Three-phase AC power is a power supply composed of three AC potentials with the same frequency, equal amplitude, and phase differences of 120° from each other. Three-phase AC power is widely used in daily life and industry.

In daily life, the single-phase alternating current we use is actually provided by one phase of three-phase alternating current. Three-phase AC power has many advantages, such as low manufacturing cost, material saving, simple structure, and excellent performance. In addition, three-phase AC has obvious advantages in power generation, transmission and distribution, and conversion of electrical energy into mechanical energy. For example, the capacity of a three-phase motor made of the same material is 50% larger than that of a single-phase motor. When transmitting the same power, a three-phase transmission line can save 25% of non-ferrous metals compared with a single-phase transmission line, and the power loss is lower. Single phase power transmission is less.

There are two main connection methods for three-phase AC power supply: star connection (Y-shaped connection) and delta connection (Δ-shaped connection).

Star Connection (Wye Connection): In a star connection, three sources or loads are connected together at each end to form a common point, often called the neutral point. Then, lead a wire from the other end of each power supply. These three wires are the three phase wires of the three-phase power supply. Star connections are commonly used for low-power equipment and household power. In a star connection, the relationship between line voltage and phase voltage is square root 3 times the relationship, i.e. U = √3 * U phase. The relationship between line current and phase current is equal.

Delta connection (delta connection): In a triangle connection, the first end of each power supply is connected to the tail end of the next power supply, forming a closed triangle. Delta connection is usually used where high voltage is required, such as electric motors. In delta connection, the line voltage is equal to the phase voltage, i.e. U = U phase. The line current is 3 times the root of the phase current, that is, I = √3 * I phase.

Each of these two connection methods has advantages and disadvantages. Which method to use needs to be chosen based on the actual situation and needs. When choosing a connection method, you need to consider factors such as the voltage, current, and power of the power supply, as well as factors such as the needs and safety of the equipment.