EMD Export Locomotives

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Re: EMD Export Locomotives

Postby Allen Hazen » Wed May 17, 2017 1:01 am

Aaack! In line 4 of my previous post, for "18%" read "82%".
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Re: EMD Export Locomotives

Postby Pneudyne » Wed May 17, 2017 9:00 pm

Hi Allen:

I don’t have data on hand to provide you with good answers to your questions. However, we can at least approach the topic using this set of GE main generator curves – I don’t have any comparable EMD data:

GE Main Generator Curves.gif



Which locomotive model they apply to I don’t know, but given the 1600 hp number and the engine speed schedule, I’d say it was one with an Alco engine with the GE 17MG3 or 17MG6 governor.

To start, if you look at the notch 8 curve, the central concave part, between the two non-differentiable points, represents the nominally constant-power zone where main generator excitation is under load regulator control, intended to ensure that the engine delivers 1600 hp to the generator regardless of what is happening downstream as it were. (And those GE load control systems based upon its own electro-hydraulic governor were reputed to be very precise.)

The two end points of the concave section represent maximum available generator excitation at the high-speed end (upper point) and low-speed end (lower point) respectively. Beyond each of these, the generator operates on its “natural” curve, which as my be seen, and typically of GE practice, is heavily drooped as a result of heavy decompounding. As one moves to the left of the upper point, or to the right of (and below) the lower point, the power drawn from the engine progressively decreases.

Whilst the concave section is nominally a rectangular hyperbola, in fact it deviates. The coordinates for the upper point are 1340 amps and 840 volts (as near as I can read from the graph, anyway), which calculates to 1126 kW, 1509 hp. So that is the main generator power output at that point. The lower point coordinates are 2730 amps and 390 volts, which calculates to 1065 kW, 1427 hp. So the main generator output is lower at the high-current engine of the range. If we assume that the load control system is doing its job properly and keeping the main generator input at 1600 hp, then the power lost to ohmic (I²R) losses in the main generator has increased from 91 hp at the upper point to 173 hp at the lower point, an increase of 82 hp. More current means more power dissipated in the armature winding resistance.

Now if we look at the standstill point, the coordinates are 3130 amps and 100 volts, which calculates to 313 kW, 420 hp. We could expect main generator losses at 3130 amps to be to a bit higher than at 2730 amps, say around 200 hp. So at standstill, the power draw from the engine would be around 620 hp, of which 420 hp is absorbed by the heating of the traction motor windings. In practice, of course, a standstill condition in notch 8, if there were sufficient adhesion and sufficient drawbar load to achieve it, would result in destruction of the motors if maintained for any length of time.

The lower point of the concave curve probably occurs at a road speed of 10 mile/h, give or take, depending upon locomotive design and mission. But the result is that below this speed, any efficiency calculations are fraught with difficulty because engine power utilization is also declining in that zone.

The “natural” generator curve is also load-dependent, as may be seen from the fact that the (dotted line) 4P case is different to the 2S2P case at the high-current end. One may imagine that the 2S3P case would fall somewhere between. It is not inconceivable that the continuous current capability of a 2S3P set of motors would fall well down the bottom part of the lower extension of the resultant notch 8 curve, meaning that the MCS/CTE point occurred where full engine power was not available. This would explain your apparently low-looking calculated MCS power for the low-geared SD-9 case.

I hope that helps – more to follow in due course.


Cheers,
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Re: EMD Export Locomotives

Postby Allen Hazen » Thu May 18, 2017 12:03 am

That helps a great deal! I had no idea that the efficiency loss at high-amperage (= low speed operation of the locomotive) was that extreme: I suspect it is enough to account for what at first seemed the anomalously low continuous t.e. of the Pennsylvania's Richmond Hill units (SD-7, not SD-9: PRR also had some (a larger number of) SD-9, but I think geared at 62/15).

The Stauffer book has continuous speed and continuous t.e. numbers for a large number of locomotive models, built from the late 1940s to the mid 1960s. When I get a chance, I'll go through some of them and calculate apparent efficiencies. My ***guess*** (based on a sample of two with arithmetic done in my head) is that, over time, locomotive builders got better at compensating for the physical effects you describe.
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Re: EMD Export Locomotives

Postby Pneudyne » Thu May 18, 2017 2:45 am

Here is another chart, from 1955, which compares the available power vs. installed power for several diesel-electric and diesel-hydraulic locomotives.

DE & DH Speed-Engine Output Diagrams.gif


The diesel-electrics as a group do better than the diesel-hydraulics at the very low-speed end of the range.

The article from which this was taken did not identify the locomotives involved, but some of them at least may be deduced from the power outputs and the nature of their respective curves. Here are my guesses:

A. 955 hp DE. Birmingham/Sulzer/Crompton-Parkinson Cape gauge design for Commonwealth Railways, Australia. The fairly precise power number (site gross) is the giveaway. The poorer low-speed power as compared with B is possibly attributable to its permanent 4P traction motor connection.

B. 1000 hp DE. Probably the English Electric metre gauge design for RFM Brasil. Two-stage field-shunting is apparent.

C. 2000 hp DE. BR prototype #10203. Three-stage field-shunting is apparent, as is also fairly early unloading at the top end of the speed range.

D. 1900 hp DH. Probably the Esslingen metre-gauge design for both Rio Grande do Sul and Leopoldina in Brasil. This had Voith L36r triple-converter transmission, which shows in the curve. Overall it is quite reasonable, but the unavoidable operation of the 1st converter in its low efficiency zone at starting and very low speeds.

E. 1900 hp DH. Possibly the Krupp standard-gauge design built for Algeria. This had Krupp-Lysholm transmissions, with two-speed output gears, consistent with the double-humped curve.

F. 1900 hp DH. Possibly the Krupp metre-gauge prototype built for Vale Rio Doce, Brasil, and a derivative of the Algerian design. Likewise this had Krupp-Lysholm transmissions. Neither design had an inspiring power curve.

G. 625 hp DH. Possibly the North British standard-gauge design built for Mauritius. This had the Voith L37 transmission with one torque converter and two fluid couplings. The power utilization penalty imposed by the fluid couplings is readily apparent.


Now to return from the siding to the high iron, so as to speak, here are some curves for the EMD GP9. As noted earlier in this thread, although this was a domestic model, it was exported, so may claim a legitimate place in this thread.

EMD GP9 p.03.gif


Looking at several points on the tractive effort curve:

10 000 lbf at 60 mile/h = 1600 hp

20 000 lbf at 30 mile/h = 1600 hp

28 000 lbf at 20 mile/h = 1493 hp

35 000 lbf at 15 mile/h = 1400 hp

50 000 lbf at 10 mile h = 1333 hp

60 000 lbf at 8 mile/h = 1280 hp

shows that there is a definite dropping off in power (at the rails) at lower speeds. By 10 mile/h there may have been an element of unloading as well as reduced efficiency.


Cheers,
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Re: EMD Export Locomotives

Postby Allen Hazen » Thu May 18, 2017 6:47 pm

Pneudyne--
Thank you for those graphs! Very instructive.
The 82% efficiency I remember(*) for American diesel electrics is, then, a very rough figure, likely to be right only at some intermediate speed: efficiency (= road horsepower/rated engine horsepower) will be higher than that at high speeds, lower at low speeds. The GP-9 was rated at 1750hp, and 82% of that would be 1435… which would give the right tractive effort at somewhere between 15 and 20 mph.

(And… identifying the particular diesel electric and diesel hydraulic models from an "anonymized" textbook graph is fun: sort of like recognizing the particular specimen of a species the skeletal drawing in a palaeontology book is from.)

(*) It is incorporated in another widely-known rue of thumb: tractive effort (in pounds) = (horsepower x 308)/speed (in mph). Assuming an efficiency of EXACTLY 82% would give almost this formula, but with a multiplier of 307.5.
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Re: EMD Export Locomotives

Postby Pneudyne » Mon May 22, 2017 12:30 am

Those rules-of-thumb can certainly be very simple and very convenient, but when they contain an embedded and hidden coefficient that is in fact an estimation of the typical value of a variable, then they can be misleading when used out of context. I guess it’s a case of “everything should be as simple as possible, but not simpler”; not crossing the “not simpler” line is not always so easy because it is not always very evident.

Amway, here is another EMD curve, this time for the Egyptian version of the Henschel-EMD AA16.

Egypt Henschel-EMD AA16.gif


The point to note is that at the top end of the graph, at around 15 km/h, there is a non-differentiable point above which the tractive effort curve slopes in towards the y-axis, reflecting the fact that beyond this point, full loading of the engine is no longer possible. At the higher-speed end there is no evidence of early unloading.

And this fairly comprehensive graph can be generalized in a thought context to give a qualitative picture of power distribution over the speed range. For many locomotives, unloading at the high-speed end does not happen until at or above maximum operating speed. The curve for traction power would cross the y-axis at whatever power is absorbed by the transmission at standstill at the full power position of the throttle handle.

BR Class 24 Power Distribution.gif


Sometimes some of the data is expressed in simple statements. For example, in the case of the British Rail class 37, full engine power was said available over the speed range 10 to 79 mile/h, the top speed being 90 mile/h.


Cheers,
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Re: EMD Export Locomotives

Postby Pneudyne » Tue May 23, 2017 8:44 pm

Here is a picture of what was apparently EMD’s first venture into diesel-hydraulic locomotives. I presume it was the prior model referred to by Marre in his page on the DH2 (*), and logically it was the DH1.

EMD DH1.jpg


The accompanying text was:

“Experimental U.S.A. Diesel-Hydraulic Locomotive.—The photograph reproduced below shows a 340-h.p. hydraulic switching locomotive built by the Electro-Motive Division of General Motors and powered by two G.M. 6-71 engines equipped. with Allison torque converter transmissions. This unit, designed for industrial purposes, is still in the developmental stage and is not yet ready for production.”


From the picture, it looks as if the two engine-transmission units were mounted quite low to allow direct drivelines to the outer axles of each truck. The wheel arrangement appears to have been A1-1A.

Possibly the Allison transmission units were not unlike those used on the Budd RDC, although perhaps a smaller version to suit the 6-71 engine. Or perhaps a “straight-line” version of the Allison V-drive used for urban buses.

Regarding the DH2, the picture in Marre suggests that it had the same engine location as for the SW8, judging by the stack position, and that the side panel ventilators were the same. If so, then there was not much room behind the engine for the transmission and a “dropbox” to be accommodated ahead of the rear truck. It could have been that the transmission was mounted directly to the engine, and “reversed” in layout, with coaxial shafts, so that the dropbox was right at the front, with the 3-speed gearbox behind it and the torque converter at the very rear. Allison’s V-drive was somewhat like this, with coaxial shafting that put the torque converter at the “south” end, driving back through the clutch pack (and the overdrive planetary set for the VS variants), although the reversing gears were “north” of the coaxial section. So coaxial shafting and a reversed layout were within Allison’s lexicon at the time.

Returning to the EMD DH12 export model (SNCB type 213), I have yet to locate detailed information, but it does appear to have been dimensionally identical to its type 212 (EMD AA12) diesel-electric counterpart. So the SNCB 212 and 213 may have been closer to each other than other identified line-service diesel-electric, diesel-hydraulic “twins”.

The Belgian DH12s are included in EMD’s 1986 export list, but not the EMD-powered Henschel diesel-hydraulics that were built for South Africa, and mentioned upthread. I suspect in the latter case that was because it was essentially a Henschel design that employed EMD engines. EMD probably approved this use of its engines (which at the time were not generally available to third parties for locomotive applications) but did not participate in the design as a whole, and perhaps remained mute on aspects outside of those, such as the cooling systems, that directly affected the engines. On the other hand, given that the DH12 was evidently directly derived from the Belgian version of the AA12, then as a whole it was still substantially an EMD design.


Cheers,
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Re: EMD Export Locomotives

Postby Pneudyne » Sun Jul 02, 2017 12:15 am

I have found a little more information on the Allison transmission used in the EMD DH2, attached:

DRT 195604 p.157 Allison Torque Converter.gif


In brief, it had a single-stage torque converter with two stators.

The Henschel-EMD rotary snow plough for Sweden (SJ) mentioned upthread was included in the EMD 1986 Export List, albeit without a model number:

EMD Product Reference Data Export 198601 p.48 Sweden Snow Ploughs.gif


So that I think gives it full EMD export model status, and not just associate status. The later 12-645E-engined snow ploughs listed were of the wedge type with electric drive. There is a picture of one at: http://emdexport.railfan.net/europe/sweden6.html.

Strangely though the very similar rotary snow plough built for Norway (NSB) in 1965 was not listed:

EMD Product Reference Data Export 198601 p.42 Norway.gif


As mentioned upthread, the Swedish rotary snow plough had a Krupp-Lysholm hydraulic transmission. Given that the Lysholm-Smith three-stage torque converter was a Swedish development (based upon the original Föttinger work) it is not so surprising. The SRM (Svenska Rotor Maskiner) hydraulic transmission was a Swedish-built Lysholm derivative, developed along a different vector, but in 1958, there may not have been a version of sufficient capacity for the snow plough application.

The Krupp-Lysholm transmission used a three-stage torque converter, usually followed by a two- or three-speed automatic gearbox, although no change-speed gearbox appears to have been used in the snow plough. Its main point of distinction was the incorporation of variable-incidence impeller (pump) blades in order to broaden its efficiency curve. Definitive information as to the protocol for controlling blade incidence is hard to come by, though. One source said: “The position of the vanes is regulated by the engine-speed control lever through the medium of an oil-operated servo mechanism.” Another said: “...and the position of these blades always corresponds to the predetermined injection of the engine”. Of the two, the latter seems more likely, as it is essentially input torque dependent, with rack position taken as a proxy for engine torque. A third source said: “In actual railway operation the adjustment is made automatically by the driving controller in such a manner that the fluid drive is always operated at the best possible efficiency and that the engine is protected from overload.” That is at least suggestive of a load control system, in and of itself a reasonable proposition given that, for example, in marine applications engines driving controllable pitch propellers are often fitted with load control governors that provide a set load-point (achieved by adjusting the blade angle) for each engine speed. Torque converters follow the propeller law, with torque absorption capacity increasing as the cube of the rotational speed.

The EMD 8-567C engine fitted to the Swedish Henschel-EMD snow plough came with its customary Woodward PG governor with electro-hydraulic speed control. If it also retained the customary load control system, then perhaps that was used to control torque converter impeller blade angle so as to provide a set load point for each engine speed. Most, if not all other railroad hydraulic transmissions did not require load control. So, the Krupp-Lysholm type was unusual in that respect.

Overall, the EMD 567 engine was rarely associated with hydraulic transmission, but the few installations that were made certainly covered a range of transmission types. These included the Allison, Voith triple converter, Krupp-Lysholm, and Voith two-converters-plus-one-fluid coupling varieties.

Cheers,
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