General management of electrical equipment grounding and zero-connection provisions:
1, grounding: the power system or building electrical installations, facilities, certain conductive parts, through the grounding wire connected to the grounding pole.
2, work grounding (system grounding): in the power system electrical installations, for the operational needs of the grounding (such as neutral point directly grounded or grounded by other devices, etc.).
3, protective grounding: the metal casing of the electrical device, the frame of the distribution unit and line towers, etc., due to insulation damage may be electrically charged, in order to prevent it from endangering the safety of persons and equipment set up by the grounding.
4, lightning protection grounding: lightning protection devices (lightning rods, lightning lines and lightning arrester, etc.) to the earth to discharge lightning current and grounding.
5, anti-static grounding: in order to prevent static electricity on easy fuel oil, natural gas storage tanks and pipelines and other hazardous effects of grounding.
Expanded Information:
Set up by the operational needs of the power system (e.g. neutral grounding), so that under normal conditions there will be current flowing through the grounding electrode for a long period of time, but only unbalanced currents in the range of a few to several tens of amperes.
In the event of a ground fault in the system, there will be thousands of amperes of operating current flowing through the grounding electrode, however, the current will be removed by the relay protection device within 0.05~0.1s, even if it is a backup protection, the action is generally within 1s.
To eliminate the dangerous effects of overvoltage and grounding, such as lightning rods, lightning wires and lightning arrester grounding. Lightning protection grounding is only in the role of lightning impact will have current flow through, flow through the lightning protection grounding electrode of lightning current amplitude up to tens to hundreds of kiloamperes, but the duration is very short.
Earth potential, close contact with the earth and the formation of electrical contact with a conductive body or a group of conductors known as the grounding electrode, usually round steel or steel angle, but also can be used in copper rods or copper plate.
When the current flowing into the ground through the grounding pole to the earth as a hemispherical dispersion, due to the hemispherical sphere in the grounding pole from the closer the smaller, the further away from the larger, so in the grounding pole from the closer the larger the resistance, the further away from the smaller the resistance. Experimental evidence: in the distance from a single grounding pole or touch the ground outside of 20m, there is no actual resistance exists, the potential of the place has been close to zero.