The electric energy produced by the power plant is three-phase electricity. When the three-phase electricity is transmitted to the user end, a wire shall be led out from the center point (neutral point) of the three-phase line for grounding treatment. After grounding, a line is led out from this point and connected to the user's home. This line is called the neutral line (zero line). Take any one of the three phase lines, pass into the user's home, this line is called phase line (live wire). In this way, a single-phase power supply for household use is formed.
Experienced friends will find that if the neutral point is not grounded and a line is directly led out, which can also be used as a zero line, then why must the neutral point be grounded?
In an ideal state, the potential of the zero line is zero - what is a zero potential? Like temperature, there was no definite standard for this, so people defined the potential of the earth as zero. In other words, the potential of the zero line should be the same as that of the earth in an ideal state.
However, if the live wire in the line leaks, or the zero line produces induced charge, the potential of the zero line will rise, thus making the zero line charged. The so-called electrification means that the zero line is not zero to low voltage. When the potential of the zero line increases, the potential difference between the zero line and the earth will be generated, so the voltage between the zero line and the ground will be greater than zero.
At this point, touching the zero line that is not connected to the live wire will cause an electric shock (this is * critical). In addition, it will also cause a series of electrical failures, * obviously, the light flashes after the light is turned off.
After the zero line is grounded, once the potential of the zero line rises, but the zero line is connected with the earth, the potential of the earth will remain the same as that of the zero line, so as to avoid the above accidents.
Why must the zero line be carried out at the transformer end
As mentioned above, the grounding wire and zero line of the neutral point are led out from the neutral point. Why must it be conducted at the transformer end? Why can't the neutral line be grounded at the user's home?
There is a problem of electric shock on the live wire. The transformer belongs to the starting end of electricity consumption, and the user's home belongs to the terminal of electricity consumption. If the user touches the live wire at home and gets electric shock, the circuit formed at this time is terminal human body earth (distance from terminal to starting end) - starting end of circuit. If the zero line is grounded in the user's home, the circuit formed by the user's electric shock is terminal human body earth (distance from terminal to terminal) - circuit terminal.