• U25B thoughts

  • Discussion of General Electric locomotive technology. Current official information can be found here: www.getransportation.com.
Discussion of General Electric locomotive technology. Current official information can be found here: www.getransportation.com.

Moderators: AMTK84, MEC407

  by Herr Spreng
The GE locomotive design group was separate from and shared no personnel with the Alco design group. The chap who ran the U25 group was said to be somewhat enamored with the EMD way of doing things on the electrical end.

The goal on the electrical side of the U25 was to make it 'simple' like an EMD. Some of the devices even had EMD names,e.g., the start contactors CK1 and CK2. All of the 'junk' that caused problems on the Alco road units was eschewed and replace by 'off-the-shelf' assemblies. Case in point: The Woodward PG-R governor replaced the GE governor and control panel.

Another goal-never realized-was a permanent parallel traction motor coonection arrangement-hence the application of the large GT-598 DC machine with a GY-50 three-field exciter.

The strange irony was that the EMD equivalent, the GP-35, had a complicated (and troublesome)transition scheme that mirrored some of the shortcomings of the Alco-GE road passenger units with the multi-point field shunters.

  by Allen Hazen
Your post SHOULD have been the start of an interesting string! I'm not sure I have anything useful to add at this point, which is why I haven't replied until now.

--Certainly simplicity was a major goal in designing the U25B. I recall a GE press release from the 1960s boasting that it had only (a very small nyumber-- 7, I think) or rotating electrical machines above the frame. (Below the frame there would be at least another eight-- four traction motors and four axle-end-generator-speedometers for the wheelslip control.)

--Another participant in this forum (one who used the name "Old Loco Guy") mentioned several years ago that the U25B was originally intended to be a permanent parallel machine, but I have never seen any other references to this. Can you fill in some details?

--Of course, the GT-598's size and robusticity, whatever the role of hopes of eliminating transition had in motivating its use, ALSO gave it some "growth" room: it was used on the 2800hp U28B, and I have read somewhere that GE's engineers initially hoped it would be good for 3000: which may be why GE was several months behind EMD and Alco in introducing AC/DC locomotives.

  by EDM5970
Ummmm, lets see, 7 rotating devices above the frame- Main, aux. and exciter generators, fuel pump, DB blower, and two cab heater blowers. No need for a crankcase exhauster, as GE pioneered the eductor. The three field/Woodward combination doesn't need a tach gen.

Just an educated guess, comparing Alcos (that I know a little about) with GEs. Was my guess close?

In regard to the three field, Alcodoc (over on the Alco forum) made a comment that the greater torque that a U-25's 16 cylinder engine produced, as compared to the 8-251 in a C-415, allowed the three field to be a success.

EMDs were not known for torque, or at least that is what I was told many years ago by a CMO. That is why the have to rev a bit before loading up; they also have to get oil to the load regulator. This lack of torque probably explains, in part, the multi-step field shunting.

The other part of the multi-step puzzle, of course, was the main generator. The EMD generators in the GP-30 and GP-35, as well as the 581 (specifically in the C-424) were at about the maximum size and current limits for use in a locomotive. The use of the 598 on the C-425, at ELs request, allowed the retirement of the multi-step field shunting for Alco.

Going to alternators solved most of the field shunting issues for everyone. Eventually, EMD got the GP-40 to be a permanant full parallel machine, although I think it still had some field shunting.

Interesting threads (several), comparing the different builders and their solutions to similar problems.

  by Herr Spreng
Subtract the d/b blower (grids located and cooled by the 'helicopter' in the radiator cab and the two cab heater blowers ( a good sized heater core blown by a bleed off the main equipment blower) on a U25.

GE used three-field on all manner of export locos with the C-B engines before it was applied to the U25B. Also used on at least some of the smaller 6 cylinder Aussie Alcos.

On a GE generator, the generator characteristic curve differs only slightly based upon the type of exciter or control-be it internal or external. The contorls and exciter define the curve-not the main generator.

  by Allen Hazen
I don't know the list: I read only the bost that there were only seven (if it WAS seven), and that was a LONG time ago: it may have been quoted in a "Trains" article of the 1960s (and may not). I think it was specifically about the number pof rotating ELECTRICAL machines-- is the fuel pump run by a separate electric motor?

Dynamic brake blower is an interesting test case of the GE design philosophy. I always thought the U25 (+ later U-series, + most Dash 7) use of the radiator fan to blow cooling air past the DB grids was a more "elegant" solution than the competition's use of separate, motor-driven, fans: when you are in DB mode, the engine isn't working at full power, so why NOT use the same stream of cooling air for DB grids as for radiator, and if you are using the same stream of air, using the same fan seems like an obvious idea. The Dash-8 and later locomotives (actually started just before that, with the B30-7A1) went the other way, and used separate DB blowers. I take it that the theory was, by this time, that the efficiency improvements of using just enough air for each application (and turning off the blower when you were using the other) were enough to justify the added complexity and components.

What's the best design philosophy? speaking as a professional philosopher, I guess the lesson is that you can't say "best" about locomotive design in isolation: what the best locomotive design is depends on the operational and economic environment the locomotive will be used in.

  by LCJ
Fuels pumps were driven by DC electric motor.

EMD DB fans were driven by DB current, and as such were not a load on the engine/generators.

As for U-series (especially U25) we used to say (in reference to the large, always spinning cooling fans) you could turn one of those units upside down and it would float on a cushion of air.

One problem with using the same air stream to cool both the DB grids and the radiator flow was that prolonged use of DB could cause the engine to overheat on occasion. Of course, dynamic brake systems weren't what they are now, in terms of effectiveness and utility, anyway. U-series DB grids melting down gave off quite a show after dark!

As I believe I've commented before in this forum, the U25 cab heater blower had a tendancy to suck exhaust gases into the cab when the air control was opened in the operator cab. This factor was named in at least one major train accident that I know of (head-on collision, Penn Central at Mt Marion NY, in December 1970, I believe).

Running big fans (or blowers, or compressors) continuously just doesn't fit with $2+ (US) fuel oil these days. Minimizing energy waste at every opportunity is current requirement. On-demand running of highly efficient 3-phase AC motors fills the bill.

But I understand that things were much different in the early 1960s.

I always thought EMD's solutions were, although admittedly more complex, a more intelligent overall design -- controlling air flow over radiators rather than controlling water flow through radiators.

  by EDM5970
Alco used a right angle drive and eddy current clutch to run radiator fans on the 244 and 251 road units. Interestingly enough, this unit was made by GE. There were a couple of control schemes, and I'll describe how the simplest one worked.

At lower engine temps, the fan was not turning, and the shutters were closed. As the engine got warmer, the fan would run at roughly half engine speed; a resistor in the coil circuit allowed the clutch to slip. The second stage bypassed the resistor, and the fan ran at full speed. The shutters opened at the slower speed, IIRC.

(There was a more complex system that used modulating shutters and several stages of resistance in the coil circuit, but I've never seen one, fortunately; only in some of the service manuals. It seemed too complex, a real maintainence headache, which probably explains why none of the 251s I'm aware of used it-)

I always thought that GE had kept the eddy current clutch for the U-boats. I do know about the fluid amplifiers and using various numbers of radiator sections, which to me is another complex solution.

I've seen ads for inverter type fuel pumps with AC motors. They get a DC input, but the motor is three phase AC, with its own onboard electronics. No brushes to maintain, which goes along with GEs use of three phase motors just about everywhere on the AC4400s and up.

As an Alco guy, I do have to admit that EMD had it right with the three phase radiator and TM blower motors. It only took GE how long to adopt that philosophy to compressors, radiator fans and TM blowers? (And also kudos to Winton for the unit injector-)

I was thinking Alco in my previous post when I mentioned DB blowers and cab heaters. And at one point I was even exploring the possability of restoring a certain C-420's DB capability with GE grids in the radiator compartment. I forgot-