The sum of the grounding resistance of the grounding body or natural grounding body and the grounding wire resistance is called the grounding resistance of the grounding device. The grounding resistance value is equal to the ratio of the grounding device voltage to the ground and the current flowing into the ground through the grounding body. The grounding resistance obtained by the impulse current flowing into the ground through the grounding body is called impulse grounding resistance; The resistance obtained by the power frequency current flowing into the earth through the grounding body is called the power frequency grounding resistance.
When the power equipment has grounding fault, the potential difference between the grounding part and the ground zero potential point is called the grounding device to ground voltage or grounding device potential.
Possible consequences of poor grounding
1. Broken strand and virtual connection of grounding wire easily cause the grounding wire to be burnt by high current or the printed grounding resistance to be large, resulting in poor grounding current. The quality inspection of the two does not form a loop, so that the high potential at the high voltage side of the transformer cannot be directly grounded. In addition, maintenance personnel sweat more after work, the surface resistance of the human body decreases, and the potential on the transformer is quickly led to the ground through the human body. If it is a fatal current, it will cause casualties to maintenance personnel.
2. When repairing the transformer or high-voltage line, no grounding wire is installed on the secondary side. If the electric welding machine or other mobile power generation equipment is used on the secondary side, it is easy to cause the secondary side to return power and increase the induced voltage on the primary side of the transformer. Current increase; If someone works on the transformer, the return voltage is high and the current is large, which is easy to cause injury to personnel.