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| Re: Why isn't Alternating Currentu used to power Subways? (was R1/9 acceleration) (664948) | |||
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Re: Why isn't Alternating Currentu used to power Subways? (was R1/9 acceleration) |
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Posted by Jeff H. on Mon Aug 11 03:20:37 2008, in response to Why isn't Alternating Currentu used to power Subways? (was R1/9 acceleration), posted by JournalSquare-K-Car on Sun Aug 10 12:06:09 2008. We've only been through this a hundred times before on this board.There is no engineering advantage to using low-voltage (600-1000) volts AC on the third rail. The slight efficiency gain from using multi-tap transformers instead of resistors to accelerate the train (remember, the resistors are only in the circuit for a short period of time....the bulk of the energy consumed by the motors happens in full series or full parallel) would be more than lost by the lower inherent efficiency of single-phase AC commutator motors (that's what the GG1 used). Also, because of skin effect, the transmission losses on the low-voltage side would be higher. The reason single-phase AC was used at all was that it was coupled with high-voltage catenary distribution. All this is quite moot, since all modern transit equipment is using 3-phase induction motors with solid-state inverter drive, which is much more efficient. |
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