[GreenKeys] History - Why voltages and frequencies are chosen (5v & 3.3v logic, 6.3v filaments, 120/220 VAC, 50/60Hz etc)

[Paul Wills]

Good point regarding the filament voltages.

The 25 cps areas are all at 12KV.  Some time in the past, they raised all 
the voltages:  135KV to 138 KV transmission, 6600V to 6900V signal power, 
and 11KV to 12 KV for the catenary.

PDW
  ----- Original Message ----- 
  From: Charles Ring
  To: Paul Wills
  Cc: Greenkeys at mailman.qth.net
  Sent: Wednesday, November 21, 2012 6:59 PM
  Subject: Re: [GreenKeys] History - Why voltages and frequencies are chosen 
(5v & 3.3v logic, 6.3v filaments, 120/220 VAC, 50/60Hz etc)




  On 11/21/2012 1737, Paul Wills wrote:

    Actually it's 16 2/3 Hz.  It's exactly 1/3 of 50 Hz.  It allows a simple 
1 to 3 ratio of poles on each end of the MG set.


  I think the only mystery remaining here is, why 6.3 volts for tube 
filaments, and i will add why also 5 volts for rectifier filements?


    Amtrak still runs 25Hz from the east end of Sunnyside Yard (New York 
City) and Washington, DC as well as the Harrisburg line.  SEPTA (The 
Philadelphia commuter authority) also runs 25 Hz but mostly because they are 
the "tail" being wagged by the Amtrak "dog."

    They're committed to it for the long term as most of the rotary 
frequency changers have already been replaced with solid state units. 
(There are also two, I believe, hydro-electric generators on the Susquehanna 
river at Safe Harbor dam.)

    PDW


  Are the 25 cps areas also still 11,000 volts?



  -- 
  Charles Ring W3NU


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