Introduction of three-phase AC circuit

Important knowledge Three-phase AC power supply: It is composed of three single-phase AC power supplies in a certain way. The single-phase AC power supplies must have the same frequency, the same amplitude and the phase difference 120o in turn. Three-phase three-wire system: the ends of three stator windings of a three-phase alternator are connected together, and three live wires are led out from the beginning of the three windings to supply power to the outside, and there is no center line. That is, a star connection without a neutral line. Three-phase four-wire system: a mode formed by connecting the neutral points of three-phase power supply and three-phase load with wires. Three-phase five-wire system: refers to live wire A, live wire B, live wire C, neutral wire N and PE wire, in which PE wire is a protective ground wire, which is specially used to connect equipment housings. Ensure the safety of electricity use. 1 Return to the important knowledge point: star connection (Y): the connection mode in which the negative poles of three power supplies are connected together to form a node (neutral point N) and three output lines (live wires A, B and C) are led out from the positive poles of three power supplies. Triangular connection (δ): Three power supplies are connected in sequence, that is, the positive electrode is connected to the negative electrode, and the negative electrode is connected to the positive electrode to form a triangular loop, and then three connecting wires are led out from each connection point. Safe voltage: Voltage that won't cause harm to human body in a certain period of time. 2 Important knowledge points Single-phase electric shock: refers to electric shock caused by single-phase 220V alternating current (civil electricity). Most electric shock accidents are single-phase electric shock accidents. Two-phase electric shock: an electric shock accident in which the human body touches two charged bodies at the same time. At this point, the human body will suffer

380 volts

Line voltage is generally more dangerous than single-phase electric shock. Step-by-step voltage electric shock: people or livestock stand within 8 ~ 10 meters from the falling point of the conductor, resulting in electric shock accident. 3 important knowledge points protection grounding: prevent the metal shell of electrical device, the frame of power distribution device and the line tower from being charged, endangering personal and equipment safety.