We often only know that grounding can avoid personal electric shock. In addition to this effect, grounding can also avoid damage to equipment and lines, avoid fires, avoid lightning strikes, avoid static damage and ensure the normal operation of the power system.
(1) Avoid electric shock.
The impedance of the human body is greatly related to the situation of the environment. The more humid the environment, the lower the impedance of the human body and the simpler the electric shock. For example, people who have installed radios have been subjected to electric shocks, but they are all disconnected from the power supply because the environment is boring and the skin is boring. Grounding is a useful way to avoid electric shock. After the electrical equipment is grounded through the grounding equipment, the potential of the electrical equipment is close to the ground potential. Because of the existence of grounding resistance, the electrical potential of the electrical equipment always exists, and the grounding resistance of the electrical equipment is larger. When the attack occurs, the ground potential of the electrical equipment is also larger, and the risk of human touch is greater. However, if the grounding device is not provided, the voltage of the faulty device casing is the same as the phase-to-ground voltage, which is still much higher than the grounding voltage, so the risk is added accordingly.
(2) Ensuring the normal operation of the power system.
The grounding of the power system, also known as the work grounding, is generally grounded at the neutral point of the substation or substation. The grounding resistance of the working grounding is very small. A large grounding grid is required for the large substation to ensure that the grounding resistance is small and reliable. The purpose of the job grounding is to bring the potential between the neutral point of the grid and ground to near zero. The low-voltage power distribution system cannot avoid the phase line shelling or the phase line cracking and then hit the ground. If the neutral point is insulated from the ground, the voltage of the other two phases will be raised to 3 times the phase voltage, and the result may be the operation. Electrical equipment with a voltage of 220 burned out. For systems where the neutral point is grounded, even if one phase is shorted to ground, the other two phases can still be close to the phase voltage, so the electrical equipment connected to the other two phases will not be damaged. In addition, the vibration of the system can be avoided, and the electrical equipment and the line only need to consider the insulation level according to the phase voltage.
(3) Avoid damage from lightning strikes and static electricity.
In the case of lightning strikes, in addition to direct lightning, inductive lightning is also produced, and the inductive lightning is divided into electrostatic induction lightning and electromagnetic induction lightning. The most important method of all lightning protection methods is grounding.