NetNews Usenet Archive 1992 #31/NN_1992_31.iso/spool/rec/railroad/10139

Text File | 1992-12-22 | 3.1 KB | 57 lines

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From: [e-mail] ()
Subject: Re: Alcos, GG1's, etc.
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Date: Tue, 22 Dec 1992 20:47:53 GMT
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In <[e-mail]>, Robert Coe ([e-mail]) wrote:
>Somehow that doesn't make sense.  I'd believe "minimum" RPM, but if HEP is
>being generated by the prime mover, how could the generator possibly require
>"constant" engine RPM?  When the train is underway, the prime mover's RPM
>must depend on train speed and weight and on the terrain being traversed
>(level, climbing, etc.).  Am I missing something obvious?  Also, I thought
>that the throttle settings controlled the current drawn by the traction
>motors and only indirectly the speed of the prime mover.  Or does the whole
>discussion above apply only to the function of the throttle when the traction
>motors are disconnected?
>
>   ___            _                                           -  Bob
>   /__) _   /    / ) _   _
>(_/__) (_)_(_)  (___(_)_(/_______________________________________ [e-mail]
>Robert K. Coe ** 14 Churchill St, Sudbury, Massachusetts 01776 ** 508-443-3265

The problem isn't one of power output.  Its a problem of frequency.  On
an F40PH there is an auxiliary gearbox that spins an alternator to
provide the "hotel power".  This gearbox is set up so that when the
engine is at full speed (ie. the usual notch 8 speed), the alternator is
putting out 60 Hz power for the cars.  Therefore, the engine MUST run
this speed all the time.  At lower throttle notches the field is reduced
as noted.

There is (or at least was) a way to reconnect the traction alternator to
provide hotel power during layover.  You cannot be powering the traction
motors in this mode.  This reduces the RPM needed to generate the 60 Hz
down to around 870 rpm I think.  The main alternator is a 14 pole 3
phase AC machine as I recall.  This is still a pretty high "idle" but is
better than 1200 rpm or whatever.  It takes some doing to make the
switchover and you have to pull the plug on the cars when you do it so
they don't do it unless they will sit for quite a while.  Its hard on
the passengers when the lights go out.

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[e-mail]     208(323-3355)
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