Three-phase power generation and distribution refers to the use of three distinct alternating currents traveling through a power grid or piece of machinery as opposed to one. In figure 1, we see how most power generators in the United States work. Three separate coils are separated by 120 degrees as a rotating magnet generates a current inside the circuits. These three distinct alternating currents are carried along their own respective wires throughout the grid and are referred to as "Phase 1, Phase 2, and Phase 3" or "Hot 1, Hot 2, Hot 3". Heavy machinery or industrial areas can take advantage of all three phases for maximum power delivery with a smaller necessary current, and homes can utuilize only one phase. This gives the grid flexibility while minimizing line loss with higher total voltage delivery.

The setup of this generator and the three-phase grid allows for some very interesting properties. The first is that because each sin wave is offset by 120 degrees, the net voltage at any time "t" is zero. This means there is hypothetically no need for a neutral wire when all three phases are in use. This zero net voltage also reduces oscillation from a single alternating current in electronic equipment.

3-Phase power shares much of its historical narrative with AC. Its advantages, like AC power, were hotly debated in the "War of the Currents". In this era, famous scientists quarreled and publically discredited one another in an effort to determine if DC or AC should become the standard. Many involved parties held patents in their respective technology, and stood to make a huge sum of money if the world came around to their way of thinking.

George Westinghouse was one of these people. He strongly advocated for the AC standard, and held or purchased many of the patents surrounding three-phase power. Along with contributions from Galileo Ferraris, Mikhail Dolivo-Dobrovolsky, Jonas Wenström, John Hopkinson and Nikola Tesla, Westinghouse began work creating many of the machines and materials needed to distribute 3-phase alternating current nationwide in the 1880s.

To this day, three-phase alternating current is the standard in power generation and delivery.

Our power grid is set up similarly to figure 3, albeit much more complicated. To the left is a 3-phase generator, which creates three alternating currents traveling on three distinct lines phase-delayed by 120 degrees each. This creates three separate currents, and three separate "loads", which are represented by the multi-colored boxes on the right.

One load, for example, is able to connect to all three currents and take advantage of the maximum voltage from all three phases at any given time, giving it maximum power generation.

Load-balancing must occur on the grid so that one of the phases does not experience a disproportionately higher load. This, if not being motitored, may lead to out of phase currents or a non-zero net voltage.

Below we will explore the different configuration types of generators and transformers, and illustrate the different layouts grid connections can have.