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[quote]QUOTE: Originally posted by jruppert I was under the impression that GE AC locomotives had a separate inverter for each axle, while EMD locomotives have a single inverter for each truck. I read an article in Extra 2200 South that proposed some interesting questions of how this will affect wear patterns of wheels and that the long term effects have yet to be determined. The article was carefull not disclose any proprietary information, but proposed that wheel slip control of individual axels would promote increasing differences in wheel diameter over time, and that group control of axels should have an opposite effect of minimizing differences in diameter over time. [/quote] This is a case of someone who doesn't really understand creating a problem where a problem does not exist. From a wheel wear standpoint there is no difference between the GE and GM solutions. For the inverters to fire there must be a signal, and that signal is common to all the inverters. So if you have two inverters, six inverters, or 20,000 they are all firing at exactly the same rate. And so the synchronous speed of all six motors will be identical if you are on a GM or on a GE locomotive. The amount of creep each axle will experience will be due to the weight transfer, rail conditions, train speed and the like, and will be totally independent of whether there is a shared inverter or an independent inverter for each axle. High horsepower four axle locomotives used to enjoy an advantage at high speed. That is because any DC motor will create a "back voltage" which increases with speed. A GP only had to overcome this for four motors, while an SD had to overcome this for six motors. Thus with a small enough load, a GP could achieve a higher speed than a same horsepower SD with an identical train. The use of AC motors negates this advantage. The AC motor always tries to reach the synchronous speed being put out by the inverters. So if you need high speed today, just use an AC. The other change that has occurred is that air freight has taken away almost all of the "super hot" freight. Think FedEx. What the rails are concentrating on with the intermodal is the non overnight priority freight, where a lower speed is acceptable, but consistency is most important. That again means that the 4 axle locomotive loses its advantage.
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