Three-phase power is a common method of alternating current electric power generation, transmission, and distribution. It is a type of polyphase system and is the most common method used by electrical grids worldwide to transfer power. Three-phase systems use less conductor material to transmit electrical power than equivalent single-phase systems at the same voltage.

In a three-phase system, three circuit conductors carry three alternating currents (of the same frequency) which reach their instantaneous peak values at different times. Taking one conductor as the reference, the other two currents are delayed in time by one-third and two-thirds of one cycle of the electrical current. This delay between phases provides constant power transfer.

Star (Wye) Connection: In this configuration, one end of each winding is connected to a common point called the neutral. The line voltage is √3 times the phase voltage, while the line current equals the phase current. This connection is commonly used for power distribution as it provides a neutral point for single-phase loads.

Delta Connection: In this configuration, the windings are connected end-to-end, forming a closed loop. The line voltage equals the phase voltage, while the line current is √3 times the phase current. Delta connections are often used for high-power industrial motors and transformers.