From: rcp27g@gmail.com   
      
   Clark F Morris  wrote:   
   > On Sun, 14 Feb 2016 11:28:14 -0000 (UTC), bob    
   > wrote:   
   >   
   >> Clark F Morris  wrote:   
   >>> On Thu, 11 Feb 2016 07:21:49 -0800 (PST), rcp27g@gmail.com wrote:   
   >>>   
   >>>> On Thursday, 11 February 2016 03:24:33 UTC+1, Stephen Sprunk  wrote:   
   >>>>> On 09-Feb-16 10:49, 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.   
   >>>>>   
   >>>>> 12.5kV means four times as much current as 2x25kV, but if they think   
   >>>>> their decrepit infrastructure can handle the load, c'est la vie.   
   >>>>   
   >>>> As I pointed out elsewhere in the thread, DB (German railways) operate   
   >>>> significantly higher power trains (200 mph ICE3 units) under 15 kV 16.7   
   Hz catenery.   
   >>>>   
   >>>>> Variable-tension and 25Hz are far more pressing problems that can be   
   >>>>> corrected independently, though it'd be wise to do both in a way that   
   >>>>> makes moving to 2x25kV later much easier.   
   >>>>   
   >>>> The constant tension catenery is the biggest impediment to improved   
   >>>> performance on the NEC.   
   >>>   
   >>> My point was about 12.5 KV at 25 Hz vs. 12.5 Kv at 60 Hz.  If I   
   >>> understand Stephen correctly, with modern equipment the difference in   
   >>> power factor  becomes neglible unlike say 25 - 30 years ago when I   
   >>> first heard about this.   Thus it was about how much power could be   
   >>> transmitted to the train at a given voltage and frequency.   
   >>   
   >> Right, but there are plenty of examples of high power locomotives on the   
   >> Swiss/German/Austrian 15 kV 16.7 Hz networks that cope with low frequency   
   >> and not much higher voltage. Going back to the days before power   
   >> electronics, for example the Swiss Ae 6/6 were built starting in 1955 and   
   >> are rated at 4.3 MW which is within the range of modern high speed train   
   >> power cars. Modern European locomotives are all designed to run on the main   
   >> four systems of 25 kV 50 Hz, 15 kV 16.7 Hz, 3 kV DC and 1500 V DC. While   
   >> they sometimes have a lower power output on DC, there is no problem with   
   >> the low frequency system.   
   >   
   > As I understand it, the amount of AC power that can be transmitted at   
   > a given voltage is inversely proportional to the voltage.  Thus a   
   > train that could get the required power at 15 KV 16.7 Hz could not get   
   > it at 15 KV 50 Hz.   
      
   I don't follow. 15 kV is the same voltage at 50 Hz as it is at 16.7 Hz or   
   any other frequency.   
      
   > Also I note that at least some of the   
   > multi-voltage ICE trains and TGVs have different power ratings   
   > depending on the power source.   
      
   Right, but that's because the current, and hence electrical losses are much   
   less at 25 kV than at 15 kV. The fact that one is 50 Hz and the other is   
   16.7 Hz is not the issue.   
      
   There are separate frequency dependent transformer related issues, but   
   these are not related to the voltage.   
      
   Robin   
      
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