Skipper - 8/21/2010 08:45
Motor shop is going to hook up a rotary converter to this next week but I was curious.
Have read about a "wild" leg (think thats what its called) that MIGHT be a different voltage than the 120. Seems as though you don't want that leg running any 110 application if there are motor controls that are 110. If true is that leg differentiated some way other than 3 like wires coming off line to a main? This is a drill press that has a disconnect box still wired in that 3 wires go through fuses and a 4th to ground.
So the 240 lines are phased / timed to each other some way? Does that have something to do with the 60hz?
Yes it is all in the timing. How's your math? AC votage runs in a true sin wave with equal time spent below ground and above ground. When you measure AC voltage you are not measuring true voltage but instead something called RMS which if I remember correctly stands for root mean average.
Always remeber voltage is relative. Just because you have a 120v circuit doesn't mean your reference (ground) is always 0 volts. If you have a reference or ground level set at 120 volts and your leg is running at 240v you still have a 120v circuit. This is used a lot when working with DC logic circuits.
So for 3 phase you have 3 legs with each one running a sin wave of voltage into your motor. For 3 phase to work properly each leg has to be 120 degrees out of phase from the other 2.
This is the timing part. Your sin wave of voltage over time runs (lets use a 230 v circuit) from +230v to -230v to complete a cycle. For 60hz this cycle occurs 60 times/second. If you were running at 1hz then every third of a second one of the legs would be at max voltage.
Clear as mud?
Edited by Cowpoke 8/21/2010 11:50
 (3 phase sin wave.bmp)
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 3 phase sin wave.bmp (32KB - 43 downloads)
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3 phase electrical question
