Arby Bernt wrote:
> Locomotives use AC drive systems due to the complexity of coupling the engine to the drive wheels. Before AC coupling was available, the slip between the drive wheels and the track was nearly impossible to control, as the friction of a non-slipping drive wheel can transmit more force than than a slipping wheel. By comparing the rotation of a drive wheel to a static wheel, the speed difference can be maintained at under 0.5%.
Most of the world's railway 'diesel electrics' are DC motored. AC
motors have only come in over the last 10 years and then only at the big
end. Railways have been reluctant to switch from series DC motors.
'Switchers' would still mostly be series connected DC motors, AC
traction motors are still working their way down the feeding chain.
Even then they are not all induction motors - the French were big on
Synchronous motors with slip rings for a while - I presume so they could
control the current in the rotor coils.
EMD apparently built their first AC motored locomotive in 1987, but the
first big order wasn't till '93. The same source says at 2005 , 50% of
the market was still DC motored, EMD's split was 60% AC, 40%DC.
Sounds sort of like us electric boaters - those 'new fangled AC motors'
are still not quite trusted yet :-)
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