What the Heck is Three-Phase Power (and how can you get some)?

AIR COMPRESSOR MOTOR


Vin Marshall


I recently moved my shop, and in addition to the big issues, from forklift rental to sleep deprivation, we also had to deal with things like three-phase power, a variation of power delivery often used for big equipment. The old shop had it and the new shop doesn't. So what the heck is three-phase power and how can you convert machinery to go from the more common single-phase to three-phase and vice versa? Read on.

For us, the impact was limited because only the air compressor had a three-phase motor. Some of the welding equipment had been running on three-phase, but can easily be re-configured to run on either three-phase or single-phase.

But first, a short explanation of three-phase power.

Alternating current does just as it's name implies and alternates cyclically, first flowing in one direction in a circuit and then reversing to flow in the other. As it does this, the magnitude of the voltage supplied varies continuously between a positive and negative maximum amplitude. In the US and anywhere else with 60Hz power, this cycle happens 60 times per second. Picture a sine wave: The amplitude of the supplied voltage passes through zero twice per cycle, and at those moments the power supplied is nada. While this doesn't matter to many electrical appliances, it has significant implications on larger equipment—particularly motors.

Three-phase power provides three alternating currents—essentially three separate electric services—uniformly separated in phase angle. That is, the points in time at which each leg of alternating current reaches a maximum voltage are separated by 1/3 of the time in a full cycle. What this means practically is that the total amount of power supplied by all three alternating currents remains constant. The three phases share a common neutral leg in most installations.

Read More at :
https://www.popsci.com/diy/article/2009-10/three-phase-power-and-how-get-it

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