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I am reading though a product manual for an amplifier that I am working with. It says that if you view the motor Back-EMF while it is disconnected from the controller and spun in a clockwise direction you should see the following outputs:

enter image description here

can someone tell me why the phases are only 60 degrees apart? I thought for a balanced, 3-phase system (which these motors are) the phases were supposed to be 120 degrees apart:

enter image description here

does it have anything to do with the fact that they are referenced from the same phase? If so, could someone show me how this mathematically works out?

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  • \$\begingroup\$ those are not phases, they are line voltages \$\endgroup\$ – JonRB Jul 18 '14 at 19:00
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Try this: -

enter image description here

I've stolen the OP's picture and named the three primary phasors W, V and U.

I've also drawn two new phasors namely W-U and V-U.

Those two phasors are 60 degrees apart if W, V and U are exactly 120 degrees apart and of equal magnitude.

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  • \$\begingroup\$ Thank you for this. I discussed it with some of the engineers around here as well and got the same response. It is due to the fact that they are referencing the two faces with respect to another phase instead of ground. Using some vector math you can arrive at this solution. \$\endgroup\$ – mayfield512 Jul 21 '14 at 14:58

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