The three live wires are three-phase asynchronous motors and do not need to be connected to zero.
In the case of a three-phase balance, we will obtain a neutral point potential. This potential does not change periodically like the three phases, but is a constant value. Then we simply borrow from the fact that the Earth is an equipotential body.
And set the potential of the neutral point above to be at the same potential as ground (the generator neutral point is grounded), then this line (neutral line) can be omitted. When you need to use the neutral wire, simply pull one wire straight from the ground. This is why high voltage lines do not need neutral wires.
Detailed information
The two wires of the lighting circuit, one is called live wire and the other is called neutral wire. The difference between live wire and neutral wire is that they have voltages ddifferent with respect to earth: the voltage of the live wire with respect to earth is 220 V and the voltage of the neutral wire with respect to earth is 0. The earth wire is the earthed wire. If there is no neutral wire in the electrician's house, it is usually a three-hole outlet, not a three-phase outlet.
There is a ground wire in the middle and live wires and neutral wires on both sides. Typically, outlets in the home are three-hole outlets instead of neutral (N) lines.
The difference between the live wire and the neutral wire is that their voltages to ground are different: the voltage of the live wire to ground is 220 V and the voltage of the neutral wire to ground is 220 V. 0. The neutral wire is the line drawn from the neutral point of the generator or power transformer. If it is not grounded, it is called neutral line. If it is properly grounded (the ground is at zero potential), the linene neutral to. this time is also called the neutral line.
Although the neutral wire and the earth wire of civil electricity are drawn from the same point, their respective functions are distinct and cannot be mixed. For example, the neutral wire and the live wire are the electricity return lines.
They are connected to the housing of the electrical appliance, and the current flowing through the wires is the same, so the diameters of the wires have the same thickness. The ground wire is connected to the housing of the electrical appliance. When the electrical device breaks down, current flows through it. Generally there is no current, so the wire diameter is much thinner. The neutral wire and the live wire are electrical circuits, so the neutral wire should not be connected to the shell, as this will cause an electric shock.
Ground wire, neutral wire and live wire: Earth is a good conductor and the earth wire is short circuitedconnected to the earth via deeply buried electrodes. Mains power is transmitted in a three-phase manner and has a neutral wire. When the three phases are balanced, the neutral wire current is zero, commonly called "neutral wire". Another characteristic of the neutral wire is that. it is in the general distribution of the system with the earth wire that the electrical input is short-circuited and the voltage difference is close to zero.
Baidu Encyclopedia - Three-phase asynchronous motor
The neutral wire of the three-phase alternator is not grounded. Why does the live wire have a voltage of 220 V at. Earth ? If one of the live wires is touched at this time, it will be an electrical person?
The live wire is the power wire that carries electricity in a circuit. The neutral line is the line drawn from the neutral point (N) on the secondary side of the transformer. It forms a loop with thephase line (L) for powering electrical equipment.
1. Use color to distinguish: In the power cable, green, red represent phase A, phase B, phase C (three-phase live wire) and blue respectively.Color represents neutral line and colors yellow and green represent the ground wire.
2. Use an electric pen to distinguish: the neon tube will glow when the live wire is tested with an electric pen, but the neutral wire will not.
3. Use a voltmeter to distinguish: the voltage between different phase wires (that is, live wire) is the line voltage 380V, and the voltage between phase wires (live wire) and the neutral wire (or a good grounding body) is The phase voltage is 220 V and the voltage between the neutral line and a good ground is 0 V.
The live wire and the neutral wire touches each other
Since the voltage between thetwo is equal to 220 volts and the resistance between the two contact points is almost zero, the current at this level The time is very long. Tremendous heat will be generated at the point of contact with the neutral wire, causing an electric spark. The temperature at the spark will be high enough to melt the metal wire. If the human body contacts the live wire and the neutral wire at the same time, regardless of whether it touches the ground at the same time, it will receive an electric shock (called double-wire electric shock).
Reference for the above content: Baidu Encyclopedia - Live Wire
In domestic circuits, there is a voltage of 220 V between the live wire and the earth. Why is there a voltage of 220 V between the live wire and ground. not a neutral wire?
1. If the neutral wire of the three-phase alternator is not grounded, the live wire will have a small voltage to ground, but there is nodoes not have 220 V. Touching one of the live wires will not cause a shock. anybody.
2. When the neutral line of the three-phase alternator is not grounded, the winding will not burn if grounded at one point. Only if there are more than two grounding points will the winding do this. be burned.
3. According to regulations, the zero line (neutral line) of a three-phase alternator must not only be grounded, but the grounding resistance must be qualified to ensure the safe and normal operation of the three-phase alternator. Generator.
If you study circuits at home in junior high school physics classes, when you solve problems, you can answer them according to the formulas of DC circuits.
There are many things about AC that you will understand in the future. You may not understand them now, but I'll send them to you to throw un eye.
Principle of three-phase alternating current
1. The difference between three-phase power and single-phase power: The power generated by the generator is three-phase, and each phase of the three-phase power is linked to one of them. These points can form a single-phase loop to provide power to users. Note that in the AC circuit here, it cannot be called the positive pole or the negative pole. It should be called the end of the line (called live wire in civil electricity) and the neutral line (called neutral line in civil electricity).
2. According to regulations, the neutral point of a 380 volt (three-phase) civil power supply must not be earthed at the input (it is earthed at the end of the transformer. This earthing earth is taken taking into account that this cannot be caused by the floating point Caused by the point higher than the supply voltage.on, there is some resistance between the user end ground and the transformer end ground in the earth). The method is one live wire and one neutral wire (neutral point conductor wire) forming a loop. There is also a ground wire connected to the 3-phase power jack. This takes into account the achievement of the function of the leak protector. (The working principle of the leakage protector is: if a human body touches the end of the power supply, that is, the live wire, or if there is a leak at the Inside the electrical equipment, current flows from the live wire through the human body or the shell of the electrical equipment. If the earth does not pass through the neutral wire, the currents in the live wire and the neutral wire will be unequal. .The detector detects this current difference and triggers immediately to protect the safety ofpeople and electrical appliances. Generally, this differential current is selected in tens of milliamps.) If the neutral point of the power supply is directly grounded (this is not allowed). civil electrical construction), the leakage protector loses its function and cannot protect people and electrical equipment from short circuits.
Three-phase electricity can be used for lighting. Three lamps are star connected, that is, any wire of each lamp is interconnected and the other wire of each lamp is connected to three-phase wires. A loop is formed. The voltage between two three-phase power lines is 380 volts, and the voltage between each phase and ground is 220 V.
Three-phase electricity has three live wires and two. -three-phase phase with two live wires. , in my ancient memory, there seems to be only one live wire (sweat), what are so many wires forou voltage?" The poster will understand, provided you analyze and read. the following answer:
(3) The concept of "three-way electricity" is as follows: Let's be more precise. We know that when the coil rotates in the magnetic field, the wire cuts the line of the magnetic field. generate an induced electromotive force. Its pattern of change can be expressed by a sinusoidal curve, this will be the case Their spatial positions are 120 apart. degrees and the three coils always rotate at the same speed in the magnetic field, and three electromotive forces induced with the same frequency will be induced. The current is also a three-phase sinusoidal change, called three-phase sinusoidal alternating current. three-phase electricity, such as three-phase AC motors
The voltage between two phases is 380 VAC The voltage between one phase and the other is 220 VAC. A, phbase B and phase C. It is represented by L1, L2. and L3 on the line (three phase AC power also has 660VAC and 6000VAC depending on usage
1.1 A generator capable of generating potentials with equal amplitudes, equal frequencies and a phase difference of 120° is called a ). three-phase generator; a three-phase generator as a power source is called a three-phase power supply; a circuit powered by a three-phase supply is called a three-phase circuit. three phases. The voltage between phases is 380 V. The voltage between phases is called phase voltage and the voltage is 220 V. >
2.1 The connection method of three-phase electric load
is divided into a triangle. connection method and Y-shaped connection method.
The load wires of the triangular connection method are made of three live wires and one ground wire, the voltage between the three wires under voltage is 380 V and thetension between any live wire. and the ground wire is 220V;
The load wires of the Y-shaped connection consist of three live wires, a neutral line and a ground wire. The voltage between the two wires is 380V and the voltage between any. the live wire and the neutral wire or the earth wire is 220V
The total power of the three-phase electrical appliance is equal to the voltage of each phase multiplied by the current of each phase then multiplied by 3. .Total power = current × voltage (220 V) × 3 (W = U × I × 3)
2.2 Three-phase electric meter There are three types of three-phase electric meter: mechanical meter, ordinary electronic. counter and electronic counter with magnetic card. The general specifications are: 1.5(6), 5(20).), 10(40), 15(60), 20(80), 30(100) (voltage 3×380/220V~).
Note: The electric meter load can be adapted to inductance coilsof different transformation ratios to meet usage requirements. For example, if an electric meter with a specification of 3x1(2)A is used with an inductor coil and the inductance coil ratio is selected at 1:50, the maximum current rating that each phase can carry is of 100 A.