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Traction motors

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Posted by Pneudyne on Friday, August 12, 2022 1:33 AM

In terms of the development of DC traction motors for use in rectifier-type electric locomotives, there was some divergence between North American and European practices in the early days.

 

In the US, the use of standard mass production diesel-electric DC traction motors was favoured, for very logical reasons as stated by GE:

 

“Because of the relatively small quantity of rectifier locomotives involved, the most economical application of a d-e traction motor on rectified single-phase 25-cycle power is one that employs a standard production-type motor with sufficient series reactors to limit the ripple properly. Motors possessing inherent load characteristics which permit the use of a reactor that saturates with load have definite advantages for such applications. A further development that would benefit this type of power transformation includes d-e motor operation on rectified 60-cycle power.”

 

That was from a 1955 AIEE paper, “Considerations in Applying D-C Traction Motors on Rectified Single-Phase Power”, by M. Simon (GE).

 

That was really a continuation of an approach that GE had adopted for its immediate post-WWII motor-generator locomotives.  For both the GN W1 and the VGN EL2b, the design basis was the use of the standard GE746 motor, originally developed for diesel-electric applications.  Westinghouse used its standard diesel-electric motor for the PRR E3b and E2c prototypes.  And then GE used its standard GE752 for its 1950s and 1960s rectifier locomotives.

 

The European situation was different though.  When production of rectifier locomotives started in the 1950s, there was no established mass production of diesel-electric traction motors.  But not only that, much larger traction motors, say 1000 hp and upwards, were required for the rectifier electric locomotives than were appropriate for the diesel-electric locomotives of the time.  Large DC motors were built for use on 1.5 kV and 3 kV DC electric locomotives, but even 1.5 kV was considered a higher than optimum voltage.  Thus there was the opportunity to design DC motors around the specific needs of rectifier locomotives.  One feature of such motors was their ability to tolerate a reasonable amount of ripple in the DC current supply, thus reducing the required amount of smoothing following rectification.

 

A brief summary of that type of motor was provided by F. Nouvion of SNCF writing in the 1967 “French Railway Techniques Catalogue”:

 

“The traction motor is not a d.c. but a ripple current type.  It has to be designed specifically for this, moreover a smoothing reactor, in which flows the traction current, is necessary to restrict the ripple.  Of course, we can do without this, and leave the traction motor to absorb the totality of the ripple.  But then the motor in its operation and technology is very close to the single phase commutator type motor, of which it then offers the drawbacks, including the impossibility of being able to employ field weakening.”

 

From that one might deduce that the “ripple current” motor lies along a vector between the conventional DC type at one end and the single-phase commutator type at the other, perhaps a little closer to the former.  As I understand it, one often found feature of ripple current motors was the use of laminated interpoles.

 

The ripple current motor did eventually find its way into American practice, for example in the Amtrak AEM7.  I have also seen one reference where the GE780 was described as a ripple current motor, but I have not been able to corroborate that from a GE source.

 

 

Cheers,

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Posted by Pneudyne on Wednesday, July 6, 2022 11:35 PM

I have found a couple of (somewhat overlapping) papers that each provide a brief commentary on the problems that beset the SNCF CC14000 locomotives.  Surprisingly, it was the seemingly simple three-phase traction motors that were the locus of difficulties.

 

The papers are:

 

IEEE paper GID83-3; 1983 April; “Three-Phase Motors in Electric Rail Traction”; Fernand F. Nouvion.

 

IME paper 28/87, 1986 October; “Considerations on the use of D.C. and Three-Phase Traction Motors and Transmission System in the Context of Motive Power Development”; F.F. Nouvion.

 

From the first paper:

 

“With this industrial frequency system [Valenciennes- Thionville], France put into service 20 CoCoI locomotives in 1956 with three-phase cage motors. Speed variation was obtained by a rotating frequency convertor varying from 0 to 135 Hz. This was a cumbersome solution which limited the use of these locomotives to freight service at a maximum speed of 60 km/h but which had total flexibility in the speed range due to the progressive variation of frequency. The results in service were disappointing for the following two reasons.

 

“1) The traction motors operated in parallel with a common supply, and the distribution of current between the motors on starting was very bad due to the steep character of the effort/speed curve of the motors and the slight electrical differences between the motor circuits themselves. In fact, on average four motors out of six really took part in difficult starting situations.

 

“2) In addition, the behavior of the cage motors was not satisfactory and expansion of the bars connected to the short circuit ring caused numerous winding breakages. In spite of an apparent simplicity, the asynchronous motor presents difficulties in manufacture, particularly for the rotor, and one can ask if the partisans of the asynchronous motor do not overdimension in power so that in service the motors ‘only heat up slightly.’”

 

 

And from the second:

 

“The squirrel-cage asynchronous motor is renowned for its robustness. Is this justified?

 

“In France, twenty 2400 h.p. CC locomotives equipped with motors of this type, supplied at variable frequency by rotary convertor groups, were put into service in 1956. These locomotives did not give the results anticipated, most especially with regard to their motors. They were progressively withdrawn in the 1970s after running a total mileage of 32 million km for the series.

 

“Locomotives with a similar mechanical structure but equipped with d.c. motors of lower power output that were put into service in 1955 are still running and carrying out the same duties as the squirrel-cage motored locomotives.

 

“With the former locomotives in service we have seen windings destroyed as a result of differential expansion in the rotor (the windings themselves and short-circuit rings) and found it impossible to parallel the motors on the same supply as a result of the poor sharing of motor currents due to constructional tolerances in the motors and differences in wheel diameter, even when the latter were small.

 

“It is indisputable that if we wish to make the maximum possible use of available adhesion, irrespective of the type of traction motor, there must be an individual and controllable supply to each motor. This is hardly an incentive to provide a multiplicity of motors on a locomotive.”

 

 

Evidently this experience was one of the factors that informed the Nouvion/SNCF leaning towards synchronous rather than asynchronous three-phase motors.

 

Both papers provide a good treatment of both the asynchronous and synchronous approaches as they stood in the 1980s.

 

 

Cheers,

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Posted by Pneudyne on Tuesday, July 5, 2022 5:12 PM

If nothing else, the CC14000 provided SNCF with some early experience with variable frequency three-phase traction motors, and may well have established them as a desideratum to be implemented as soon as suitable conversion technology became available.  SNCF’s early experience with on-board inversion, albeit at fixed frequency and single-phase, would have been with its AC locomotives equipped for regeneration, and using excitron rectifiers.

 

Relative power distribution through the two conversion pathways for the CC14000 was quite interesting.  At full power, the AC pathway, essentially all-electric, stayed at around 2000 kW across the speed range.  The DC pathway, involving two mechanical transfers, started at close to negative 2000 kW at zero speed, crossing the zero power line at around 22-23 km/h, and increasing to 3000 kW at full speed.

 

Traction motor weights given for the CC14000 and CC14100 were the same, at 1950 kg.  So the higher power-to-weight ratio advantage of the AC motor advantage was quite apparent.

 

In my June 22 posting, I quoted some comparative motor sizes and weights from an SBB paper.  The latter also included a three-phase motor, whose details I did not then quote, but which were:

 

Three-Phase Motor (1200 kW)

 

4 poles

Armature diameter 580 mm

Weight 3000 kg

 

To recap, the DC motor (1200 kW) details were:

 

8 poles

Armature diameter 760 mm

Weight 3640 kg

 

 

Cheers,

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Posted by M636C on Monday, July 4, 2022 12:37 AM

There was a proposal to convert one CC14000 to use static conversion, but this was stillborn. The CC14000 fleet was all out of service by the end of 1981. The CC14100 fleet lasted until the mid/late 1990s.

-Pneudyne

There was actually a trial carried out in the mid 1970s using CC 14003, coupled to a retired electric parcels van Z4212 which was fitted with an experimental 600kVA inverter, based on a surplus rectifier removed from scrapped experimental locomotive BB 20006 (which started out as BB 8051 on the original 50Hz test section), but which was used as a technology test bed for several years.

(Defrance, page 658)

Of course, a CC 14000 had a continuous rating at one hour of 2640 kW, so it was a limited test, but encouraged future work and cost little, using available equipment.

A similar trial had been carried out in 1971 using another of the original prototype locomotives CC 20002, (originally CC 6052) in which a full set of DC chopper controls was fitted, and used to feed the DC motors of BB 9252. This equipment later appeared in BB 7200 and BB 25200 class locomotives.

(Defrance, pages 30-33)

It appears that the CC 14000 were withdrawn before inverter technology reached a practical stage to allow conversion to the new technology. However, by the time inverters were in use, there were few tasks requiring the slow drag freight tasks performed by the CC 14000 and CC 14100.

Defrance does provide tractive effort/speed curves for CC 14000 and CC 14100 types. While the CC 1410 diagram is typical of DC traction, the CC 14000 provided 50% more tractive effort at maximum speed (only 60km/h ~35 mph). Down at 10km/h, running full current on the dc to 3 phase converter (3000amps) a tractive effort of 50 000 daN was available compared to a continuous rating of 22 000 daN on the CC 14100.

This is of course similar to the ratings seen now with AC traction compared to DC traction, but the CC 14000 could not be relied upon to provide such performance on a day to day basis, and needed attention from technicians who understood the relatively complex converters.

Peter

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Posted by Pneudyne on Sunday, July 3, 2022 5:51 PM

 

There was a proposal to convert one CC14000 to use static conversion, but this was stillborn.  The CC14000 fleet was all out of service by the end of 1981.  The CC14100 fleet lasted until the mid/late 1990s.

 

The CC14000 was viewed as being a somewhat delicate machine, not so much in respect of its equipment per se, but in terms of the proper adjustment thereof.  On the other hand, when working properly, it had good performance, with much better regenerative braking than the CC14100, which was otherwise seen as robust.

 

The CC14000 could be seen as the final development of the phase-converter locomotive using electro-mechanical equipment.  Preceding it was the Ganz-Kando locomotive built for the Hungarian Railways as its V55 class .  In terms of conversion equipment, this effectively had parallel AC-AC and mechanical power transmission paths.  An AC synchronous motor that also served as a single-phase-to-three-phase converter drove a rotary transformer of the pole-changing type, whose output provide five frequency steps from 25 to 125 Hz.  Given the stepped nature of the conversion, it had slip-ring induction motors, with the rotor windings connected to a liquid rheostat.  Apparently, it did not work all that well, and Hungarian Railways reverted to the motor-generator type, built until c.1962.

 

In the CC14000, effectively the AC-DC-AC path replaced the mechanical path, so that there were AC-AC and AC-DC-AC paths in parallel.  Here the rotary transformer was driven by a DC motor, and so had continuously variable speed.

 

In both the V55 and CC14000 cases, there was a voltage tie between catenary and motors, something not available in motor-generator locomotives.  Whether this had any practical significance I do not know, but at the utility level it seems to have been desirable.  For example, I understand that back in the era when industrial 25-to-60 Hz conversion was done in the USA, synchronous/induction rotary transformers, which provided a voltage tie, were preferred over motor-alternator sets, which did not.  And I think that later practice with 50-to-16 Hz conversion for railway purposes in Europe favoured synchronous/induction combinations over motor-alternators.  That in turn led to the slight frequency shift to 16.7 Hz for best operation of the synchronous/induction combinations.

 

The CC14100 motor-generator type was unusual in one respect, in that its traction motors each had two field windings, one being the regular series type and the other being separately and variably excited, fed from small exciters on the main conversion machines.  The separate field winding was in opposition to the series winding, and so provided a means of field weakening by increasing its excitation level.  This was the Alsthom “Anti-Shunt” system, previously used on some diesel-electric locomotives, and described in the journal “Diesel Railway Traction” for 1953, pp.109,110.  One might say that the Alsthom traction motors involved were an early example of (partial) sepex.

 

 

Cheers,

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Posted by daveklepper on Sunday, July 3, 2022 7:23 AM

I wonder if any of these rotary-converter locomotives are still in operation today.  Have any been coverted  from rotary-converter to solki-state-converter?

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Posted by M636C on Sunday, July 3, 2022 2:40 AM

Pneudyne
 
M636C
I found this French Documentary, with an english commentary that deals with early French 50 Hz electrification. Sadly the colour is quite faded but it gives an excellent view of the operation of both steam and electric locomotives.
 

 

Interesting video! 

The four locomotive types, BB12000, BB13000, CC14000 and CC14100, including their traction motors and traction motor mountings were fully described in a French language book: 

Pascal Dumont

Les Locomotives Electriques Monophases de l’Artere Nord-Est

Les Editions du Cabri; 1994

ISBN 2-908816-15-6

 

This has more technical content than is usual for railfan books.

 

Brief descriptions of the CC14000 and CC14100 types were provided in this book: 

A.T. Dover

Electric Traction

Fourth Edition

Pitman, 1963

(No SBN, ISBN or LCC)

 

The fourth edition has an additional chapter (XXVII), “Single-Phase Traction at 50 c/s” in which the CC14000 and CC14100 are covered.  The CC14000 was something of a tour-de-force, with rotary equipment that converted the incoming 50 Hz single-phase to a three-phase output varying from 0 to 135 Hz (and 0 to 1350 volts in concert) for feeding six squirrel cage three-phase traction motors.  The CC14100, of the motor-generator type, broadly followed the precepts established by GE with the GN W-1 and VGN EL-2b classes. 

The book – and this I think applies to the earlier editions as well – has detailed chapters on DC, single-phase and three-phase motors, as well as control systems, etc.  In this context, the three-phase motors chapter refers not to the modern type that arrived with inverter drives, but rather to those used in earlier times on three-phase electrified railways (such as the extensive 3.6 kV, 16⅔ Hz system that once existed in northern Italy), and those used single-phase locomotives fitted with rotary phase conversion equipment.  Control of these involved a selection from pole-changing, phase-changing, transition between cascade and parallel connections, and the use of bulk liquid rheostats.

 

The four SNCF locomotive types at interest were also described (English language) in IEE paper #1662 of 1954, “Electric Locomotives on the Valenciennes-Thionville Line”, by F. Nouvion.  This contained diagrams, schematics and comparative data.  There was also a companion paper, IEE #1661, “Electric Traction Using 50-c/s Current”, by M. Garreau.  An AIEE paper, #60-602 of 1960, “French Technical Advances in the Field of Railroad Electrification”, by F. Nouvion, focussed on the ignitron and excitron rectifier locomotives, BB12000 and later. 

 

Cheers,

 

My favoured reference for earlier French electric locomotives is:

Le Materiel Moteur de la SNCF by Jacques Defrance

I have the fourth edition from 1977, published by Editions La Vie du Rail. It is a soft bound book of 670 pages with extensive tabulations of technical data, small outline diagrams of locomotives and railcars and some unusual diagrams with simplified symbolic representations of the locomotive's internal equipment. These provide an indication of what types of equipment are fitted in a locomotive and, to some extent its location. These are particularly interesting where the same basic type of locomotive is fitted with AC or DC equipment or both....

As an example, there is the BB9200 (DC) and BB16000 (AC). The dual voltage version is the BB 25200 (the sum of the other two classes).

But it also includes tractive effort and speed diagrams, tabulations of traction motor characteristics, and quite a lot of historical information.

One feature of the symbolic diagrams is the ability to compare the equipment of the classes we have discussed earlier, the CC14000 and the CC14100. These show that while the DC traction 14100 has a single motor generator set converting single phase AC to DC, the CC14000 has two separate motor generators, one converting sngle phase AC to DC and another converting DC to three phase AC.

This is exactly equivalent to present solid state inverter systems where a DC intermediate stage is required, and allows the AC motors to be fed by variable frequency three phase AC.

Peter

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Posted by Pneudyne on Friday, July 1, 2022 6:13 PM

Referring to the original request by Enzoamps, the following may have some utility:

 

http://www.traction-electrique.ch/documents/SummarET.pdf

 

It is an online summary of the book “Traction Electrique”.  It does provide some basics for the various types of traction motors, and is reasonably recent (2012).  The translation from the original Swiss-French is at times idiosyncratic, but not an impediment.

 

 

Cheers,

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Posted by Overmod on Thursday, June 30, 2022 7:54 PM

Here's the Google PDF of the '209 patent:

https://patentimages.storage.googleapis.com/14/ee/53/ad6b803e3a309e/US2230209.pdf

For those who wish to spend an idle hour with the fascinating things James Blunt developed, go here:

https://scholar.google.com/citations?user=5qNZF1sAAAAJ&hl=en

Note that when you click on the individual items, you have a link directly to the Google API copy of the patent at upper right.

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Posted by Overmod on Thursday, June 30, 2022 7:53 PM

Here's the Google PDF of the '209 patent:

https://patentimages.storage.googleapis.com/14/ee/53/ad6b803e3a309e/US2230209.pdf

For those who wish to spend an idle hour with the fascinating things James Blunt developed, go here:

https://scholar.google.com/citations?user=5qNZF1sAAAAJ&hl=en

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Posted by Pneudyne on Thursday, June 30, 2022 6:53 PM

It may also be noted that single-phase traction motors were necessarily relatively low voltage machines, this to keep the transformer EMF and its deleterious effects (commutator sparking) within bounds at starting and lower speeds.  The restriction on voltage was greater with increasing frequency.

 

16 Hz motors typically had rated voltages of 400 volts or so.

 

25 Hz motors of conventional construction were often around 230 volts, give or take.  With the use of resistance leads, that increased to around 330 volts.

 

50 Hz motors were a more difficult case.  If conventional construction were used, then a voltage around 130 volts would be required, which was really too low, as it required exceptionally high currents.  In practice it appears that either resistance leads were used, or a duplex lap winding for the armature, each allowing a rated voltage of around 230 volts.

 

Single-phase motors though could operate on much higher voltages at higher rotational speeds.  The higher voltages were easily provided by overvoltage taps on the transformer.  This facility accounted for the prodigious short-term ratings of single-phase motors and their associated locomotives.  As an example, the numbers for the PRR E2b class were 2500 hp continuous, briefly 5200 hp at 33 mile/h at the end of the accelerating period, and short-term 4240 hp at 41.5 mile/h on ruling grades. (1, 2)

 

With conventional DC locomotives, with resistance and motor grouping control, “overvoltage” was not possible, and it was usually desirable to have a relatively low rated speed in the full-field, parallel situation.  Thus significant field weakening was required to allow full power at higher speeds.  Some large European DC motors had fields that were tapped and/or shunted down towards 20% field, and as a consequence required the use of compensating windings.  At constant voltage a DC traction motor more-or-less follows an inverse square curve.  Progressive field weakening provided a stepwise rough approximation to a constant-power hyperbola.  A corollary is that by operating back up the inverse square curve, higher than rated power was available at lower than rated speed.  Numbers on hand for the CUT 3 kV DC locomotives are 2635 hp full field and weak field continuous, and 3030 hp full field one-hour.  But in service, brief peaks of 6000 hp at the rail were observed, with 4000 to 5000 hp at the rail for longer periods. (3)

 

Motor-generator locomotives were limited by the capacity of the motor-generator unit, so typically had but modest overload capacity.  As an example, the GN W-1 class could get to 5800 hp at the rail, as compared with 5000 hp rated. (4)

 

Rectifier locomotives had the same potential for the use of overvoltage transformer tappings as the single-phase type, but in the early years at least, this seemed not be utilized to any great extent, probably in deference to rectifier well-being.

 

DC motors could be built to operate on 1.5 kV, perhaps a little more towards 2 kV, although 1.5 kV was the highest required in practice for conventional DC locomotives.  For 3 kV systems, the motors could be insulated for that voltage, but could not operate on it.  Rather it was also necessary to have always at least two motors in series across the supply.  Insulation for 3 kV DC was not without its penalties, though.  The required thicker insulating layers and larger air gaps made for larger and less efficient motors.  Within a given motor size constraint, for example as required for truck mounting, power was limited as compared to the 1.5 kV DC case.  When SNCF was looking for improvement over its existing 1.5 kV DC system, it did look at 3 kV DC, but rejected it because whereas a four-motor 1.5 kV DC locomotive with the largest feasible motors would meet its high-speed haulage requirements, a six-motor 3 kV locomotive would not. (5)  25 kV, 50 Hz AC was of course the answer.

 

 

(1)   Railway Gazette; 1952 April 18; p.432ff; “New Electric Freight Locomotives for the Pennsylvania”.

(2)   Railway Mechanical Engineer; 1952 February; p.89ff; F.D. Gowans, B.A. Widell &  A. Bredenberg; “Series A.C. Electric Locomotives with Dynamic Braking”.

(3)   AIEE Paper 33-36; 1933 January; F.H. Craton & F.W. Pinkerton; “Operation of 3,000-Volt Locomotives on the Cleveland Union Terminals Electrification”.

(4)   ASME Paper 49-SA-7; 1949 June: J.C. fox, J.F.N Gaynor & F.D. Gowans; “Motor-Generator Locomotives. Their Design and Operating Characteristics”.

(5)   AIEE Paper 60-602; 1960 April: F. Nouvion; “French Technical Advances in the Field of Railroad Electrification”.

 

 

The ASME paper was a full treatment, with tripartite authorship (GE, GN and VGN) of the GN W-1 and VGN EL-2b locomotives.  Both were predicated on the use of the GE746 traction motor (a standard diesel-electric type at the time) with designs then developed to meet the respective GN and VGN requirements.  It is an interesting read.

 

The AIEE paper also includes some commentary on the 2-C+C-2 running gear lateral controls.  One has the impression, that in its own field, GE was pursuing a pathway that had some parallels with what J.G. Blunt of Alco was doing with steam locomotive running lateral controls.  (In that case there had been stepwise progression to the final ”lever principle” form, first seen on the UP FEF-2 of 1939 and described in US patent 2230209 of 1941 January 28.  An interesting point is that the “shape” of the pilot truck lateral control curves were essentially opposite for the electric and steam locomotive cases.

 

 

Cheers,

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Posted by Pneudyne on Monday, June 27, 2022 8:03 PM
M636C
I found this French Documentary, with an english commentary that deals with early French 50 Hz electrification. Sadly the colour is quite faded but it gives an excellent view of the operation of both steam and electric locomotives.

 

Interesting video! 

The four locomotive types, BB12000, BB13000, CC14000 and CC14100, including their traction motors and traction motor mountings were fully described in a French language book: 

Pascal Dumont

Les Locomotives Electriques Monophases de l’Artere Nord-Est

Les Editions du Cabri; 1994

ISBN 2-908816-15-6

 

This has more technical content than is usual for railfan books.

 

Brief descriptions of the CC14000 and CC14100 types were provided in this book: 

A.T. Dover

Electric Traction

Fourth Edition

Pitman, 1963

(No SBN, ISBN or LCC)

 

The fourth edition has an additional chapter (XXVII), “Single-Phase Traction at 50 c/s” in which the CC14000 and CC14100 are covered.  The CC14000 was something of a tour-de-force, with rotary equipment that converted the incoming 50 Hz single-phase to a three-phase output varying from 0 to 135 Hz (and 0 to 1350 volts in concert) for feeding six squirrel cage three-phase traction motors.  The CC14100, of the motor-generator type, broadly followed the precepts established by GE with the GN W-1 and VGN EL-2b classes. 

The book – and this I think applies to the earlier editions as well – has detailed chapters on DC, single-phase and three-phase motors, as well as control systems, etc.  In this context, the three-phase motors chapter refers not to the modern type that arrived with inverter drives, but rather to those used in earlier times on three-phase electrified railways (such as the extensive 3.6 kV, 16⅔ Hz system that once existed in northern Italy), and those used single-phase locomotives fitted with rotary phase conversion equipment.  Control of these involved a selection from pole-changing, phase-changing, transition between cascade and parallel connections, and the use of bulk liquid rheostats.

 

The four SNCF locomotive types at interest were also described (English language) in IEE paper #1662 of 1954, “Electric Locomotives on the Valenciennes-Thionville Line”, by F. Nouvion.  This contained diagrams, schematics and comparative data.  There was also a companion paper, IEE #1661, “Electric Traction Using 50-c/s Current”, by M. Garreau.  An AIEE paper, #60-602 of 1960, “French Technical Advances in the Field of Railroad Electrification”, by F. Nouvion, focussed on the ignitron and excitron rectifier locomotives, BB12000 and later. 

 

Cheers,

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Posted by JayBee on Sunday, June 26, 2022 2:37 PM

I would like to add that the newest French TGV powercars do use permanent magnet AC traaction motors.

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Posted by Pneudyne on Saturday, June 25, 2022 5:53 PM

daveklepper

 

A parallel development in DC traction for light-ral, rapid-transit, and MU cars, but unknown to me for locomotive applications, was chopper control.

 

 

 

Chopper control was used for DC locomotives.  As far as I know, aside from experimental units, the first series-produced type was the SNCB, Belgium 20 class of 1975, for its 3 kV DC system.  These were six-motor units (C-C) with sepex motors.  Other major 3 kV DC systems who used chopper locmotives included FS, Italy and SAR, South Africa.  The interval between the advent of chopper controls and the arrival of inverter/AC motor techniques seems to have been relatively short as technology epochs go.

 

 

Cheers,

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Posted by Pneudyne on Saturday, June 25, 2022 5:50 PM

bogie_engineer

 

Pneudyne,

Great to see you posting here, always enjoy reading your well researched and informative posts on that other RR forum.

Dave

 

 

Hi Dave, thanks very much for the welcome and the kind words.  There are some very interesting thread topics active here!

 

 

Cheers,

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Posted by bogie_engineer on Wednesday, June 22, 2022 9:58 AM

Pneudyne,

Great to see you posting here, always enjoy reading your well researched and informative posts on that other RR forum.

Dave

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Posted by jeffhergert on Wednesday, June 22, 2022 9:51 AM

timz

 

 
daveklepper
Transition was no longer required , at least in many cases, when three-phase alternators replaced  DC genrators, even while retaining DC motors.

 

To clarify: all EMD and GE C-Cs had transition until ... guess the SD50 was the first one to try to do without it?

 

 

The SD70m still make transition.  Ours around 25 and 40 mph.  I've noticed foriegn power sometimes have a different setting, a few mph difference.

That way going up a stiff grade with them down on their knees you get to feel the lunge, has they momentarily drop the load and then start pulling again, twice.  All the time hoping it doesn't break a knuckle or yank out a drawbar.  

Jeff

 

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Posted by Overmod on Wednesday, June 22, 2022 9:14 AM

It's always nice to get good information from actual experts in a technology.  We're fortunate to have them actively posting here.

M636C
One of the reasons quoted for the change was greater fuel economy, but I don't understand why changing an alternator would save fuel, at least, not on its own...

I suspect this had to do with better control of the field so that the Woodward governor could be commanded to make better power at a lower nominal notch.    

I was disappointed that nobody commented on my earlier post about directly fed 50Hz motors.  The demonstration model in the video suggested that the motors were larger in diameter than the driving wheels, and were located well up in the bogie structure.

You'd have to use 'monomoteur' or body-mounted motors -- and these are certainly a 'thing' -- but you'd need additional room in the carbody for the motors and associated support.  American practice has generally used some variant of wheelbarrow suspension with the smaller wheel sizes.

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Posted by Pneudyne on Wednesday, June 22, 2022 1:41 AM

50 Hz single-phase traction motors were certainly larger than their low-frequency counterparts, which in turn were larger than the DC types.  As compared with low-frequency motors, the required lower flux density (to manage the transformer EMF problem) meant more poles and so larger commutators, etc.

Here are some comparative numbers from a 1977 SBB (Switzerland) paper, for nominally 1200 kW motors:

 

DC Motor:

 

8 poles

Armature diameter 760 mm

Weight 3640 kg

 

Single-Phase 16 Hz motor:

 

10 poles

Armature diameter 820 mm

Weight 3860 kg

 

Single-Phase 50 Hz motor:

 

20 poles

Armature diameter 990 mm

Weight 4600 kg

Power 1050 kW

 

Note that even with its larger armature diameter, the 50 Hz motor is of lower power (1050 kW) than the others.  Presumably a 1200 kW 50 HZ motor would have been too large.

 

 

Re the SNCF (France) BB12000 (DC motors) and BB13000 (50 Hz motors) types, the diagrams on hand show that the BB13000 motors, at around 1215 mm outside diameter, whereas the BB12000 motors were around 820 mm diameter.  In both cases the driving wheel diameter was 1250 mm.

 

The 50 Hz motors of the BB12000 were to an ACEC (Belgium) design.  ACEC was a Westinghouse licensee, and for its 50 Hz motors (initially built for use in the Congo), it chose the resistance lead approach that Westinghouse had adopted for its 25 Hz motors post-WWII.  Actually it was an old idea that although discarded early on, was thought to be workable with modern, more heat-resistant materials and techniques.  Such motors were used for some EMUs of the time, and were originally specified for the PRR prototype locomotives, before Westinghouse requested the change to using Ignitron rectifiers and DC motors.  GE was on the record as being antithetical to the resistance lead technique, and stayed with improved conventional techniques for its late 25 Hz motors.

 

The 50 Hz motor was a quickly passing phase, last used for new locomotives c.1958, and for EMUs a couple or so years after that.  Notwithstanding the difficulties associated with mercury arc rectifiers in the traction environment, on balance they seemed to have been preferred over 50 Hz motors.  Also, towards the end of the 1950s, the near term promise of solid-state rectifiers – and the possibility of converting existing locomotives from mercury arc to solid-state, would also have swayed choices.  One potential advantage of single-phase motors was that regenerative braking, if required was relatively easy to do.  But very few 50 Hz motor locomotives were so-fitted.  (Whereas it was more-or-less standard for the SBB 16 Hz fleet.)  It would have been difficult to do regenerative braking with ignitron-type rectifiers, but SNCF did it with the excitron type, and I think continued to build excitron regenerative locomotives after moving over to silicon rectifiers for its non-regenerative requirements.  Of course, rheostatic (dynamic) braking could be done with equal ease for both single-phase and DC motors.

 

 

Cheers,

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Posted by daveklepper on Thursday, May 19, 2022 4:14 AM

MS:  I didn't comment because such large 50Hz commutator motors are entirely new foir me.  At the MIT EE Department, 1949 - 1957, EMD Summer 1952, they were considered impracticaql, except in small applications, such as Lionel and Gilbert American Flyer.   This  is now old technology, but new for me.

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Posted by M636C on Thursday, May 19, 2022 12:15 AM

Erik_Mag

Dunno about theGEC-Cs, but the later EMDs used alternator transition instead of traction motor transition.

There could be some benefit from using AC motor transition, connecting two windings in series at low speeds and in parallel at high speeds. This would ease component requirements for the inverters.

 

The change from using traction motor groupings was required by EMD's adoption of Super Series wheel slip control. It always amused me that "Super Series" required that all motors be in parallel, but that arrangement allowed single motors to be isolated when they slipped, rather than cutting power to all motors when an axle slipped. The "Series"name referred to series wound motors. I understand that ASEA was involved in the development and they had a system which was used with separately excited motors.

In the cab of the lead unit with conventional wheelslip control with 37 000 long tons on the drawbar, you could tell when the power cut on a trailing unit long before the remote wheelslip bell rang. I never rode on such a train after they started using SD50s but I'm sure they worked better than the old Alcos.

I recall reading in material from the time of the introduction of Super Series that GE had been using internal switching in alternators before EMD introduced the AR11 to replace the AR16. One of the reasons quoted for the change was greater fuel economy, but I don't understand why changing an alternator would save fuel, at least, not on its own...

I was disappointed that nobody commented on my earlier post about directly fed 50Hz motors.  The demonstration model in the video suggested that the motors were larger in diameter than the driving wheels, and were located well up in the bogie structure. I wonder if larger diameter commutators would reduce the chance of flashover with a high frequency AC current.

Peter

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Posted by Erik_Mag on Wednesday, May 18, 2022 4:45 PM

Dunno about theGEC-Cs, but the later EMDs used alternator transition instead of traction motor transition.

There could be some benefit from using AC motor transition, connecting two windings in series at low speeds and in parallel at high speeds. This would ease component requirements for the inverters.

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Posted by timz on Wednesday, May 18, 2022 11:25 AM

daveklepper
Transition was no longer required , at least in many cases, when three-phase alternators replaced  DC genrators, even while retaining DC motors.

To clarify: all EMD and GE C-Cs had transition until ... guess the SD50 was the first one to try to do without it?

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Posted by daveklepper on Wednesday, May 18, 2022 11:06 AM

I see a requirement to add to the discussion bof transition.  Transition was no longer required , at least in many cases, when three-phase alternators replaced  DC genrators, even while retaining DC motors.  By carefull control of field currect, the right output voltage and thus power to the motors cold be assres at the right RPM of the diesel for efficiency at the specific throttle (controller) setting and the trains speed.

A parallel development in DC traction for light-ral, rapid-transit, and MU cars, but unknown to me for locomotive applications, was chopper control.  Instead of  wasfing power in grid resistors and asdding the complexity of series-to-paralltl transition, the current from a fixed voltage source was interrupted, with the on time increasing and  the off time decreasing as more power was desired and as speed increased.  I believe the Baltimore Light Rail system still uses raii cars with this technology.

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Posted by M636C on Monday, May 16, 2022 5:16 AM

On an earlier post, the subject of directly fed AC traction motors was raised:

I found this French Documentary, with an english commentary that deals with early French 50 Hz electrification. Sadly the colour is quite faded but it gives an excellent view of the operation of both steam and electric locomotives.

In particular, it describes a class of locomotives, the BB 13000, that used 50Hz commutator motors. These locomotives were all (53 total) still in use in 1977. The majority of passenger locomotives (BB 12000) were built with ignitron rectifiers, and these were probably converted to solid state rectifiers later. Most Freight locomotives were motor generator units with DC motors (CC14100) but there were a few (CC14000) units that had three phase motors driven by rotary converters.

Anyway, this is the video:

https://www.youtube.com/watch?v=7l6v2qLYg4Q

Even dyed in the wool steam fans should enjoy this...

Peter

 

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Posted by Erik_Mag on Wednesday, May 11, 2022 10:53 PM

M636C

The actual motors can be driven by either type of inverter, so traction motors can be retained if GTO inverters are replaced by IGBT or later devices.

One issue with designing motors to be driven by inverters is dealing the with the ripple currents induced by the switching. These currents can be a pain to deal with as proximity effect rears its ugly head. One possible advantage of using SiCFET's is that it will be easier to filter the ripple currents allowing more conventional wiring to be used in the motors.

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Posted by Erik_Mag on Wednesday, May 11, 2022 10:45 PM

timz

 

daveklepper
An AC commutator motor, as used in nearly all PRR, NYNH&H, and GN electric locomotives...

Not GN.

 

FWIW, GN as using a few of the former Spokane & Inland Empire locomotives on the Cascade tunnel line and those were most assuredly using AC commutator motors. OTOH, all of the locomotives built specificaly for the new Cascade Tunnel electrification were M-G equiped with DC traction motors.

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Posted by Overmod on Wednesday, May 11, 2022 2:41 PM

The W-1s were motor-generator and used GE 746 motors; the Z-1s were motor-generator and also used DC motors.  I remember the PRR FF2s as being motor-generator too.

These motors all had 'commutators' but were not the AC 'universal' type that could operate from multiple transformer taps like the GG1s... 

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Posted by timz on Wednesday, May 11, 2022 12:30 PM

daveklepper
An AC commutator motor, as used in nearly all PRR, NYNH&H, and GN electric locomotives...

Not GN.

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