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| Re: Amtrak may Lengthen Acela Express Trainsets to ''Meet Demand'' (673857) | |||
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Re: Amtrak may Lengthen Acela Express Trainsets to ''Meet Demand'' |
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Posted by WillD on Thu Aug 28 11:08:13 2008, in response to Re: Amtrak may Lengthen Acela Express Trainsets to ''Meet Demand'', posted by JournalSquare-K-Car on Thu Aug 28 09:41:28 2008. Variable frequency asynchronous AC motors of the type used in the AEM7ACs, the R142s, the PCC IIs, the SD70MACs, the TGV Atlantique, Reseau, and Duplex,and just about any other MU or locomotive built since the early 1990s do not have brushes or commutators. As i attempted to illustrate in an earlier discussion the permanent magnets are mounted on the rotor, and the field magnets are mounted on the motor housing. This means there is no need to transmit electric power to the rotor and no need for brushes. Instead because the field magnets alternately attract and repel the permanet magnets on the rotor the railcar or locomotive can sit stalled at full current without fear of burning up its motors. Even in lower torque applications, like subway cars, the lack of brushes make asynchronous AC motors VASTLY cheaper to maintain than any DC motor. The computer contolled frequency generators which inevitably accompany VVF AC motors also give then a level of efficiency and controlability unrivalled by other AC or DC motors. DC motors are nearly obsolete in all but a few applications, and those are likely sensitive to stray voltages with broadband frequencies and the mess of harmonics that could create. |
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