As the name suggests, lightning protection is to prevent direct or side strikes from lightning, and grounding is to introduce lightning current into the ground. Electrical grounding is divided into protective grounding and working grounding. Protective grounding is to prevent the device from leaking electricity from causing an electrical shock to the case, and introduce leakage current into the ground. The working ground is for the normal operation of the equipment. The neutral point is directly connected to the ground to form a zero potential point (such as a transformer).
Earthing (earthing) Grounding refers to the neutral point of power systems and electrical devices, exposed conductive parts of electrical equipment and external conductive parts of devices are connected to the earth through conductors. Can be divided into working ground, lightning protection ground and protective ground.
The working ground is set by the operation of the power system (such as neutral grounding), so under normal conditions, there will be a long-term current flowing through the ground electrode, but only an unbalanced current of several amps to tens of amps. When a ground fault occurs in the system, thousands of amperes of working current will flow through the ground electrode. However, this current will be cut off by the relay protection device within 0.05 ~ 0.1s. Even in the case of backup protection, the action is generally within 1s.
Third, lightning protection grounding
Lightning protection grounding is the grounding designed to prevent the danger of overvoltage, such as the grounding of lightning rods, lightning conductors and arresters. Lightning protection grounding will only flow current under the effect of lightning strikes. The magnitude of the lightning current flowing through the lightning protection ground electrode can reach tens to hundreds of amperes, but the duration is short.
Fourth, protective ground
Protective grounding is to prevent the equipment from endangering the human body due to insulation damage and electrification, such as the metal shell of power equipment, reinforced concrete poles and metal pole towers. Protective grounding can only cause current to flow if the insulation of the equipment is damaged, and its value can vary within a wide range.
When the current flows through the above three types of ground electrodes, the potential of the ground electrode will increase, affecting people and equipment. To this end, the potential of the ground electrode must be limited, or appropriate measures must be taken to ensure equipment and personnel **.
Five, the difference between lightning protection grounding and electrical grounding:
1. Protective grounding refers to connecting a non-charged metal part of an electrical device to a grounding device under normal circumstances to prevent the part from being suddenly charged under a fault condition and causing harm to the human body.
2. Working grounding is to ground the neutral point of the transformer. Its main role is to stabilize the potential of the system, that is, to alleviate low-voltage systems due to one-phase grounding; lightning protection grounding and electrical grounding can be connected together. However, it is not possible to connect the lightning protection down conductor and the protective connection down conductor on the ground and connect it to the ground electrode, because the lightning current will be shunted to the equipment by the PE line at the same time when the lightning current passes through the lightning protection In the event, personnel will be struck by lightning.
3. Lightning protection ground and electrical ground can be connected together. However, it is not possible to connect the lightning protection down conductor and the protective connection down conductor on the ground and connect it to the ground electrode, because the lightning current will be shunted to the equipment by the PE line at the same time when the lightning current passes through the lightning protection In the event, personnel will be struck by lightning.
3. The down conductor of the PE line protective grounding should be connected to the ground electrode separately. The farther the distance between the down conductor of the PE line and the lightning protection down line is, the better it is. , Let the lightning current flow into the ground, it will not diffuse from the down conductor of the PE line to the equipment case.