From: stephen@sprunk.org   
      
   On 10-Feb-16 09:20, Clark F Morris wrote:   
   > Jishnu Mukerji  wrote:   
   >> Amtrak is neither changing the voltage nor the frequency on NEC   
   >> south. They are adding 25Hz capacity. They don't foresee any   
   >> problem with operating at 160mph using 12.5kV 25Hz.   
   >   
   > From what I gathered from Harry Rappaport's (I hope I remembered the   
   > name correctly), the problem would come if they went to 60 cycles   
   > and stayed at 12.5 KV.   
      
   As noted in previous replies to this claim, power factor goes down as   
   frequency goes up.  Trains of Rappaport's era started with a mediocre   
   power factor at 25Hz and got much worse at 60Hz, but modern trains run   
   at nearly unity with _any_ frequency input, so it's now moot.   
      
   I can't find an actual formula, but the examples I've seen look like   
   doubling the frequency squares the power factor: 0.8pf at 25Hz means   
   ~0.6pf at 60Hz, but 0.99pf at 25Hz means ~0.98pf at 60Hz.   
      
   > From postings here the problem with 25 cycles is the weight of the   
   > transformers and possibly other electrical equipment.   
      
   The onboard problem is the higher transformer weight (and cost); in   
   modern trains, the power goes directly from the transformer to the   
   rectifier, and everything else onboard runs on DC power--at unity.   
      
   The wayside problem is the enormous cost of maintaining your own 25Hz   
   power distribution network vs just using the 60Hz grid, which has far   
   better economy of scale than you could ever dream of achieving.   
      
   S   
      
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