In these large cities in the east and south, electricity consumption is high and the local electricity supply is far from sufficient. Therefore, electricity can only be transmitted from west to east and from north to east. south. Therefore, the east-west extent and the north-south extent are large and the distance is too far. The standard voltage 220V/380V electricity used to send to these cities cannot be used by users and industries once it arrives at its destination. The long-distance transmission process will be greatly affected by losses, so the only way to solve long-distance power transmission is to increase the voltage. Since high voltage power transmission increases the voltage and then sends it to the destination, this means that no electricity is needed during the journey to the destination.
Whether it is a thermal power plantor a hydroelectric plant, the electricity produced is three-phase, three-wire electricity. For long distance transportation, the voltage must be increased via a booster station, with the. the purpose of transporting electricity to the destination. In this process, domestic electricity and industrial electricity are not taken into account, so there is no need to use a neutral line. On the surface it is about saving materials, but in reality it is about reducing costs as much as possible.
Once the high voltage electricity reaches its destination, a step-down transformer is needed to reduce the voltage. At this point, not only civil and industrial electricity must be taken into account, but also electrical safety. Since the neutral line and ground wire are only considered in the 380V/220V low-voltage distribution network, the general electrical power supply methodselectrical in the low voltage distribution network include a three-phase four-wire system and a three-phase five-wire system. Therefore, a line is drawn from the neutral point of the secondary side star connection of the step-down transformer in the low voltage distribution network, i.e. the neutral line. At present, the neutral line and one phase of the three-phase power supply have a phase voltage of 220V, and the line voltage of the two lines of the three-phase power supply is 380V. It can be used not only for civilians but also. industrial use.
The three-wire and four-wire power supply method has only one neutral wire and no ground wire, which can prevent the neutral wire from being electrified due to three unbalanced phases. The three-phase five-wire power supply method has a neutral wire and a ground wire. The ground wire at this time can guarantee the user's electricity reliability. VSHowever, the neutral wire and the ground wire must be wired repeatedly to prevent the neutral wire from being open circuited and causing the neutral wire to be electrified and accidentally injure people.
Both answers above are one-sided. I work in a power plant. I can explain to you: First of all, the electricity produced by general power plants is currently three-phase (divided into three phases: A, B and C). Each phase is 120 degrees (one). circle) different from each other in space. 360 degrees, one phase occupies 120 degrees of space), and the three phases are live wires.
We all know that to have water flow, there must be water pressure, so if there is current, there must be voltage. Only if there is a live wire and a neutral wire will there be voltage. If there is only one live wire, who makes the difference? As indicated by his name,the potential of the neutral wire is zero, that is, it is connected to earth. When the potential of the live wire is positive, current flows out of the live wire through the load and back to the power supply. power supply via neutral wire; When the potential of the live wire is negative (i.e. the potential is currently less than zero), current flows from the neutral wire, through the load, and back to the power source via the wire under pressure. . It can be seen that even though the zero line potential is still zero, that does not mean it is useless.