Tag Archives: motor

3PH Means 3PH


Now I remember.  After hooking up the hydro (Ca-nay-dee-en for electricity) I was toying with the Variable Frequency Drive (VFD) and something twigged.  This is a three-phase motor and was hooked up to a three-phase source of power…and this is a three phase-to-three phase VFD.  Nowhere in this region is three-phase available.  And now the words come back…it’s just something I remember from when we picked it up…you’ll need three phase…you do have three phase don’t you?  Um.  I guess not…no.  No we don’t have three phase.  SO…there’s no way for the motor to run?  The answer is yes, there certainly is.  A couple of ways in fact.

Phase in electricity describes the method used behind the rapidity of the back-and-forth motion of electrons in alternating current (ac) which creates the power.  Typically our lights, appliances, and motors in our homes are single phase.  That means that a single wave of electrons moves back and forth, with waxing power and waning power as the wave accelerates and decelerates, stops and reverses itself.  This works well for typically lower-powered devices.  But when a larger, industrial motor is working, it works better either on direct current (dc), which is a high-maintence machine, or else by splitting the current into three waves, which overlap themselves by a third, thereby maintaining a more constant pressure presented to the motor.  Current capacity in three phase is three times that of single phase.

A dc motor is out of the question for this loom application.  The truly great news is that it is totally possible to convert single phase to three phase with the right VFD!

Using a rectifier to convert single phase ac into dc power, a power inverter of three semiconductor switches to produce square waves at 0, 120, and 240 degree stages, giving a constant power to the motor.

This 6 hp motor only uses 6 amps.  So, I disconnected the old three phase VFD and put in an order for a new one.

I figured all this out after getting up at 4:30, taking the dogs for a run, reading, writing, finishing prepping more ground for a new seedbed of brome grass, running the dogs, eating a quick lunch, and completing the electricity in the weaving shop.