From: wb8foz@panix.com   
      
   > Hence the interest on what the performance implications of   
   > changing from 25 Hz to 60 Hz.   
      
   If you mean "ability to deliver power.." I can't see there is one.   
      
   a) Amtrak PRR/NEC is 25Hz/12.5KV because they lack the Congressional   
   funding to upgrade.   
      
   b) The new north-to-Boston is 60Hz.   
      
   c) From what I have read, historically, railroads used low freq   
   AC because they used series motors.  They had to, to get speed   
   control; our everyday induction motors are speed-locked to the   
   line frequency. [+/- some percentage of slip, but that's a few   
   percent..]   
      
   d) With a series motor, inductive reactance limits the current   
   they would draw. X[lr] is a direct function of frequency; the   
   lower the freq, the less it is. At DC, it is zero.   
      
   e) Modern VFD's let multiphase induction motors work over a wide   
   range of speeds. The first thing a VFD does is rectify its input   
   supply into DC, so they could care less what the cat frequency   
   is.   
      
   f) The PRR system had one advantage. By having an isolated   
   supply network [@ 25Hz] and hauling it along the RoW, with   
   frequent dedicated substations..... the train runs off the same   
   source, well 2-4 sources, & the load on the supply was almost   
   constant.   
      
   g) The new northern 60Hz leg has frequent breaks as a   
   train jumps from one power substation (and supply grid) to   
   another. The PoCo's feeding those legs must hate that abrupt   
   signle-phase 10MW load showing up then going away 4 minutes   
   later....   
      
   h) If I had a clean sheet of paper, I'd make the cat 25KV DC.   
   Change the locomotive gear to VFD's able to accept that (Not   
   sold today; but not rocket science, we have fixed switchers many   
   many times that 10MW figure.)   
      
   i) Then all the power subs *could* be in parallel, as they are now.   
      
   j) Where there is no room [tunnel] for 25 KV spacing, have an isolated   
   12KV segment; the VFD's should cope albeit with less power available.   
      
      
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   A host is a host from coast to coast.................wb8foz@nrk.com   
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