Western Railroad Discussion > Generators/Alternators

It is my understanding that in the first versions of the diesel electric locomotives, that the main generator was a DC machine with comutator bars and brushes. Somewhere down the line, the main generator became an alternator which is a basic AC machine followed by a rectifier package, typically a six phase bridge, to make the DC needed for the traction motors. My question is this: About when did this happen and on what model locomotives? Thanks for the help.

As far as EMD's, the GP/SD35's (2250 HP) had generators. GP/SD40's (3000) had alternators. A generator big enough to absorb 3000 HP would be too big to fit in the available space. I'm not sure about any other makes.

Alternators have been around since the 1800s. It was the advent of rugged air cooled silicon diode rectifiers which made the alternator rectifier combination practical for locomotives.

They had both. The main generator for DC for traction motors, etc and an alt for the cooling fan motors.

Nudge

The earliest I can think of an alternator being used in a traction application was the oddball GP38AC (still had a DC drive beyond that, obviously), which as I recall was the successor to the GP38 and the predecessor to the GP38-2. Iowa Interstate has a couple of them of GM&O/ICRR heritage, and I believe they retain their main alternator.
I think that NS also had a few, as probably did a few other roads I can't think of. This is off the top of my head, so if any roster/EMD experts would care to clarify that point, go for it.

Nathan
http://www.drgw.net

According to the DSG the first locomotive with an AC main generator sold by an American manufacturer was ACL 3011, an Alco C630 in 1965. The C430 also had an AC main generator.

As for EMD, the 40 series introduced in 1966 was the first. The GP/SD40 and the SD45 had the AC generator. The 38 series did not at first but starting in 1971 EMD offered the 38 series with the AR10 resulting in the GP38AC and SD38AC. The 39 series had the AR10 standard but was available with the DC generator if desired. There were only 2 straight DC GP39s and no DC SD39s.

Not 100% sure when GE went to AC but the U30B and U30C had AC main generators.

Interesting that Alco beat GE out with an AC generator even though they used GE electrical equipment.

First EMDs with Traction Alternator NYC GP40s built starting 11/65
First GEs were late model U28Bs
First Alco was C630 ACL 2011 built 7/65

EMD prototype SD40 was built with an Alternator in 1964

More than a few of these were built. LV had some, SOU 2823-2878, NW 4100-4159, not sure about B&O, C&O, or PC. I think they were only built in 1971 as the precursor to the GP38-2, which had the alternator as standard equipment.

B&O,C&O, nor PC had any GP38ACs, however L&N, SLSF (Frisco), DT&I and
CP Rail did own some.

I was in the mechanical department on the Rio Grande so I speak from what examples I had at hand plus some EMD schooling. The fact that the 2500 HP GP35 required 16 steps of transition over its speed range says it all when it comes to dealing with that much Hp with a DC traction generator. The DC generator has much tighter limits on maximum voltage and current and thus the 16 steps to stay within limits for either parameter. Not to forget that a DC main generator is a complicated machine with compenstating, commutating, shunt, and starting fields for. Then there is the high maintenance requirements of brushes and commutators and the problem of possible brush to brush flashovers (although the latter are more of a problem with DC traction motors). With an AC main generator, there is ONE field. Advances with voltages ratings of the diode banks resulted in the elimination of all field shunting in later GP40's. Field shunting induces motor instabilities that increase the occurence of motor flashovers. So a lot of advantages go along with AC machinery. It took further technical advances, but now we are witnessing the simple AC induction motor displacing DC tractions motors as well. . . Joe S.

Thank you all for your time and help. I appreciate it.