• Alternators... asking again

  • 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: MEC407, AMTK84

  by Allen Hazen
I would like to get straight on the alternator models used on GE locomotives in the Dash-7 period. Greg McDonnell's "Field Guide to modern Diesel Locomotives' (Kalmbach) says that the GTA-11 was used on:
---C30-7 (including Conrail's C30-7A) and that the GTA-24 was used on:
and also that the GTA-24 was used on all "Super-7" rebuilds. I am not altogether confident of McDonnell's accuracy, however.
My suspicion is that the GTA-24 was introduced in conjunction with the new,"Sentry," wheelslip control, in which case at least early B30-7 would NOT have had it (but would have had the GTA-11).
Any information?

  by jbozeman
The GTA11 started out on the old U boat series of GE's, including the U23B, U23C, U30's and even the U36B. It was adapted to the Dash 7 model in 1977 (that is where dash 7 comes from) and was used into the mid 80's as their preferred alternator. The earlier GTA11 did not have the tripod mounted diode banks, they were actually mounted on the firewall between the alterntor and the equipment blower. All of the B's and C's used the GTA11 until the introduction of the GTA24 around 1984 or 85.

All Super 7's got the GTA24 which is a superb machine. It is a transition alternator, in that it has two SGC contactors mounted on top that change the output of the alternator by changing the internal connections from series to parallel. Super 7's do not transition their traction motor connections as to those with GTA11's. All GTA24 applications also came with the Sentry Wheelslip adhesion system.

Your assuptions are correct, in that all late 70 and early 80 GE's 2300 HP and above got the GTA11, including the B30-7. I am most familiar with the B36-7 models purchased by CSX in the 80's which had GTA24's and Sentry. NS also purchased some C36-7's that had GTA24's and Sentry along with Dash 8 style load/dynamic brake resistors mounted behind the engineer's cab. I currently have one of these in my shop.

Let me know if I can be of more help to you. :wink:

  by DutchRailnut
how do you change Alternator from Series to parallel ??

  by 498
By changing the electrical connections between groups of windings.

  by DutchRailnut
I understand in Generators but in Alternators ???
  by LCJ
Technically, I believe an alternator IS a type of generator (of current) that is designed to produce alternating current. On locomotive applications, alternators have their output current rectified to DC for use by traction motors. Changing connections between stator windings within the alternator (transition) changes the speed the locomotive can achieve within geared limits.

Units with AC motors have computer-controlled invertors that then produce AC at specific frequencies.

DC generators, with armatures and brushes to conduct output current generated on the armature windings by the static field windings, has to have transistion circuitry outside the generator, usually in the high voltage control cabinets.

  by DutchRailnut
Series/paralell were taling about stator/rotor on a Alternator the rotating field is low current, the stator is high current so it can't be in series.
As far as Alternators Ive heard of reconfiguring stator from star/delta configuration but never series/parallel. and Ive been in maintaining/operating locomotives for 20 plus years. so yes I would like to see a schematic of this event.
  by Allen Hazen
Thanks, jerry Bozeman! Between you and Ol' Loco Guy (in his post to the "Creep control" string on this forum), I'm getting answers to questions that had been bugging me for a long time! (Are you sure the GTA-24 wasn't introduced until 1984/1985, or was this just when CSX got its first units so equipped? The first production B36-7 were built in 1980, and I think I remember reading that MP's production B30-7A of 1981, though not the experimentally uprated B23-7 of the previous year, had the new wheelsip contol system which I have assumed used the GTA-24.)
As for transition... Series/parallel connections of the traction motors get you different voltages: when the t.m.s are in series, the voltage supplied by the generator is divided by the number of traction motors to get the effective voltage delivered to each t.m. The "alternator transition" used with the GTA-24 is supposed to et the same effect: I assume the idea is to increase the voltage from the generator at higher speeds so that the traction motors "think" they have been re-wired in parallel even though they are still physically connected in series. I guess -- as you can all tell, I'm NOT an engineer -- that this is done by reconnecting circuits in the stator of the alternator: that different parts of the stator windings which, at low speeds, are operating in parallel to one another, get put into series at higher speeds.
"Star" means ... there are six places where power comes off the stator (and is used at lower speeds) and "Delta" means there are only three, each giving twice the voltage??? Or have I tried to guess too far outside my own experience?

  by DutchRailnut
In delta the 3 coil's are connected at phase only with each other.
In star the one side of coils is connected to neutral and other ends are your phases. usualy used to start large AC machine's but very usable to reconfigure AC generators to provide a 58% voltage reduction.
  by Allen Hazen
Dutch Railnut--
Thanks for star/delta information.
Jerry Bozeman--
Re your mention that early GTA-11 didn't have the "tripod" mounting of rectifiers, but had rectifiers on the firewall: I may have an illustration of that. On George Elwood's marvelous "Fallen Flags" rail photo site there are a number of diesel locomotive operator's manuals, including one
listed in the index as being for an Alco C-430, but covering the C-630 as well. The general arrangement / location of equipment drawings show the rectifiers as hanging on the front wall of the compartment containing the alternator, etc. (The identifying number 41 is clearer on the C-630 diagram than it is on the C-430 one.)
I'm not sure the alternator is a GTA-11, though. The shape looks a bit off (which could just be bad draughtsmanship), and I believe that the earliest alternator-equipped U-series, and alternator-equipped Alco C-series, had a (more expensive and over-engineered?) model, the GTA-9.

  by Ol' Loco Guy
I believe that the C430,630 and 636 had the GTA-9-which was GE's first attempt at a traction alternator. Does anyone care to guess why GE let
a competitor/customer roll out a brand-technology in THEIR product (C630) rather than in a GE locomotive design ?

Anyhow-it is not hard to imagine that the GTA-9 may have been over-engineered given that it was a first attempt at a new technology. So, I suppose that one could also assume that the GTA-11 could be considered a "simplified" version of the GTA-9.
  by Allen Hazen
Tom Gerbrauch (sp?), a retired GETS person who contributed to this forum (the ancestor of this forum?) two or three years back, had a story about the two alternators.
Apparently someone in the GE hierarchy had suggested that if TS wanted an alternator they should get it from power systems (another division of GE). The head of GETS saw this as an attempted powergrab, and insisted that GETS would design its own traction alternator, thank you! And then -- since failures of the GETS design after this episode would have been VERY embarrassing -- told his design staff to make sure their alternator could take the worst the railroads could dish out. Result was very big: so big that it needed much less cooling air than a GTA-11 in normal service. GTA-11 was a later, cheaper, design, with significantly lower amperage (and a bigger ventilation fan). ... I believe that some of the old posts are archived somewhere; I don't know if Mr. Gerbrauch's is findable.
As for why GE let Alco introduce AC/DC transmission... Well, Alco was (by this time) desperate, and doubtless asked GE for something that would let them get the jump on the competition. GE was, I think, very proud of their big DC generator on the U25B and thought it would be good for somewhat higher ratings. The four-unit U28/30/33/36B test/demonstrator locomotive set (built early 1966) was originally intended to comprise two with AC/DC and two with straight DC transmission: to its dismay, GETS found that the railroads all wanted AC/DC (Tom Gerbrauch said there was a several months' draught of new locomtive orders at GE after the unmentionable (grin!) competitor released the GP40). And so they changed plans to concentrate on AC/DC r&d, building a second pair of AC/DC test units (the two DC units being sold to the New York Central). (Builder's numbers for the GE test and the NYC U28B had made me suspect something like this; details of story pieced together from many posts by several people to the GE and New York Central forums.)
  by Allen Hazen
SOME old Railroad.net forum strings can be accessed through

So far, though, I haven't found the old posts mentioned above by Tom Gerbrauch and others.
  by Allen Hazen
I've found something relevant to the question of how long it took GE to switch from the GTA-9 to the (cheaper) GTA-11. George Elwood's "Fallen Flags" rail picture site has drawings and data extracts from a 1973 Erie-Lackawanna locomotive diagram book, at
E-L had two orders of U33C. The first order, built in 1968, had the GTA-9 alternator; the second, built the next year, had GTA-11: in particular, GTA-11A1.
The question on all of your lips is, of course, "Did they revert to the higher-rated generator for higher horsepower locomotives?" And the answer is, NO: the GTA-11 was good for a 3600 hp unit. E-L's U36C, built in 1972, came equipped with GTA-11C1 alternators.
And, for dedicated pursuers of trivia, the passenger (HEP) equipped U34CH had... GTA-16A1 main alternators. HEP was generated by a separate generator (if you are wondering where it was located-- note that a U34CH doesn't have the usual central air intake on the side of the long hood behind the cab (Grin)), but apparently providing the mechanical connection for it (hmm-- or maybe the constant-engine-speed operation required for HEP in those days) necessitated a new main alternator design.
I believe that one U34CH as been preserved at a New Jersey museum. If some railroader with acquaintance with old GEs could get permission to look inside, and describe what's in there....

  by EDM5970
I've pulled some parts off U-34CHs in a scrappers yard, and will back Allen's statment about the HEP alternator location. It was between the main alternator and the cab, connected to the main alternator by a driveshaft. If I remember correctly, the central air intake was at the radiator end at these units; next time I'm at that yard I'll take a better look.

I do remember a lot of variation between different GE models, and even within the same model. Contactors that were in one place on one unit were not in the same place on the next one. These were all early units, built before GE got their act together.