Networker Braking

[TheJRB]

I was at Rochester on Saturday and noticed that 466006 appears (although I only heard it briefly, so I may be wrong) to have regenerative (that's the right term for when it makes the accelerating sound in reverse while braking isn't it, or is it rheostatic?) braking enabled. I've seen this talked about and from what I've read it seems that this was due to happen to all 465/9s and 466s but I haven't seen any before with this enabled. Can anybody provide any further details as to whether this is happening throughout the fleet, if that's just a one off, or if I'm totally wrong?

 

[Nym]

When it makes 'motoring' sounds when braking it could be any number of things...

Regenerative and Rheostatic braking both do exactly the same thing through the motor, but regenerative is then fed using power electronics back into the grid, where as rheostatic is sent to a resistor bank or heaters to disperse energy.

The same sound is also made on 323 units during negative accelaration, because thats what them units are doing, accelarating backwards.

(In effect, shoving it into reverse and riding out the clutch while braking)

Anyway, just done a small amount of reading, when it whines down 'the other way' on 323s it is different to networkers, using a 3phase motor (although knowing what kind would mean that I can provide a full explanation) through solid state convertors means it will more than likely be regenerative braking at the top end of the braking scale and rheostatic at the bottom end, as higher frequencies are easyer to rectify with solid state devices to feed back into the DC Grid.

Of course, if regenerative braking is to be disabled for any reason, they could possible revert back to reverse motoring, but without knowing the spesifics of the traction systems and refering back to some of my older books I can't give you an in depth technical awnser.

To summerise there are three kinds of braking available with this type of traction system

(Solid State 3 Phase controlled AC Inversion)

Reverse Motoring (Slam it into reverse)
Regenerative (Motor becomes a generator and sends energy, via rectifiers, proberbly thyistor based, back to the grid)
Rehostatic (Feeds to resistors and dicipates the energy as heat)

 

[466.networkers]

I think 466006 having it's regenerative braking reenabled is a one off, having only been on it and 466022 after their relivery I don't know if it is a one off trial or if it will be rolled out across the rest of the fleet.

It does sound pretty awesome though! :P

Thanks
Ryan

 

[TheJRB]

Thank you Nym for the explanation, that helps a lot. The exact three phase motor is, according to Platform 5's EMUs and Light Railway pocket book, a GEC-Alsthom G352BY on the 465/2 and 465/9s with GEC-Alsthom G352AY on the 466s, if that helps.
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I think 466006 having it's regenerative braking reenabled is a one off, having only been on it and 466022 after their relivery I don't know if it is a one off trial or if it will be rolled out across the rest of the fleet.

It does sound pretty awesome though! :P

Thanks
Ryan

I certainly agree; it sounds great and better than the normal quiet arrival from the /9s, /2s and 466s. It will be interesting to see if this happens to the rest of the class.

 

[Nym]

Thank you Nym for the explanation, that helps a lot. The exact three phase motor is, according to Platform 5's EMUs and Light Railway pocket book, a GEC-Alsthom G352BY on the 465/2 and 465/9s with GEC-Alsthom G352AY on the 466s, if that helps.
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I certainly agree; it sounds great and better than the normal quiet arrival from the /9s, /2s and 466s. It will be interesting to see if this happens to the rest of the class.

Well, more need to know if the're Syncronous Machines or Induction Machines... I'll look into it tomorow evening if you'd like a full explanation...

 

[TheJRB]

Well, more need to know if the're Syncronous Machines or Induction Machines... I'll look into it tomorow evening if you'd like a full explanation...

According to Wikipedia, they are induction motors. I admit I've never really thought about the details of train brakes, but this is interesting. I appreciate your explanation, but please don't spend too much time on this for me! I doubt I have the technical expertise to truly grasp the topic at hand.

 

[Nym]

It's to do with magnets pulling at different angles that are changed by the power electronics, by the stator or rotor, with a changing magnetic field in the gap. If you'd like to know more than that, lemme know...

 

[SprinterMan]

When it makes 'motoring' sounds when braking it could be any number of things...

Regenerative and Rheostatic braking both do exactly the same thing through the motor, but regenerative is then fed using power electronics back into the grid, where as rheostatic is sent to a resistor bank or heaters to disperse energy.

The same sound is also made on 323 units during negative accelaration, because thats what them units are doing, accelarating backwards.

(In effect, shoving it into reverse and riding out the clutch while braking)

Anyway, just done a small amount of reading, when it whines down 'the other way' on 323s it is different to networkers, using a 3phase motor (although knowing what kind would mean that I can provide a full explanation) through solid state convertors means it will more than likely be regenerative braking at the top end of the braking scale and rheostatic at the bottom end, as higher frequencies are easyer to rectify with solid state devices to feed back into the DC Grid.

Of course, if regenerative braking is to be disabled for any reason, they could possible revert back to reverse motoring, but without knowing the spesifics of the traction systems and refering back to some of my older books I can't give you an in depth technical awnser.

To summerise there are three kinds of braking available with this type of traction system

(Solid State 3 Phase controlled AC Inversion)

Reverse Motoring (Slam it into reverse)
Regenerative (Motor becomes a generator and sends energy, via rectifiers, proberbly thyistor based, back to the grid)
Rehostatic (Feeds to resistors and dicipates the energy as heat)

Sorry if this is a stupid question, but doesn't this damage/overheat the motors?

 

[es373]

It's to do with magnets pulling at different angles that are changed by the power electronics, by the stator or rotor, with a changing magnetic field in the gap. If you'd like to know more than that, lemme know...

Sounds like Electro Motive Force?
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Sorry if this is a stupid question, but doesn't this damage/overheat the motors?

Overheat? Shouldn't do, that's why we have traction motor blowers.
I don't think the motors do turn backwards. Well, my DC ones don't anyway.
I always thought regen worked on the basis that electrical flow is changed and put back into the grid via booster transformers and return circuits or stored in a bank of capacitors/batteries for auxiliary use?
Maybe I'm wrong.

 

[millemille]

Right, let's clear up some myths here....

All classes of DC Notworkers have been capable of rheostatic and regenerative braking since they were delivered in the early 1990's. Rheo has been is use all of the time (although in the past at nay one time a large percentage of the fleet have not had it working for a variety of technical and maintenance reasons and understand that rheo, even working fully won't operate consistently at each and every brake application as the grids heat up and the rheo cuts out to prevent searingly hot air being blown out from the underside of the train and starting fires - as happened when the Electrostars were first introduced on the SE network). Regen was not in use until the last couple of years as the infrastructure wasn't capable of receiving the generated power. SE pushed to get all classes of train they operated actually capable of regen'ing - hence the increase in the number of units where the rheo was working, because you can't regen if rheo isn't working - in order to get a discount of the EC4T component of their track access charge.

You can't hear any difference between rheo and regen, other than on regen the blower motor won't run as the resistors grids don't heat up, as the traction equipment is doing exactly the same job, it's just what happens to the generated power that is different.

You can't put an Networker into reverse whilst it's moving forward.

 

[Galvanize]

I rode 466006 on my way into work a couple of weeks back. It was pulling into Lewisham, and I could hear the motors winding down...thought "Right, I wanna sit in the motor car to relive those memories!"

It was using Rheostatic, as I could hear the fans whirring away while the train was stationary, obviously as MilleMille posted, to cool the motors down!

Dunno if this was true or not, but people used to say the small white light, visible in the windscreen on 465s/466s were there to show whether Rheo/Regen was enabled or disabled!

 

[es373]

I rode 466006 on my way into work a couple of weeks back. It was pulling into Lewisham, and I could hear the motors winding down...thought "Right, I wanna sit in the motor car to relive those memories!"

It was using Rheostatic, as I could hear the fans whirring away while the train was stationary, obviously as MilleMille posted, to cool the motors down!

Dunno if this was true or not, but people used to say the small white light, visible in the windscreen on 465s/466s were there to show whether Rheo/Regen was enabled or disabled!

Don't motor blowers only wind up when driver takes power? I think you're referring to the resistor cooling fans? I'm not very familiar with Networkers

 

[millemille]

I rode 466006 on my way into work a couple of weeks back. It was pulling into Lewisham, and I could hear the motors winding down...thought "Right, I wanna sit in the motor car to relive those memories!"

It was using Rheostatic, as I could hear the fans whirring away while the train was stationary, obviously as MilleMille posted, to cool the motors down!

Dunno if this was true or not, but people used to say the small white light, visible in the windscreen on 465s/466s were there to show whether Rheo/Regen was enabled or disabled!

The fan motors cool the rheo grids.

Yes, under the PIS on the 2nd mans side of the Notworkers are 2 lights, one for safety systems isolated and the other for Regen isolated.

 

[Nym]

Sorry if this is a stupid question, but doesn't this damage/overheat the motors?

OK that was an over simplification...

Hence why I said it's like reversing and riding the clutch (I don't know if anyone has ever had to do that with shattered brakes, it's scary...)

Motors, especially induction machines (mainly whats used on trains), can have both a positive and negative rate of angular acceleration, denoted by the 'slip' of the machine, the magnetic Field between the rotor and the stator, what I'm referring to as reverse motoring isn't actually reversing the motor, it's slowing the stator field to push the system into negative slip, so the magnetic force in the air gap is working to slow down the speed of rotation of the machine, rather than increase it, all of this is controlled by the three phase inverter power electronics in software / complex hardware.

If that's too complicated to understand get back to me and I'll try and find a middle ground.

Over Simplification of slip = The force between the rotor and stator with respect to the angle.

So no, it won't damage the machine more so than using it in the other direction. It would however warm up more.

EDIT: I've not touched induction machines for a couple of years so I'd need to dig out some of me old notes and can get some numbers about how it would heat up if you like, theres also the stator current to think about, as dependant on whats happening with the rotor current and how the braking is being regenerative, when it is using the motors to brake, it could in effect generate a DC Current across the Rotor.

 

[es373]

OK that was an over simplification...

Hence why I said it's like reversing and riding the clutch (I don't know if anyone has ever had to do that with shattered brakes, it's scary...)

Motors, especially induction machines (mainly whats used on trains), can have both a positive and negative rate of angular acceleration, denoted by the 'slip' of the machine, the magnetic Field between the rotor and the stator, what I'm referring to as reverse motoring isn't actually reversing the motor, it's slowing the stator field to push the system into negative slip, so the magnetic force in the air gap is working to slow down the speed of rotation of the machine, rather than increase it, all of this is controlled by the three phase inverter power electronics in software / complex hardware.

If that's too complicated to understand get back to me and I'll try and find a middle ground.

Over Simplification of slip = The force between the rotor and stator with respect to the angle.

So no, it won't damage the machine more so than using it in the other direction. It would however warm up more.

EDIT: I've not touched induction machines for a couple of years so I'd need to dig out some of me old notes and can get some numbers about how it would heat up if you like, theres also the stator current to think about, as dependant on whats happening with the rotor current and how the braking is being regenerative, when it is using the motors to brake, it could in effect generate a DC Current across the Rotor.

Weak fielding?

 

[Class 466]

466042 has also had Rheostatic Braking Enabled

 

[466.networkers]

466042 has also had Rheostatic Braking Enabled

It's REGENERATIVE, not rheostatic!

 

[Class 466]

No, it's rheostatic because when the train stops the fans start which cools down the rheostatic system 465/466s haven't been cleared to use regen braking I asked the driver :P
http://en.m.wikipedia.org/wiki/Dynamic_braking

 

[apk55]

Having done some work in the past on electronic motor control systems my impression is that most trains are designed to be permanently regenerative but with the addition of an electronically controlled dump resistor across the line that can be switched on if the line voltage exceeds a particular value (probably around 850V on UK third rail systems) so converting the unit to rheostatic braking. Definitely with a typical DC to three phase converter to motor, the system is inherently regenerative it is just a matter of timing control for the power switching devices.

Dynamic braking increases the motor and associated control electronics losses as it has to work during braking, therefore better cooling is required so they may have to be force cooled by a fan.

On some systems the dump resistor may short time rated so that if there are no other trains drawing power on the section the unit may revert to friction braking. Otherwise they may be force cooled with a fan.

 

[HSTEd]

Weak fielding?

The field current stays the same as it would normally, but by messing around with the drive current frequency using the traction electronics you can make the motor spin more rapidly than its equilibrium velocity so it will then attempt to "spin down" to equilibrium by generating energy which you can then disperse however you like.

You have to remember that induction motors have an equilibrium rev count where they will generate no torque and that normally they are rotating slower than there equilibrium speed and consuming energy in an attempt to increase speed to reach it.

A similar principle is used to generate electricity from a variable speed drive on a wind turbine.

EDIT: Don't modern regen-equipped substations allow traction power to be returned to the AC power grid?

 

[es373]

Yeah I know what Weak Fielding is mate... was getting a bit confused with what he was trying to explain.
Sorry!

 

[Class 466]

Turns out its Dynamic Blended Braking as once the train reduces to below 5 mph the normal disc brakes finish the job and bring the train to a halt.

 

[es373]

Brake blending***