• "Hybrid" locomotive combinations

  • General discussion about locomotives, rolling stock, and equipment
General discussion about locomotives, rolling stock, and equipment

Moderator: John_Perkowski

  by D Alex
A few years ago, I was reading in Classic Trains about a special Canadian train, marking the anniversary of I believe the Canadian Pacific. It was pulled by one of their classic steam locomotives as well as a diesel B-unit. This got me to wondering; how often were such pairings done? I'm aware that the Union Pacific often mated their turbine locomotives with road-switcher diesels, but how often were other, more unusual consists done; things like diesel+electric, or even steam+electric? B-units and steam? It almost seems a marriage made in heaven, considering that steam was more efficient at speed, whereas diesels excelled at low-speed and staring from a stop. Where such combinations ever "common"?
  by Allen Hazen
Huge topic. I think it has been discussed before, but I don't remember the string title or the forum (this one? steam locomotives?). I'll startwith a few random factoids. About steam-diesel combinations: electric-diesel is another whole topic!

(1) Putting both steam and diesel locomotives on a train was common in the transition period (late 1940s/1950s). I think the combinations in that period were always "double headers" (i.e. both locomotives with crews): in the more modern period of steam excursions, people have worked out the machinery to connect a steam locomotive throttle to something that generates electrical multiple unit signals, so the engineer on the steam locomotive also controls the diesel. (I first heard about this technique in a "Trains" article of the 1970s about the Clinchfield Railroad's specials, which had an ancient 4-6-0 in m.u. with a diesel B-unit.)

(2) One of the earliest regular uses of steam/diesel combinations was on the Trans-Iranian Railway during WW II. (The Trans-Iranian was an alternative to Murmansk convoys in shipping aid from the western allies to the Soviet Union.). Steam locomotives used may have been standard War Department locomotives from the U.S.: not sure. Diesels were a CC version of Alco's RS-1 roadswitcher. And you're right about the different characteristics of steam and diesel locomotives: the operators (the Trans-Iranian was essentially taken over by the American army for the duration, and was operated by American railroaders in the Army Transportation Corps) found that using steam-diesel combinations was more efficient than either using pure steam or using pure diesel.

(3) (I said "random" factoids!) During the transition from steam to diesel, a rational railroad management would buy diesels first for the assignments where there was the most to be gained from their superior efficiency. Helper service was typically a low-mileage assignment, so (even though a diesel's low-speed advantage over steam would have made it ideal for a helper!) buying a diesel to use as a helper would mean using steam for more high-mileage jobs: wasteful. So a typical scenario would be that a passenger or freight train would be hauled by diesels until it got to the mountain: at that point a steamer would be coupled on (in front on passenger, perhaps at the rear as a pusher on freight) to help it up the hill. This was a way of life on, e.g., the Pennsylvania Railroad at Altoona, with a standardized procedure. Including such things as washing the cinders off the diesel's windshield when when the head-end helper uncoupled at the top of the hill.

I'm sure other people can add lots of details!
  by spRocket
The Milwaukee Road came up with a way to MU their "Little Joe" electrics with diesel units as well.
  by Allen Hazen
Yes, and there are photos of a Little Joe leading one or more diesel units. The only other U.S. railroad I know anything about as regards electric/diesel multiplying: apparently the E-44 electrics (built by GE in the early 1960s), but not earlier classes of PRR electric "motors", were capable of operating in multiple with diesels, but only if the electric was leading. This was discussed on one of these forums (PRR? GE?) some time back. It's not clear whether all E-44 had the relevant equipment installed, and I have never seen a photo of an E-44 operating with a diesel. (There are many photos showing steam and electric locomotives on the same train on the PRR, but this was usually if not always a matter of the steamer hauling the train and its electric locomotive through a dead wire zone.)
  by Pneudyne
As Allen has said, this is a big topic. I have made quite a few notes over the years, and will post a few comments when I am back at home. Travelling right now.

  by Allen Hazen
Travel safely! I look forward to reading your comments!
  by Pneudyne
I think that Allen has adequately covered the double-heading case, where each locomotive type was crewed. As said, in the steam-plus-diesel case during the transitional era, it was often a way to continue to use existing steam power when the diesel fleet was not yet large enough to cover all assignments. I suspect that steam locomotives were often used because they were available, and not because they were optimum for the job.

Steam-plus-electric combinations were probably a lot rarer. In general there was little point in electrifying a section of railroad and then running some steam-hauled services over it, except perhaps in abnormal circumstances. But the combination did happen. I understand that there were cases in the 1960s where British Rail used it when there was a shortage of electrically heated passenger consists, and the electric locomotives involved did not have steam heating equipment. Thus double-heading with a steam locomotive was required to enable provision of steam for car heating. I suspect that some steam-plus-diesel combinations arose for the same reason.

Apparently gas turbine (GTEL)-plus-steam combinations happened on the UP. Late in the steam era, the “big” Challengers were used as pushers on the Wahsatch grade eastbound out of Ogden. This included on trains headed by GTELs, including the GTEL8500s. The big Challengers were originally designed to operated east of Green River, taking the same trains that the Big Boys brought in from Ogden. Pushing at 15 to 20 mile/h was probably not in the original design brief. I understand that pushers were used in part to allow higher upgrade speeds. Possibly they allowed higher tonnage trains, closer to what the GTEL8500s could pull east of Evanston. The Big Boy fleet was moved to Sherman Hill in the late 1940s following initial dieselization west of Laramie. There is some evidence that at least the GTEL4500s sometimes double-headed (with GTEL leading) with the Big Boys westbound up Sherman Hill.

Whilst double-heading combinations could be happenstance, MU combinations were more likely the product of specific need and engineering thought , given the complexities and costs involved.

The steam-plus-trailing diesel MU case was/is, as far as I know, confined to excursion type operations with restored/preserved steam locomotives. The steam locomotives involved were equipped to control trailing diesels via a separate controller, portable or fixed, which was not linked to the steam locomotive throttle. Apart from the difficulties of developing a suitable interface, separate diesel control suited the nature of these operations. The trailing diesel(s) were there to provide some or all of additional power on steep upgrades, dynamic braking on steep downgrades, additional power during acceleration, and for emergency power in the event of steam locomotive failure or deficiency. Otherwise they were left in idle. I understand that the first example of a steam locomotive equipped for this purpose, with a portable diesel controller was SP 4449, as part of its 1975 restoration. As a later example, in Australia, a preserved Victorian Railways R-class 4-6-4 was fitted with a diesel control stand.

The electric-plus-trailing diesel MU case was/is not all that common. That is not surprising given that once a section of railroad is electrified, it is usually advantageous to operate as much as possible of the traffic electrically, unless specific circumstances indicate otherwise.

The Milwaukee appears to have been the first to do this. In the mid-1950s, more locomotive power was required at the head end of freights in electrified territory, in a situation where obtaining additional electric locomotives was most unlikely and in fact there were factions in favour of abandonment of the electrification entirely. On the other hand diesels to assist the electrics were readily available. Thus in 1956 electrical engineer Wylie devised his eponymous throttle that allowed both synchronized and independent control of trailing diesel locomotives from the “Little Joe” electrics. This was fitted to the fleet in 1958-59. Effectively it was a miniature diesel control panel with a detachable link between its throttle handle and the electric power control handle. With the link in place, the diesel and electric power controls were synchronized. As I understand it, the diesel control panel could also control dynamic braking in trailing diesels, but whether this could be synchronized with regenerative braking on the Little Joes I don’t know. Doing that might have been a tall order, particularly given the setup procedure typically required for regenerative braking on DC locomotives. Holley recorded that additional to the Little Joes, five of the EF-5 class freight motors were also fitted with trailing diesel MU equipment, in this case done by relays rather than via a mechanical system.

Initially the diesels were used as helpers as required behind usually paired electric locomotives, but later single electrics were used more-or-less as point helpers ahead of diesel consists that originated outside of and ran through the electric sections.

The Pennsy E44 case is a bit of a mystery. Cunningham reported that the fleet had diesel MU capability. But beyond that there does not appear to be any evidence supporting that notion. Given the extent of the Pennsy’s electrified network, and its commitment at the time to electric power, it seems less likely that regular electric-plus-diesel MU operations would have been envisaged. On the other hand, diesel MU capability might have been seen as useful in unusual situations such as short-term irregular traffic peaks.

A major example, dating from 1999 and still current, is the Cape gauge Sishen-Saldanha iron ore line in South Africa. Originally diesel operated, this was electrified at 50 kV and for a while was fully operated by electric locomotives. When in 1999 it was desired to run longer trains, more head-end power was needed, but at the time the electric fleet was insufficient, so available diesels were used behind the electric locomotive consists. These were controlled by a so-called “smart cable” system that translated the electric locomotive control protocol into diesel protocol. Later Locotrol distributed power was introduced, allowing even longer trains with mid-train and rear-end locomotive consists that were electric and diesel mixes, as far as I know with the electric locomotives as Locotrol receivers. More recently the electric locomotive fleet has been renewed and enlarged, but mixed locomotive consists are still used where the total number of locomotives required for a train exceeds the maximum number of electric locomotives that the catenary and supply system can support.

In the electric-plus-diesel context should also be mentioned the British Rail Southern Region scheme of the 1960s, which allowed interworking between EMUs, electric, diesel and electro-diesel (dual-power) locomotives, with any type able to lead. Whilst it was primarily oriented to through passenger operations that traversed both electrified and non-electrified territories, there were some freight services operated with diesel-plus-electro-diesel combinations, either leading, the latter operating under electric power over the third rail, but diesel power otherwise. The diesel locomotives involved were few in number, and specially retrofitted for the purpose. It was envisaged that the scheme would also be extended to include the DEMU fleet, but this was never realized. (I think that one DEMU set was modified accordingly, but that the modifications were not actually commissioned.)

The GTEL-plus-trailing diesel case of course applied to the UP only. By the late 1950s it was looking for substantially increased power at the head-end of its freights, and the forthcoming GTEL8500 fleet addressed that need. But the existing GTEL4500s, hitherto operated singly, were not powerful enough for the emerging era. The UP did try MU operation of GTEL4500 pairs. This was problematical in that in tunnels, the trailing unit was starved of combustion air. As an alternative, it tried GTEL-diesel MU combinations, which did work well. The development work was done in 1958, and most of the GTEL4500 fleet was subsequently fitted for such operation. By way of post facto rationalization, if one assumes that through most of the 1960s, the GTELs were more economical than diesels as power for UP fast freights, then the GTEL-plus-diesel combination retained some of that economy, at the same time allowing continued use of the GTEL4500s into an era when as individual units they were insufficiently powerful, but could not be operated in pairs. And the trailing diesel locomotives were readily available from the large pool. So it was a pragmatic move. The power requirements eventually outstripped the 8500 hp of the GTEL8500s, and most of these were also equipped for MU operation with trailing diesels, in order to build combinations of up to 15 000 hp. Even at this level, the GTEL was still majority power.

Details of the GTEL-to-diesel MU interface have not surfaced. One may assume that it included appropriate mapping from the 20-notch GTEL throttle control to the 8-notch diesel control. Probably it also included provision for field loop DB control on the diesels. Mixing field-loop and potential wire DB controls was by 1958 established practice, having been originated by F-M in 1955.

  by Pneudyne
In the original posting in this series was mentioned the use of hybrid locomotive combinations in order to obtain haulage characteristics that combined the best characteristics of the various types. I suspect that this was quite rare.

The MU examples I mentioned in the previous posting do not really fit into this kind of combination. In these cases, diesels were used with electrics and GTELs mostly because they were a readily available way of increasing locomotive consist power. That their haulage characteristics might be different was largely something to be accommodated, and in the earlier days most likely fixed mappings were used between the leading electric and GTEL control systems and those of the trailing diesels; these may have been something of a trade-off. The Wylie throttle used by Milwaukee allowed both synchronized and separate control of the trailing diesels, but I imagine that the synchronized mode was used more often. The South African Sishen-Saldanha electric-plus-diesel case might have used some form of modulated rather than fixed mapping for trailing diesel power control; its designation as a “smart cable” at least suggests that possibility.

Diesel locomotives tend to be nominally constant power machines above speeds of 10 mile/h or so. Electric locomotives are usually accelerated on a more-less constant torque basis until well into the operating speed range, perhaps beyond 30 mile/h. After that they operate closer to constant power. With manual acceleration control, the engineer might still be notching up at speeds well beyond the point where typical diesels were in Run 8. GTEL characteristics were nominally similar to those of diesels, but there were differences in the control systems that were potential complications. There was one example of what might be said to be further integration, and that was in UP’s experimental coal-burning gas turbine locomotive. The lead unit was a modified Alco PA1, fitted with a GTEL-type 20-notch throttle control, from which its own diesel engine was also controlled. (Most likely by mapping back to 8 notches, although the GE 17MG governor might have been configurable for 20 steps by using a different (and more complex) speed control resistor matrix.)

That said, the industry had a history of developing appropriate adaptations to accommodate differences in locomotive control systems and characteristics. Perhaps an order of magnitude less in severity than the hybrid combinations cases, some examples were: manual transition control of trailing locomotives from leading locomotives with automatic transition; universal dynamic brake controls that covered both the field loop and potential wire types; power matching on four-motor locomotives to enable their operation in mixed consists with six-motor locomotives, when use of the latter became widespread; mixed MU operation of diesel-hydraulic and diesel-electric locomotives.

Also worthy of inclusion here is the EMD FL9 case, where a 28-notch DC electric control system (with partial automatic acceleration) was controlled by an 8-notch diesel throttle. And before that, the integration of AC and DC control systems on dual-system New Haven electric locomotives. Both Middleton and Cunningham reported that the Virginian EL-C rectifier electrics were fitted to MU with the earlier EL-2B motor-generator units. If so, that would have been a tour-de-force, but there is no other supporting evidence. Motor-generator electrics had curves that more like those of diesel-electric locomotives.

And it may be mentioned that the still-born “ACE 3000” modern reciprocating steam locomotive project of the 1980s included provision for MU operation in mixed consists with diesels. (The idea of MU’ing steam locomotives goes back a long way, but never reached fruition although remote control of single locomotives for push-pull operations was quite common in Europe.) But that was done not so much to combine different characteristics - although that might have been an incidental benefit - but to make the new steam loocmotive more acceptable to the railroads.

  by Allen Hazen
Thanks for that very informed essay, Pneudyne!
...Why would m.u.-ing the Virginian EL-2b and and EL-C locomotives have been a "tour de force"? Both are GE designs and only about a decade apart: quite possibly some of the same GE engineers work on the control systems of both classes! And both were designed for the same service and (roughly) same speeds: the per-axle horsepower isn't very different.
  by Pneudyne
The difficulties in MU’ing the VGN EL-C and EL-2B electric locomotives stem from the fact that the former is of the rectifier type with dynamic braking, and the latter is of the motor-generator (MG) type with regenerative braking. These two types have different characteristics and different control systems, particularly so in respect of electric braking.

I don’t have specific information for the EL-2B, but on MG locomotives it was not unusual that both the power handle (controlling main generator excitation) and the braking handle (controlling excitation of the regenerative exciter, used to supply the traction motor fields) were used together for braking control, this approach allowing proper initial setup at relatively low current combined with a wide range over which the brake could be used. At any given setting the regenerative brake will tend to approach a given speed, braking if the locomotive is above that speed and motoring if below it. In some MG locomotives the regenerative connection was used for motoring at the high speed end of the range, effectively allowing field control. (One could say that it was an early example of sepex motors in traction applications.) So regenerative and dynamic braking curves, on a notch-by-notch basis, are quite different. But in the regenerative case, by appropriate manipulation of both handles as required over the speed range, a “normal” looking braking curve may be obtained.

That’s not to say that a workable interface could not have been developed, but I think it would have been quite complex and probably justified only if regular mixing of the two types were planned, which I think was not the case. In that case, it might have been easier to have the EL-2B always leading. Mapping from the EL-2B to the EL-C power controls was probably the easier part. And the EL-C dynamic brake control might have been mapped from the EL-C braking handle alone, perhaps accepting that full braking might not always be available depending upon how the EL-2B was set up – although electric braking was likely a key aspect of VGN operations.

It is possible is that the EL-C was built with a control system and characteristics that enabled it to interwork with the EL-2B. That is not apparent from any of the information I have found, which discusses only its own control system without mention of the EL-2B. But apparently it was the subject of a couple of AIEE papers, one by GE and one jointly by VGN and EE. These I imagine would be more detailed.

  by Allen Hazen
Many thanks! I was only thinking of the powered part of the use cycle, and hadn't considered the regenerative vs. dynamic braking issue, which I see WOULD complicate things...
Do you have any references to the AIEE papers? I have access to a university library, and if I'm nice to the librarians they might help me find them.
  by Pneudyne
Both papers were mentioned at the end of a Railway Gazette article on the VGN EL-C:

“The electrical system has been described in a paper to the American Institute of Electrical Engineers earlier this year by Mr. J. C. Brown, of the General Electric Company of America. Its introduction was also made the occasion of a paper submitted to the A.LE.E. Committee on Land Transportation by Mr. J. C. Fox, of the Virginian Railway, and Mr. J. P. Wiles, of the General Electric Company.”

The first of those is listed at the IEEE site, at: https://eur02.safelinks.protection.outl ... reserved=0" onclick="window.open(this.href);return false;

  by talltim
There's this http://www.douglas-self.com/MUSEUM/LOCO ... isselc.htm" onclick="window.open(this.href);return false; ...
An example from the UK, when the 225 train sets were being introducted the Class 91electric locos were ready before the coaches and DVTs (purpose built cabbages). To get them into use some HST sets were were converted by removing one power car and converting the other to use the same MU protocols as the class 91s. Originally it was planned that the power car would just provide HEP for the coaches (which was a different system to that provided by the Class 91s), but it was found that prolonged idling did not suit the power units so they were reconfigured to provide traction power as well. This gave a 8250hp,125mph train with a diesel at one end and an electric at the other. Once the rest of the sets were completed the HST sets were reformed into their original all diesel formations.
  by Pneudyne
The 91-plus-HST combination was a good example of hybrid power being used because it was, at least for an interlude, operationally convenient, and not because the combination provided optimum traction characteristics.

As far as I know, the 91 class had the BR Plessey TDM (time division multiplex) MU system, which required only two trainwires but provided the equivalent of a something like a 64-trainwire conventional system. I think it covered all likely diesel and electric control functions, including dynamic braking, so was designed from the start to accommodate hybrid power combinations. Apparently it also covered coarse as well as fine power control. Some of the associated DVTs had EMU-like four-notch power controllers, so it would appear that anywhere between that and close to continuously variable could be accommodated.

The HSTs had a conventional 36-trainwire wire MU system, with 5-notch power control. Their Paxman Valenta engines were known not to like excessive idling, and the fast idle (1000 rev/min) required when they were supplying HEP probably made that worse. I understand that NSWGR found the same with its XPT sets.

  by Pneudyne
I have since remembered that I kept a copy of the Railway Magazine 1999 December article on the BR TDM MU system.

That article did cover the adaptation of several class 43 HST power cars for use in consists with class 91 electric locomotives at the other end. Apparently the HST power controls (throttle handles) were modified to delete the notches, allowing continuously variable control of the 91s via the TDM system. I imagine this was done at the time when it was not planned to use the HST power cars for traction power. But when it was decided that they would be used for traction power, I’d guess that the on-board TDM cabinet was equipped with the facility to output an HST-speak 5-notch control protocol. I doubt that the engines were changed over to governors with continuously variable control, as that would have been a major exercise.

One may visualize the TDM system as doing with an LF (185 kHz) carrier over wires what Locotrol, dating from the second half of the 1960s, did with wireless VHF carriers. Continuously variable power control of thyristor-type AC electric locomotives was something that GEC (or rather its constituents EE and AEI) had also used since the late 1960s. It was essentially a voltage-based (potential-wire) system, but to avoid voltage-gradients along trainwires, it was transmitted by PWM (pulse-width modulation), so that was a step on the road from analogue to digital. PWM had seen prior use, as part of the internal control system in the UP GTEL-8500, which was an early use of transistor technology.