How To Convert Three Phase Electricity into Two-Phase Electricity? Wiring Method of Three-Phase Electrical to Two-Phase Electrical (3)
1. The difference between three-phase power supply and single-phase power supply：
The power generated by the generator is all three-phase, and each phase of the three-phase power supply and its neutral point can form a single-phase loop to provide users with powerful energy.
Note that the AC circuit cannot be called positive or negative, it should be called the line terminal (called the live wire in the civil electricity) and the neutral wire (called the neutral wire in the civil electricity).
2. According to regulations, the neutral point of the 380-volt (three-phase) civil power supply should not be grounded at the incoming end. Grounding at the transformer end, this grounding is to take into account that the floating-point cannot cause a point higher than the power supply voltage. There is a certain resistance in the ground between the grounding of the user end and the grounding of the transformer end. The power supply method is a live wire and a neutral wire, the neutral point lead wire forms a loop, and a ground wire is connected to the single-phase three-core power jack.
This is taking into account the realization of the leakage protector function. The working principle of the leakage protector: if a human body touches the wire end of the power supply, that is, the live wire or there is leakage inside the electrical equipment. At this time, the current flows from the live wire to the earth through the human body or the casing of the electrical equipment but does not flow through the neutral wire, and the current of the live wire and the neutral wire will not be equal. After the leakage protector detects this part of the current difference, it will trip immediately to protect the safety of people and electrical appliances. Generally, this differential current is selected at tens of milliamps. If the neutral point of the power supply is directly grounded, this is not allowed in civil power construction, and the leakage protector will lose its function and cannot protect the short circuit of personal and electrical equipment.
3. The concept of "three-phase electricity" is: that when the coil rotates in the magnetic field, the wire cutting the magnetic field line will generate an induced electromotive force, and its variation law can be represented by a sine curve. If we take three coils, place them 120 degrees apart in space. The three coils are still rotating at the same speed in the magnetic field, and three induced electromotive forces with the same frequency must be induced.
Since the three coils differ by 120 degrees in spatial position, the generated current is also a three-phase sinusoidal change, which is called a three-phase sinusoidal alternating current. Industrial electricity uses three-phase electricity, such as three-phase AC motors.
The voltage between any two phases is 380VAC, and the voltage between any two phases is 220VAC. Divided into A phase, B phase, and C phase. The lines are represented by L1, L2, and L3. (Three-phase alternating current also has 660VAC and 6000VAC power supply due to different uses).
3.1 Generators that can generate potentials with equal amplitude, equal frequency, and 120° phase difference are called three-phase generators. Using a three-phase generator as a power source is called a three-phase power source. A circuit powered by a three-phase power supply is called a three-phase circuit. U, V, and W are called three-phase, and the voltage between the phases is the line voltage, and the voltage is 380V. The phase voltage between the phase and the centerline is called the phase voltage, and the voltage is 220V.
3.2 Three-phase electrical load connection
Divided into delta connection and Y connection.
The load lead of the delta connection method is three live wires and one ground wire, the voltage between the three live wires is 380V, and the voltage of any live wire to the ground wire is 220V.
The load lead of the Y-shaped connection is three live wires, one neutral wire, and one ground wire. The voltage between the three live wires is 380V, and the voltage of any live wire to the neutral wire or to the ground wire is 220V.
The total power of three-phase electrical appliances = voltage of each phase × current of each phase × 3, that is, total power = current × voltage (220V) × 3 (W = U × I × 3).
3.3 There are three types of three-phase electric meters: mechanical meter, ordinary electronic meter, and magnetic card electronic meter. The general specifications are: 1.5(6), 5(20), 10(40), 15(60), 20(80), 30(100) (voltage 3×380/220V~).
Note: The load of the electric meter can be matched with the inductive coils of different transformation ratios to meet the usage requirements. For example, if a meter with a specification of 3x1(2)A is used for distribution inductance coils, and the inductance coil transformation ratio is selected as 1:50, the maximum rated current that can be carried by each phase is 100A.
