British Diesel-Electric Traction Motor Control - methods?

[ZiderHead]

Ive been trying to find out about traction motor control in british diesels and am really struggling to find anything. I assume something like a CL60 is pretty sophisticated with plenty of ECUs and something similar to modern car traction control, but applied to 6 axles instead of one or two. Something like a EE Type 3 certainly would not, how did they control the traction motors, and how did they deal with wheel slip?

 

Any pointers gratefully received

 

 

Thanks, ZiderHead

[Baby Deltic]

It depends on the age of the locomotive. The early locomotives such as the class 37's had DC generators and DC traction motors with brushes, armatures etc. The general method employed was the use of resistances to control the voltage across the armatures and field windings to control the torque and speed of the motors. They could also be set in parallel, series or shunt to gain the best performance characteristics for a given speed or load. With the advent of solid state control systems, generators could be replaced by alternators and the current rectified before being fed to the traction control equipment. The advantage of this is that alternators don't have brushes unlike generators. With the advancement in electronics and devices such as SCR's the old method of using resistances and switchgear became obsolete. More advances in the field of solid state electronics allowed AC traction motors to be used. These are controlled by voltage and frequency rather than just voltage and current, so the control is more sophisticated, but the advantage of having no brushes, etc is a big one.

[Edwin_m]

Useful info on Wikipedia. 

 

http://en.wikipedia.org/wiki/Traction_motor

[Baby Deltic]

Just to add to my previous post, now that I'm on a proper keyboard instead of a poxy ipod, back in the 1960's Brush traction began to experiment with AC control systems using solid state devices. They bought 10800 off of BR, fitted a Maybach MD 655 and named the locomotive 'Hawk'. The locomotive was used to test the solid state control equipment, but it proved to be very costly because these devices were hellishly expensive to manufacture at the time, and they blew up fairly often, and the project was soon abandoned. It did however pave the way for HS4000 'Kestrel'. EE were also looking in this direction, when the class 50 design was being developed, they fitted their electronic control equipment to the locomotives. It was to prove very troublesome and BR ripped out a lot of kit when they refurbished the loco's. In the 1980's the BR Railway Technical Centre at Derby started to take a serious look at the problems encountered with adhesion and wheelslip. Four class 46's were transferred to the RTC once they were taken out of traffic (46009/023/035/045) for use by the RTC. These became 97401/2/3/4, although only 46035 and 46045 were actually numbered as class 97's. 97403 was used as a test bed for adhesion experiments. The loco was named 'Ixion' after the character who was chained to a revolving flaming wheel for eternity in the Greek myths. One of the axles on 97403 had its traction motor isolated and connected to control equipment in the test vehicles which formed the adhesion test train. I believe a control desk was also removed from one end of the class 46 and placed in the laboratry vehicle from where the tests were carried out. The axle under control was fitted with an encoder to measure axle speed precisely and compare it to train speed, thereby getting the percentage by which the axle speed was greater than train speed when adhesion was at its maximum. The whiole ensemble was hauled by class 24 number 97201 when out on test. The Ixion project provided data that paved the way for SEPEX (SEPerate EXcitation) control which gave locomotives such as the class 60 enormous tractive effort. Of the class 46's at the RTC, 46009 was destroyed in a collision test at Old Dalby in July 1984, 46023 was painted as the standby collision loco should 46009 fail. It was later dumped at Crewe Basford Hall until cut to provide spares for 46035. 46035 was preserved and put back on the main line, and 46045 was preserved.

[Pugsley]

If you want to learn about the first generation of 'modern traction', you can do no better than to get yourself a copy of this:

http://www.ebay.co.uk/itm/BRITISH-RAIL-BRITISH-RAILWAYS-DIESEL-TRACTION-MANUAL-FOR-ENGINEMEN-1962-/140947600808?pt=UK_Collectables_Railwayana_RL&hash=item20d121b5a8#ht_0wt_0

 

It covers pretty much how all of the loco systems work, and also covers hydraulics and DMUs as a bonus! I'm not sure what methods the 60 uses, but it still has DC motors, probably with a lot of electronic controls. AC motors, controlled by inverters, started being used in the US in the early 90's.

[Baby Deltic]

If you want to learn about the first generation of 'modern traction', you can do no better than to get yourself a copy of this:

http://www.ebay.co.uk/itm/BRITISH-RAIL-BRITISH-RAILWAYS-DIESEL-TRACTION-MANUAL-FOR-ENGINEMEN-1962-/140947600808?pt=UK_Collectables_Railwayana_RL&hash=item20d121b5a8#ht_0wt_0

 

It covers pretty much how all of the loco systems work, and also covers hydraulics and DMUs as a bonus! I'm not sure what methods the 60 uses, but it still has DC motors, probably with a lot of electronic controls. AC motors, controlled by inverters, started being used in the US in the early 90's.

 

 That is a very good book. I like the bit on the DMU transmissions.

[ZiderHead]

that book looks rather interesting, will have to pick up a copy. I found some more info at http://www.railway-technical.com/tract-01.shtml too.

 

Thanks for the help gents

[Gary H]

AC traction motors now used by both EMD and GE in the U.S also have no duty rating like DC motors do, ie, they can be worked at full power at low speed without burning out like a DC traction motor is prone to.

AC traction also developes alot more tractive effort. Thats why its now rare to see DC powered locomotives on an American 15'000 ton coal train as the likelehood of cooking DC traction motors increases on those tonnages.

EMD were also responsible for developing "creep control" whaereas each wheel set is alowed to turn very slightly faster than ground speed. This is a computer controlled system. This has the advantage of developing huge tractive effort, more so than a conventional system where any slip is stopped.

There's a good video of it in action here in India on a WG4 loco but its the same system used on the Class 59 and loco's in the states.

[ZiderHead]

that always seems really counterintuitive - that you get more grip when the wheel is slipping a little. IIRC cars traction control/ABS generally aim for about 5% slip, although I guess the newest systems optimise the amount of slip in realtime depending on the load.

[Gary H]

Here's another good video of a pair of big GE's 'digging in'. This shows the huge advantage of AC traction motors, this would have been game over with DC.

Sorry, i know its not British but its all the same principles!

Those AC4400's are nigh-on 200 tons a piece but they still have the power to slip those wheels.(4400hp).

[ZiderHead]

If you want to learn about the first generation of 'modern traction', you can do no better than to get yourself a copy of this:

http://www.ebay.co.uk/itm/BRITISH-RAIL-BRITISH-RAILWAYS-DIESEL-TRACTION-MANUAL-FOR-ENGINEMEN-1962-/140947600808?pt=UK_Collectables_Railwayana_RL&hash=item20d121b5a8#ht_0wt_0

 

Thanks for the link there Pugsley, that very copy is now heading my way for the princely sum of 99p +P&P

[pheaton]

Traction Motors.....

 

Classic UK diesels employ standard force ventilated DC traction motors connected either all parralell or series parralell accross the main generator (08/09/20/31/UR37/40/44/45/46/47/50/55) or alternator R37 56/ 57/58

 

The traction motor control itself is very simple pictured below is the traction motor arrangement for a class 45

 

 

you can see they connected in parralell across the main generator.

 

When the driver moves the power handle provided the Engine speed valve is powered (this allows the engine to increase in speed) and if the Earth fault relay is not energised, a group of pneumatic contactors will close these physically connectt the motors to the generator in the drawing these are seen as the circles with m1 m2 m3 etc. Then based on the speed of the engine a load regulator will operate changing the excitation level of the main generator which in turn decides how fast the motors turn, based on the drivers power demand.

 

To make the motors go into reverse requires the operation of the locomotives reverser, but lets concentrate on a single motor

 

 

Weve already talked about the general principle in laymans terms on how the motor operates but the reverser as seen in the diagram varies between locomotives on a class 45 its a large rotating drum which physically reverses the connection of the motor accross the generator. Again this pneumatic, as you need an even change accross all of your motors and an electrical fault could cause you to have a motor which hasnt reversed (not good).

 

So what happens if you get a wheel slip.

 

You see above in the main diagram (and again the method varies between locomotive but the principles remain the same) you have 2 wheel slip relays which control 4 of the 6 motors, both relays are wound magenetically opposite and all they do is compare current demand in the 2 groups of two motors, if there is a difference in the current of 130amps in the case of a peak the relay will operate causing power to be cut via the power control relay. When wheel slip occurs the current demands from the slipping motor will drop dramatically compared to the motors that are not slipping.

 

What does the field divert system do.

 

If you take a motor say out of a model train you have an fixed field magnet which means when it gets to 12 volts it will spin at a set speed with a set torque. Fine for a model train but not the real thing, when a real train moves off at slow speed you have a massive current demand (not uncommon to see 7000+ amps on a 47/3) so you are interested in maximum field strength but since if you had a fixed magnet you wouldnt be able to achieve this but the motors of a locomotive do not have fixed magnets, essentially they are electro magents who's behavour can be altered by changing the voltage being passed through the field windings which alter how the motor behaves. A locomotive developes maximum tractive effort (torque) at around 13mph after which the speed increases and the current demand falls.

 

All DC traction motors develop back-EMF which is the motor acting as a generator and countering the power going into it, your current falls to a very low point but your engine may be at full power which means you cant spin the generator any faster for more volts, therefore you must change the way your motors behave and get them to spin faster with the availiable voltage you do this by diverting your field voltage through a set of resistors in a process called field diversion the outcome of this process is in principle the same as changing gear on your car.

What happens if there is a problem.

 

the most common problems is a  traction motor flashover, flashovers can be minor or major, but the outcome is the same a power to earth fault where electricity is able to defeat the insulation of the motor and escape to earth. In the event of a flashover (usually occurs at high voltage and high speed) electricity has found a path to earth normally leading to a carbon score of a field winding or amature of the motor. The result is the earth fault relay will operate and cut power immediately also the wheel slip relay will operate owing to a current difference between the motors and again cut the power. In this case the motor must be isolated by opening the isolation links.

 

Traction motor flashovers cause permanent damage and if the insulation is defeated repairs are very expensive!

 

im sure ill have made mistakes in explaining the above so am happy to be corrected

 

 

 

 

 

 

 

 

 

 

 

[ZiderHead]

Thanks pheaton, thats exactly the kind of thing I'm looking for

 

Interesting that wheelslip only seems to be detected on the outer axles of each bogie. 

[pheaton]

bear in mind ziderhead, a class 60 however uses sepex (separate excitation) in the diagrams i have shown all motors are excited at the same time, therefore when a slip occurs power is cut to all motors, not good especially if your starting a very heavy train, so a class 60 uses sepex and a microprocessor to monitor each motor, when a slip occurs or it thinks one is about to occur the microprocessor deals with the motor/motors that are slipping and rather then cut power it can change the excitation level of each motor individually on the fly, as a result the train can keep moving and theres negliable loss of power.

 

very sophisticated but not a match for the super series creep control fitted to class 59s which are able to out-haul a 60

[Gary H]

Interesting that wheelslip only seems to be detected on the outer axles of each bogie. 

 

These are the axles, especially the lead axle in the direction of travel that will slip first. (not always the case but more offten than not) A locomotive bogie will sqaut down at its rear when starting a heavy train, much like a car will when you excellerate from a stand. It is ofcourse much less noticable on a locomotive but it does happen. This action will unload the lead axle and make it susceptable to slip. I believe EMD and GE developed a weight transfer system on its locomtoives where by this weight transfer is re distributed from the trailing axle to the lead axle, very clever stuff!!

[ZiderHead]

ahhh that makes perfect sense, Ive been pondering why the middle axle would be less likely to slip. 

 

those AC4400s are beasts, nice vid. I suspect route availability might be a slight problem for them on a lot of the UK network at 33 tonnes/axle though ... 

[Gary H]

ahhh that makes perfect sense, Ive been pondering why the middle axle would be less likely to slip. 

 

those AC4400s are beasts, nice vid. I suspect route availability might be a slight problem for them on a lot of the UK network at 33 tonnes/axle though ... 

Yeah, you'd certainly have some broken rails and fishplates with those monsters over here!!

[Torr Giffard LSWR 1951-71]

Aft'noon ZH,

 

Class 47s had one of two traction motor wiring arrangements: the passenger locos e.g. 47/4 etc had parallel wired motors whilst the freight 47s e.g. 47/3 had series-parallel wired motors. The former gave faster acceleration from a standing start whereas the latter gave much better torque at low speed.

 

Cheers

 

Dave

[newbryford]

very sophisticated but not a match for the super series creep control fitted to class 59s which are able to out-haul a 60

 

So why did a 60 come out better in the trials against a 59 on iron ore trains in South Wales?

 

Recent history is of the 59's being trialled on the LBT coal trains. Last time I was there it was pretty much a 60 duty.............

 

Cheers,

Mick

[Torr Giffard LSWR 1951-71]

Hi Mick,

 

I was the driver on the Peak Forest - Bletchley workings when the Derby test centre engineers were preparing the 33056 series drivers manual for the then new locos. The conversations that we had and the tests which they undertook during the 4 or 5 trips that week (60011 and 27 loaded 102t hoppers unassisted from a standing start on a 1 in 100 climbing grade) certainly gave me the impression that they were the ultimate heavy freight loco. Their drawback was high building and maintenance costs. 

 

Cheers

 

Dave    

[Gary H]

So why did a 60 come out better in the trials against a 59 on iron ore trains in South Wales?

 

Recent history is of the 59's being trialled on the LBT coal trains. Last time I was there it was pretty much a 60 duty.............

 

Cheers,

Mick

Here we go again, U.S and Canadian versus Brit built!

I wouldn't mind a quid for every time Ive heard this yarn!

[Torr Giffard LSWR 1951-71]

Hi Gary,

 

....it may be that each has its strengths and there is some room for personal preference as a result. I didn't drive 59s so can't comment on their relative advantages.

 

Cheers

 

Dave

[Gary H]

Hi Gary,

 

....it may be that each has its strengths and there is some room for personal preference as a result. I didn't drive 59s so can't comment on their relative advantages.

 

Cheers

 

Dave

Indeed, I agree, Dave.  Personally I doubt you'd get a fag paper between the two.

On paper the 59 has the higher starting TE figure which would suggest it could start the heavier train but its all rather subjective.

A few years ago I was E.S-ing a ballast train on the Gunnislake branch in Devon. The driver that worked the train down from Westbury that night was an old school driver who started out of Paddington driving 1000's and the like!

He also had a stint working aggregate out of Merehead. He said once took 3200 tons up Savernake bank with a 59, he reckoned he wouldn't have made it with a 60.

But there you go, you may get another driver that would say the opposite.

 

Edited to say that the following night where we would be running ballast again, he said he would try and wangle it with control to get a 59 for the night, unfortunately it didnt happen and we ended up with the usual 66.

A few months after that, a non crank collegue of mine had a 59 for the night on another  ballast up Hemmerdon bank, was i envious much??!! Gutted!