What Are Electrical Phases?

What does it mean when a pump or a motor requires three phases of power? Is there some staging to how the power is delivered? Is it just another ‘useless’ statistic everyone already meets, like needing 120VAC for a toaster? Or is this something that’s really gonna rain on your HVAC Upgrade Parade?

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Our electrical power is delivered on Standards. We have a fixed expectation of what’s coming off the utility pole. In the US, that is generally Alternating Current, AC. The charge going through the wire Alternates between -1 and +1 60 times per second. We can look at this on a graph to understand it over time.

Phase1-01This gives us something like this. For a brief period of time, there essentially isn’t power flowing through the cable at all. For another brief moment, the current will flow in reverse, and finally it flows forwards. This is Single Phase power. It’s power moving through one conductor, one wire.

Electricity like this is perfectly fine if you want to power your kitchen blender or power a heating element. In general, single phase power will work for most household and office applications without a single problem. The downsides don’t appear in day to day equipment.

On higher end or heavy duty equipment however, those momentary periods where there’s no power flowing through the cable are a gigantic problem. Just imagine, for a fraction of a second, a motor is slowing down, the speed is inconsistent because of the varied power. At the same time, there’s some additional hardware required to start a single phase motor. There’s less power available as well, one conductor can only push so much current.

Two Phase

We can add a phase to change how the equipment performs and to deliver more power. Generally speaking, most houses in the US have 2-Phase power delivered, but are only wired to use one of those phases. Phases can be added to increase the overall voltage, such as providing 240 Volts for driers and furnaces, at the residential level.

Phases-2-01

When we add that second phase, a conductor but with its current slightly offset, we start to extend how long the power flows in a direction without reversing or becoming zero. For an electrical motor, this means more power. The problem is, is that power is still not consistent. There’s a large gulf we’re going to fall into when the power inverts between positive and negative.

This gap is a problem for performance. That inversion point can cause variations in motor speed with some rough and rapid changes. We’re not at that sweet spot of performance against ludicrous cost, but we’re close.

3 Phases

Phases-3-01.png

Now we have constant power delivery. This isn’t like DC Power either. There is a constant flow of power, but unlike in a DC situation, there’s variation. When 3 Phase Power is put into an electric motor, the phases are all different. The windings in the stator are producing different electrical fields. These fields move with the current, causing the electrical force to naturally ‘spin’. This gives us a motor that can have near constant performance, does not need any additional hardware to start it, and because there’s  three conductors, and three phases, we’ve essentially trippled our performance by adding only one or two wires to a ‘stock’ single phase setup.

These benefits do transcend motors, though they are the key example where you’ll see “3 phase required.” There are datacenters which use 3 phase power to provide smoother and more efficient power. There’s electrical equipment which uses it to run at higher voltages.

Chances are, if you’re in a multi-phase situation, you already have multiple phases wired up. If you don’t have multiple phases already, then they probably aren’t needed. If you’re told you need a “3-Phase” anything, remember that you probably can’t just jump back to single phase without some drawbacks.

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