'A 5000 HP motor can be rated anywhere from 3 750 to 4 000 kW or 4 MW in short'.
If they (mechanical engineers) feel that 4000 KW is smaller than 5000 HP, then they can use plain 4,000,000 million watts and that will look very big. Even auto enthusiasts boast their vehicles as 240 hp, 350 hp, etc and their electric equivalent seems small for them. But the hybrid electric cars are going to change all these things and Honda is coming with hybrid civic in early 2002. Madan __________________________________________________ Do You Yahoo!? Make a great connection at Yahoo! Personals. http://personals.yahoo.com
2001-10-22 For those who can't open a word perfect document, below is the context of the text. 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. Mechanical engineers don't seem to grasp the importance of significant figures when converting numbers. Anything in fractional inches usually no finer than 16-ths, can be converted to whole millimetres with any decimal remainder rounded up or down. When I added millimetres to old mechanical drawings, or updated old inch drawings, I never converted a fraction to an odd millimetre. Example 9/16 = 0.5625 in = 14.2875 mm. I would do the conversion as 9/16 = 0.56 in = 14 mm. And I never had a problem doing this. When I criticized a mechanical engineer once about not using significant figures when converting fractions to decimals, he got very mad. His content was that 9/16 IS 0.5625 and not 0.56. I told him a machine shop would charge more to make a piece to 0.5625 then to 0.56, because the extra time and precision required. And if it isn't needed, it shouldn't be requested. But, I was talking to the wall. Looking through electrical magazines and catalogs, the use of SI is more prevalent. But looking through mechanical magazines and catalogs, you would think SI doesn't exist. But, it is funny to increasingly see "hidden metric" in the numbers. It must make these luddite mechanical engineers boil over to see numbers like 1.97 in (to us 50.0 mm) instead of 2.0 in. Mechanical engineers will be the last hold-out. John This is about units of measurement. See "Sparks", Pg. 44 of IEEE POWER ENGINEERING REVIEW 2001 October. In "World's First HTS 5,000-HP Motor", we see horsepower featured to quantify output power. The input to that motor would, almost certainly, have been measured in watts. That being the case, how would the efficiency (output/input) have been expressed? - hp/kw? And supposing the electrical losses would have been measured in watts (kW, MW etc.), would the mechanical losses be in hp?. This, by any standards, would seem to be an irrational situation. The IEEE has made great strides in adopting the World system of units, SI. How can we, engineers, extricate ourselves from the use of such disjointed units as described above? Surely, we are ready for motors whose output is in standard power units - watts. An important step would seem to involve NEMA. It would be useful if "MG-1" would include a section for the output of motors in SI units. Hopefully, they would 'start from scratch' and select one Series of Preferred Numbers. The selection of standard outputs of motors smaller than 1 kW could, in particular, be considerably improved over the fractional and milli- horsepower ratings now listed. By the way, doesn't it seem especially incongruous that a motor as modern as the HTS would be rated in such archaic units? ----- Original Message ----- From: "Duncan Bath" <[EMAIL PROTECTED]> To: "U.S. Metric Association" <[EMAIL PROTECTED]> Cc: <[EMAIL PROTECTED]> Sent: Saturday, 2001-10-20 09:51 Subject: [USMA:15726] IEEE per 2001-10 > I would like to send a letter to Power Engineering Review via an attachment. > I hope that it will get through OK and that this procedure will be > satisfactory to PER. > > DT Bath, 861 Kensington Dr., Peterborough ON K9J 6J8 > (705)743-4297 > > >
