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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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