Three-phase electricity, namely three-phase alternating current, is a form of transmission of electric energy. Three-phase AC power supply consists of three AC potentials with the same frequency, equal amplitude and phase difference of120. The concept of "three-phase electricity" is that when the coil rotates in the magnetic field, the conductor cuts the magnetic field lines, which will produce induced electromotive force, and its changing law can be expressed by sine curve.
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The following is the ideal mathematical formula of three-phase AC voltage:
V 1=Asin(2πft)=Asin(wt)
V2 = Asin (2πft-2π/3)= Asin (wt-2π/3).
v3 = Asin(2πft+2π/3)= Asin(wt+2π/3)
Where a is the peak voltage and f is the frequency of AC voltage.
The voltage between phases is called line voltage, the voltage between any two phases is 380V V, the voltage between phases and neutral point is called phase voltage, and the voltage between any relative neutral point is 220V V V (three-phase alternating current is supplied by 660V and 6000V respectively for different purposes, etc.). ).
A generator that can generate an electric potential with equal amplitude and frequency and a phase difference of 120 is called a three-phase generator. A three-phase generator is called a three-phase power supply; A circuit powered by a three-phase power supply is called a three-phase circuit.
Three-phase connection: divided into triangle connection (symbol △) and star connection (also known as Y connection, symbol Y).
The load leads connected in a triangle are three live wires and one ground wire, the voltage between the three live wires is 380V, and the voltage between any live wire and the ground wire is 220 V;
The load leads of Y-shaped connection are three live wires, a zero wire and a ground wire. The voltage between three live wires is 380 volts, and the voltage between any live wire and neutral wire or ground wire is 220 volts ... The figure shows an example of Y-shaped connection. All six light bulbs are turned on. When three phases are balanced, the neutral current is zero. When unbalanced, the zero line is maintained at zero potential, and there will be current on it.
The difference between three-phase power supply and single-phase power supply: single-phase is 220V, which is the voltage between phase line and zero line. The three-phase voltage is 380V between A and B A.B.C, and the electrical appliance is a three-phase 380V motor or equipment. The power generated by the generator is three-phase, and each phase of the three-phase power supply and its neutral point can form a single-phase loop to provide electricity for users. Note that the AC circuit here can't be called positive or negative, but should be called phase line (civil electricity is called live line) and zero line (civil electricity is called zero line).
References:
Three-phase electricity-Baidu encyclopedia