In essence, yes. Whether it is running at a constant speed
or is being controlled by the throttle all diesel-electric
engines operate pretty much the same way.
The governor supplies fuel to the diesel to the extent
necessary to maintain the target rpm. As the load, which is
controlled by field excitation, increases or decreases, the
governor adjusts the fuel supply.
For example the F3, (only manual within easy reach), idles at
275 rpm. As the throttle is advanced each notch the diesel
tries to increase it's speed in 75 rpm increments until 800 rpm
is reached in the 8th notch.
Meanwhile the load regulator is exciting the generator field
current to produce the horsepower that corresponds to a given
throttle position. For example if the unit is left in the 7th
notch the diesel will turn no faster than 725 rpm and the load
regulator will not tell the main generator to output any more
than a theoretical 1312.5 hp, (7/8 of 1500). The reason I say
"theoretical" is that the diesel has other loads on it which
are not translated to horsepower at the rail. If you are at
this steady speed in the 7th notch and the air compressor or
cooling fans kick in or out the unit has to make small
adjustments in fuel and excitation to keep the power output
stable.
It's quite obvious that an idle speed of 893 is going to consume
more fuel that an idle speed of 275 rpm but we've already
addressed that issue.
Anything else?
Russ
----- Original Message -----
From: wollffee
To: BRHSlist@yahoogroups.com
Sent: Friday, 07 November, 2003 10:07
Subject: [BRHSlist] Re: How does an F40PH work?
Thanks, I understand. In addition to adjusting the
generator/alternator, can they also adjust the output of the diesel?
In other words, can 893 rpm produce, say, 1000hp when it is given
less fuel under minimum load and produce 3000 under maximum load with
a lot of fuel?
--- In BRHSlist@yahoogroups.com, "Russell Strodtz" <vlbg@e...> wrote:
> Engine RPM can not be directly correlated to HP output.
>
> As has been mentioned before in this forum neither the
> traction motors or the main alternator have built in fields
> with permanent magnets.
>
> Power output of a constant speed diesel-electric can be
> controlled by adjusting the current level applied to the
> field excitation of the main alternator.
>
> Constant speed diesel-electrics have been experimented with
> for freight locomotives but the fuel penalty is just a little
> too high.
>
> Constant speed diesel-electrics are, pretty much, only used
> in passenger operations. The lighting, heating, and air
> conditioning needs of just about all modern passenger equipment
> are supplied by trainlined electrical cables connecting to the
> locomotives. In the case of some locomotives there is a separate
> diesel-electric power supply that handles this task. On some
> others the equipment's power needs are supplied by another
> alternator connected to the diesel used for propulsion.
>
> Since the equipment's needs stay the same whether the train is
> moving or not the constant speed diesel is necessary.
>
> Think about standard rapid transit equipment. Every time there
> is a gap in the third rail at a switch or something the lights
> briefly go out. This is not a problem since the gaps are short
> and the train is still moving and very shortly picks the power
> back up again.
>
> A loss of services at station stops or a reduction in available
> power going downhill or drifting would not be acceptable in
> passenger service.
>
> Russ
> ----- Original Message -----
> From: wollffee
> To: BRHSlist@yahoogroups.com
> Sent: Friday, 07 November, 2003 09:22
> Subject: [BRHSlist] 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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