rheo from regen and if rheo isn't working they don't regen in the first place.

AC units might well be different because of the 4Q converter and phase alignment meaning they can't revert to rheo from regen - haven't dealt with AC units for a good few years now.