The working ground is set by the operation needs of the power system (such as neutral grounding). Therefore, under normal conditions, there will be current flowing through the ground electrode for a long time, but it is only an unbalanced current of several amperes to tens of amperes. When a ground fault occurs in the system, thousands of amperes of working current will flow through the ground electrode, but this current will be cut off by the relay protection device within 0.05~0.1s. Even for backup protection, the action is generally within 1s.
Lightning protection grounding is to eliminate the dangerous effects of overvoltage, such as the grounding of lightning rods, lightning conductors and lightning arresters. Lightning protection grounding will only flow under the impact of lightning. The amplitude of the lightning current flowing through the lightning protection grounding electrode can reach tens to hundreds of kiloamps, but the duration is very short.
Protective grounding is to prevent the equipment from endangering personal safety due to insulation damage and charging, such as the metal shell of electrical equipment. Protective grounding will only flow current when the equipment insulation is damaged, and its value can vary within a relatively large range.
When current flows through the above three ground electrodes, the potential of the ground electrode will rise, which will lightning protection affect the safety of people and equipment. For this reason, the potential rise of the ground electrode must be limited, or corresponding safety measures must be taken to ensure the safety of equipment and personnel.
The difference between lightning protection grounding and electrical grounding:
1. Protective grounding refers to the connection of the non-charged metal part of the electrical device with the grounding device under normal conditions to prevent the part from being charged suddenly and causing harm to the human body.
2. Working grounding is to ground the neutral point of the transformer. Its main function is the stability of the system potential.
3. The down conductor of the PE wire protective grounding should be connected to the ground electrode separately. The distance between the down conductor of the PE wire and the lightning protection down conductor is as far as possible. It is required that the lightning current enters the ground along the lightning protection down conductor. , Let the lightning current flow into the ground, it will not spread from the down conductor of the PE wire to the equipment shell.