Electric utilities generate and distribute electricity using “three phase power.”
To understand “three phase power”, we need to understand phasors.
Phasor diagrams can be used to describe all AC voltages and AC currents.
“Three phase power” consists of three AC voltages that are connected together.
At each moment in time, each of the voltages is described by the real component of its vector in the phasor diagram.
This creates three sine waves that are offset from each other by 120 degrees.
Let’s call these “Phase A”…
“Phase B”…
And “Phase C.”
We can think of each phase as an AC voltage source and a light bulb.
Each light bulb represents several homes.
The phasor diagram describes the voltage of each of the three wires.
Phasor diagrams can also describe the current through each of the three wires.
The sum of the three currents is represented by the sum of the three vectors.
If the three light bulbs are identical, the sum of the three currents is always zero.
Since the sum of the three currents is always zero, we can remove the wires in the middle, and this will have no effect.
This allows us to deliver electric power using fewer wires.
Another advantage of three phase power is that it is much easier for electric generators to produce electricity if a steady constant output of power is required.
Although the power through each light bulb is constantly fluctuating,
the sum of the total power through all three light bulbs is always constant.
The total power will also be constant if
instead of connecting each light bulb between a line and the neutral,
we connect each of the light bulbs directly line to line.
In this example, the light bulbs are now connected line to line,
but the three coils of the electric generator are still connected line to neutral.
The voltages across the light bulbs are now larger than before,
because the “line to line” voltages are larger than the “line to neutral” voltages.
The “line to neutral” voltages are represented by the three small vectors, and the “line to line” voltages are represented by the three large vectors.
The “line to line” voltages are offset from the “line to neutral” voltages by 30 degrees.
Here, the “line to line” voltage waveforms are shown,
which are larger than the “line to neutral” voltage waveforms
by a factor of the square root of 3.
Here, the “line to line” voltage waveforms are shown, which are larger than the “line to neutral” voltage waveforms by a factor of the square root of 3.
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