Calculating 3 phase AC motor HP

Jul 26, 2008 61 Replies

| And a one=D vector space is a line, so all you have is + or - along this | line. Not what I would call a true vector space. Also note that when we use | normal AC analysis, we are in a 2D space.

That's because there will be some reactance in all by the most perfectly non-reactive case. Only if the reactance will never be anything but zero can you get away with using a 1D space. And using a 2D space still works, so it's not practically worth bothering with 1D.

| After all, a rms voltage doesn't actually exist and a real voltage is time | varying- hence the mathematical transform from a time varying sinusoid to a | complex number representation. | The actual voltage is in a 2 D space- one of which is time, while the rms | voltage is in a 2D space neither of which is time.

But when I look at JUST the voltage phase angle vectors, if they are all in

1D, then I can't get them out of 1D without employing some time base reactance (a real world example being a shaded pole motor).

You need to also multiply by 'root3' as there are three phases, then by the 'Power Factor', usually around 0.8 for a 7.5HP motor. This should make your calculation correct. Regards - Colin

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