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| Re: LIRR needs to improve ROW maintenance; new dieseld (497811) | |||
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Re: LIRR needs to improve ROW maintenance; new dieseld |
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Posted by WillD on Tue Oct 2 21:29:51 2007, in response to Re: LIRR needs to improve ROW maintenance; new dieseld, posted by Chris R16/R2730 on Tue Oct 2 20:54:24 2007. If you're going to go with AC then you have to use a fairly high voltage. The highest voltage currently used on a third rail is the 1200vdc used on the Hamburg S-bahn, although there was a French installation which was 1500vdc. I believe in both cases this is or was done with a side-contact third rail insulated from the ground by a cover extending over and under the rail. The highest overrunning third rail is the 1000vdc used by BART in California, and even then they had a bitch of a time keeping it isolated from the ground.AC has a sinusoidal waveform, as opposed to the constant waveform of DC. In order to deliver the same amount of power (assuming no induction or capacitance losses) then the average AC voltage must be equal to the DC voltage. The peak AC voltage is in turn equal to average AC voltage multiplied by the square root of two. Thus for an AC powered third rail with an average voltage of 750 volts AC the peak voltage would be 1060 volts, a fair amount above the maximum set by BART. Maybe the LIRR could incorporate what the Hamburg S-bahn has done to use 1200vdc, but why bother when wire is cheaper and more effective? |
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