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Posted by Joe Scina (144.160.5.82) on June 04, 2002 at 13:37:59:
In Reply to: Three Phase Power posted by Johnny Potato on March 05, 2001 at 15:38:00:
If 415 were your line to line voltage then your phase voltage would actually be 240. The square root of 3 is derived from a phasor triange. If you divide 360 by 3 (three phase) you get 120 degrees. If you take two sides of a triangle that are 240 and have an angle between them of 120 degrees you will geometrically get the third side of 415. This is were the relationship of square root of three is proven.
The most common three phase voltages are phase of 120 and line to line of 208. Notice the root of three again (1.73) relationship. 480 line to line and 277 are common in industry. Three phase power has two main advantages: it's power does not pulsate like your typical single phase. This is particularly important in large industrial motors where the added vibration will wear out the motor bearings quicker if single phase were used. Secondly you can deliver more power per pound of metal. I would go into detail about this but you are obviously simple minded. Try taking some courses if you are really interested.