• Creep control system on AC-DC GE locomotives

  • 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 Jamshid
In early 80s EMD introduced its Supper series creep control system on GP50 and SD50 models although this system was buggy and 50 series failed because of many problems which one of them was buggy creep control system :( but it brought about a robust generation of control systems with creep control ability. (I mean END EM2000 And EAS1000 control systems.)

Today along with EMD there are many companies who produce retrofit kits to upgrade old locomotives (with DC traction motors) to creep control enabled systems. ( for instance ZTR BOA and ELECON TOPS systems) and proclaim that the adhesion coefficient can be increased about 50% with their products :wink: .

Following this long introduction I have some questions about GE locomotives:

1. Do -7 , -8 or –9 locomotives have such a creep control system?

2. Is there any third party company who has manufactured these retrofit kits for GE locomotives?
  by D.Carleton
When I first started working at the Crystal River Energy Complex (Florida) in 1988 the three unit sets of SD50’s had just been replaced by four unit sets of SD40/SD40-2’s. An SD50 was left at Crystal River until enough SD40’s were retrofitted with creep-control. A few years later the SD40’s were replaced by two (later three) unit sets of DASH8-40C/CW’s with creep-control. When the occasional sets of DASH9-44CW’s showed up they were set up in the same way. I don’t recall seeing a C30-7 with creep control during my time there (1988-1999). Ironically, when the AC4400CW’s arrived their creep-control went down to a whopping 1 MPH which turned out to be too fast for the coal dumper and required a software change.
Last edited by D.Carleton on Sat Apr 10, 2004 8:01 pm, edited 1 time in total.
  by LCJ
With the introduction of the digital microprocessor-controlled systems of the Dash 8 series, GE first used what you are calling creep control. I don't recall all of the technical details, but the computer allowed a variable difference between wheel rotation speed and actual ground speed by introducing very precise control of amps to the individual motors.

This difference in speed could actually increase slightly as long as it was not increasing faster than an allowable rate. Too rapid an increase would, of course, indicate complete loss of traction.

This system increased the adhesion rate of these locomotives tremendously. A sure signal that it was working was the high-pitched singing the wheels would put out when under load at low speed -- a result of the slight slippage that was taking place (under control, as it was).
  by Jamshid
Thanks for info. :P
There is a big question over GE policies to allow other companies to built accessories to enhance old GE locomotives.

There are companies who built equipment for GE as OEM. (for example Hasler for speedometer, Woodward for engine regulator and so on ) but I have never found a company who introduced retrofit kits to enhance old GE locomotives. There are many fields to work with older locomotives, I think many –8 (or even –9) features can be tailored to –7 and pre –7 locomotives just control system must be upgraded.

With today technology it is far easier to produce microprocessor based control systems which can do any complicated procedure with software. Taking to account the magnitude of -7 fleet , and also the average life cycle of a locomotive that exceeds 30 years. There will be a virgin market to built such accessories. (Also GE by itself has not entered to such a lucrative business yet according to the best of my knowledge!)

There are many companies who have done such task for EMD locomotives but why no company entered to do business with GE locomotives.
  by jbozeman
The second version of the GE dash 7's had what was called a sentry adhesion system, like the EMD version, each TM was fitted with a speed probe and wheel rotation was monitired rather than current flow as in earlier models of GE's and EMD's. 725AF traction motors were used for the Sentry System. Like the super series EMD the GE system allowed a little creepage of the wheels which conditioned the rails for better adhesion. The Sentry system is currently a hot item, and if you know of anyone that has some surplus ones, I have buyers for them in the overseas market. It was a very good system and still very much in use.
  by Allen Hazen
I think I remember announcements o Sentry in the very late 1970s. (Had GE used that name for an earlier wheelslip control system as well? Is "Micro-Sentry" a later version incorporating a chip?)
The speed probe in the 752AF: my recollection is that this was described as essentially a small alternator built integrally with the motor. ???
You say "the second version of the GE Dash 7": just when in the 1976-1985 "Dash-7 era" was this? Am I right in thinking that the B36-7 test/demo units that went to Southern Pacific in (7770-7773, early 1980) were the first?
Was one aspect of this system having the motors in permanent parallel, with a kind of transition in the alternator? And, was the GTA-24 alternator introduced for use with this system of wheelslip control? (The relations between the GTA-11 and the GTA-24 -- what the differences were, what models got which, whether they were similar enough for a GTA-11 to be rebuilt to GTA-24 standards, whether the GTA-24 used on "Super-7" rebuilds were rebuilt from older GTA-11 -- have been puzzling me! Most railfan sources don't say anything about generator models, and I'm not confident in the ones that do.)
(Sorry to respond to your posting with a barrage of questions!)
  by Ol' Loco Guy
Sentry wheelslip control replaced CMR control in GE's catalog. Sentry is actually "digital", in that the system converts wheelspeed to a series of pulses vs. ALDAC, which converted wheel speed to a DC voltage.

"Micro-Sentry" is indeed based on the microprocessor application as used in the Dash-8's and beyond. The "brains" are in the software, so to speak.

If memory serves me, late Dash-7's and then the Dash-8's has the GTA-24 alternator applied. This alternator has two fields, which are in parallel
and each serve one group of motors. Parallel motors are a better arrangement for wheelslip control.

At some "transition"speed, the fields are connected in series.

The GTA-24 could be remanufactured from a GTA-11.
  by Jamshid
GTA11 alternator doesn't have transition while GTA24 have two windings and transition. These windings (in stator) are in parallel arrangement in low speeds and turn to series in high speeds.
GTA11 current rating just suffices 5GE761 traction motors in parallel arrangement for a six-axle locomotive.
I doubt if a GTA11 can be changed to a GTA24 one. But I curious to know if such an experience have been done so far.
  by Allen Hazen
Ol' Loco Guy--
Thanks! This is the first solid information I've gotten about a historical question that has been bugging me for a while. Many thanks!
For curiosity, how doe 761 and 752 motors compare in current draw?

  by Ol' Loco Guy

The market for aftermarket control systems for GE units is very small.
Most GE units that pre-date the combination of EFI/split cooling cannot be used in Class 1/ large regional service because they won't meet emissions stds. Modification to do so is just too expensive.

GE has their own microprocessor -based retrofit kit which is called "Bright Star." I don't know how many GE units have this equipment-but the group
of MLW MX-636's done for Hellenic Railways have both Brightstar and a retrofitted GE turbo.
  by Jamshid
Thanks Ol' Loco Guy,
It will be highly appericiated if give me a way to find more info regarding 'bright star' kits on the internet. (I can not find anything)

According to GET documents:

The max rated current for a GTA24 Alternator: 9600 Amps.
The max rated current for a GTA11 Alternator: 5200 Amps.

The max continous current for an AH 752 traction motor: 1180 Amps.
The max continous current for an AF 761 traction motor: 675 Amps.

For a Co-Co locomotive with a GTA24 Alternator, upto 1600 Amps can be fed for each motor in all parallel arangement while for a locomotive with GTA11 Alternator the max current for each motor will be not more than 865 Amps.

It is clear that for a locomotive which have GT11 Alternator (without stator windings transition), it is impossible to use six 752 motors all in parallel arrangment.

(Forgive me because of this inconvenient comparison! GTA11 alternators are look like EMD AR10 alternators, while GTA24 ones like AR11 alernators! ) :wink:
  by Allen Hazen
Thank you for the numbers. I knew that the 763 was a smaller motor (it is, for example, used on GE "export" types built for track guages as low, I think, as 915mm, where a 752 wouldn't fit inside the truck!), but i never knew just how much difference there was. Is the overall weight of the two types of traction motor roughly proportional to their capacities?
In the "NR" class locomotives of Australia's Pacific National (these are six-axle locomotives with a 7FDL-16 engine, built in the early 1990s by GE's Australian licenssee, Goninan, for Pacific National's predecessor National Rail), GE used an intermediate size traction motor, the 793: higher capacity than the 763, but lighter in weight (since the NR class was to be suitable for use over much of the national rail network, parts of which have what, by American standards, would be considered very lightly built track). I have no details about them.