Three-phase electric power
Three-phase electric power is a method to generate, transmit and distribute AC electricity. It is the most common method in power systems to transfer power from generation to load. Three-phase systems are usually more economical to be used than equivalent single-phase or double-phase systems.
Three-phase Electric Power Media
Three-phase transformer with four-wire output for 208Y/120 volt service: one wire for neutral, others for A, B and C phases
The first AC motor developed by Italian physicist Galileo Ferraris. This was a two-phase motor and required four wires.
Three-phase electric power transmission lines
Three-phase transformer (Békéscsaba, Hungary): on the left are the primary wires and on the right are the secondary wires
Wye (Y) and delta (Δ) circuits
A delta-wye configuration across a transformer core (note that a practical transformer would usually have a different number of turns on each side).
A transformer for a "high-leg delta" system used for mixed single-phase and three-phase loads on the same distribution system. Three-phase loads such as motors connect to L1, L2, and L3. Single-phase loads would be connected between L1 or L2 and neutral, or between L1 and L2. The L3 phase is 1.73 times the L1 or L2 voltage to neutral so this leg is not used for single-phase loads.
Three-phase AC generator connected as a wye or star source to a wye or star connected load
