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The point is that other characteristics (other than 'point of
failure') are dependant upon a "rating". Temperature rise, for instance,
is a function of the output of the machine (motor or generator). There
must be an agreed-upon load at which to determine the operating temperature (and
guarantees related thereto). Similarly, the efficiency of the machine; and
other measurable characteristics.
Incidentally, I notice a typo in my message: 5,000 hp or
3,730 kW (not 3,3730 kW).
Sorry about that.
D.
2001-10-21
The point is, no motor is designed to output exactly 5000 HP and not 1 HP
more. The motor will not fail if it was needed to drive 5001 HP.
If an engineer is clever, he just doesn't take the rational 5000 HP, convert
it with a calculator and v�ila, you have 3750 kW. If he knows that motor
can safely put out 4 MW of power, then the motor can just as easily be
referred to as a 4 MW motor. Thus, a rational number if FFU is still a
rational number in SI.
John
----- Original Message -----
Sent: Sunday, 2001-10-21 12:17
Subject: [USMA:15782] Re: IEEE per
2001-10
Whether it's 5,000 hp or 3,3730 kW, we are talking about
its rated output. Efficiencies, design margins etc. are completely
separate issues.
Duncan
In a
message dated 2001-10-20 11:11:46 Eastern Daylight Time, [EMAIL PROTECTED]
writes:
The resistance among mechanical engineers to drop the
horsepower most likely
has a lot to do with the magnitude of
numbers. A 5000 HP motor, depending
on how much over design
there is in it, can be "rated" in kilowatts anywhere
from 3 750 to 4
000 kW. In these cases, the numbers can be rescaled to 3.75
and 4 MW.
The instinct of a typical mechanical engineer is
to just convert the numbers
with a calculator and let the power in
watts come out where it does. But,
you are stuck with a "funny
numbers" that twist the tongue. Also, powers in
watts tend to
be numerically less than their equivalent in horsepowers, thus
the
motor doesn't seem to be as impressive. Mechanical engineers like
big
numbers. It somehow must make up for something else
that is lacking. As
for the power efficiency, the mechanical
engineer doesn't care. He turns
that over to the electrical
engineer to convert the hp's to watts and see
how much electrical
power is required. As long as the motor does its job,
they
don't care.
And then you get the idiotic
claims on certain household products where, for example, a shop vacuum
says "6.0 peak HP" which would equate to about 4.5 kilowatts which, in
turn, would imply its own dedicated 30 amp, 240 volt circuit! Actual
wattage on the one I have (and the one that makes this claim) is about 900
watts which would be about 1.2 HP. (The above assumes no losses in
conversion of electricity to mechanical motion, which of course isn't the
case.)
Carleton
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