In the late 50's-early 60's, 4-motor:applications with 500-600 hp/axle were seen as sailing in uncharted waters. Case in point: Alcos' DL-640 proved to be slippery in service...and NYC DL-721's were show to exhibit synchronous slip.
The solution was to upgrade the original design of the ALDAC wheel slip controls , which measured individual axle speeds, to account for these conditions. This equipment was applied to the Century series.
The U25B (designed for full parallel operation-but ultimately constructed with transition) featured an additional wrinkle,using the same ALDAC equipment.. This would be a slip suppression brake valve, which made a momentary independent brake application in order to condition the wheel treads.
EMD did not have a competitive wheel slip control until IDAC, which was introduced on the 40-series.
Same speed at the same tractive effort. Same speed with reduced tractive effort, use higher gearing. In either case, reduced speed or reduced tractive effort, either means reduced power. Note that the real reason is not the voltage limiation of the generator but the current limitation of the motors. Four dc motors cannot do the job of six. With AC, there are some vaiables that come into play, but overall the principle remains, just that most AC locos have more motor capacity than needed to use the power.
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
On a related note, having 6 motors instead of 4 allows for more steps in transition, i.e. 6 motors in series, two sets of 3 motors in series, three sets of 2 motors in series and all 6 motors in parallel. The traction generator used on the SD24 was probably limited in voltage/current range when fed with 2400 HP.
Thanks! That makes sense. Even if it was a GP24, they would have had trouble getting all the power to the railhead, from what I have read about the GP30's "slipperiness".
Thanks again,
NW
The 567D3 and main generator were capable of producing 2400 hp - EMD engineering was concerned about applying 2400 hp to only 4 traction motors. This same concern was also present in the GP30 with the D47A or D57 traction motors. The GP35 had D67 traction motors and the 567D3A power plant allowed 2500 hp. EMD has always been 'conservative' through the years...
Jim
Modeling BNSF and Milwaukee Road in SW Wisconsin
Hello all.
I've had a question that has bugged me for a couple of months now, but I can't find a good answer.
The SD24, EMD's first production turbocharged locomotive, were rated at 2400 HP. The GP20 came out a couple months later at 2000 HP. The GP30, introduced two years later, was rated at 2250 HP, after the 2500 HP U25B came out. So, why was the GP20 not a 2400 HP GP24?
Was it because of wheelslip?
Technical reasons to use the 567D2 over the 567D3?
Thank you,
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