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Re: [BRHSlist] Digest Number 1868

To: BRHSlist@yahoogroups.com
Subject: Re: [BRHSlist] Digest Number 1868
From: William Barber <clipperw@EarthLink.net>
Date: Fri, 7 Nov 2003 11:35:58 -0600
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Wolfee,

An F40PH provides both propulsion power and head end power (HEP) for 
train lighting, heating and air conditioning. The train power is 440 
volt AC and to provide it at the proper frequency for the various 
motors and other equipment in the cars, a constant diesel engine rpm 
must be maintained. If it is not, the frequency will fluctuate causing 
damage to this equipment. Maintaining a constant engine rpm is totally 
independent of main generator traction load. Thus, when the engineer 
moves the throttle, only the main generator (or technically alternator) 
excitation is being changed. The excitation of the main generator 
determines the amount of traction power output and thus, the movement 
of the locomotive. Therefore, when the HEP is operating, the engine is 
at full rpm even though the locomotive may be at a standstill. Amtrak 
GE P42s do the same thing.

When the HEP is off line, normal engine speed variation occurs with 
throttle position change. The sound made by HEP equipped locomotives, 
particularly in closed stations such as Union Station in Chicago, has 
been one of the primary objections to such locomotives. The new METRA 
Boise locomotives have separate HEP systems driven by smaller quieter 
diesels (Caterpiller, I believe). Engine crews also don't like the 
constant high engine rpm sound in the cab. Frequently, on multiple unit 
consists such as Amtrak trains have, the crew will set up a trailing 
unit to provide train HEP power, thus quieting the cab. None of the HEP 
systems that I know of can be m.u.ed with each other like traction 
power of the locomotive can be. Thus train length is somewhat limited 
by the HEP available from one unit.

Bill Barber

On Friday, November 7, 2003, at 09:29 AM, BRHSlist@yahoogroups.com 
wrote:

>    Date: Fri, 07 Nov 2003 15:22:49 -0000
>    From: "wollffee" <wolfee@onebox.com>
> Subject: How does an F40PH work?
>
> I found the operators manual for this loco and it states that the
> engine runs at 893 RPM at ALL times during normal ops.  Yet, it still
> has the normal 8 power setting positions.  If the motor always runs
> at full speed, how is power to the wheels adjusted?


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