The harm of lightning is evident to all. However, in recent years, with the renovation of the power grid, especially the renovation of urban power grids and the construction of substation automation systems, people may still have insufficient understanding of lightning protection and grounding protection for these devices, resulting in multiple lightning accidents, paralysis of automation systems, and some power grid equipment accidents, causing serious losses. Therefore, it is necessary for the editor of graphite grounding to explore the lightning protection and grounding issues of power supply and distribution systems, in order to provide some assistance for design and construction personnel.

Lightning protection and grounding of power lines

Lightning protection and grounding of transmission lines

The lightning protection of transmission lines should be based on the voltage level, load nature, and system operation mode of the line, combined with the strength of lightning activity, terrain characteristics, and soil resistivity in the local area. Through technical and economic comparisons, reasonable lightning protection methods should be adopted.

It is not advisable to install lightning protection wires along the entire 5kV line. Generally, lightning protection wires of~km should be installed on the incoming section of the substation. At the same time, lightning protection wires should be installed in areas with strong lightning activity, or metal oxide lightning arresters should be installed on the line.

The 0kV line should be equipped with lightning protection wires along the entire line, and double lightning protection wires should be used in mountainous areas; However, in areas where the average number of thunderstorm days per year does not exceed 5 days or where operational experience proves that lightning activity is mild, lightning protection lines may not be installed.

The 0kV line should be equipped with lightning protection wires along the entire line, and double lightning protection wires should be used.

For the installation of lightning protection wires on the transmission line, attention should be paid to the protection angle of the lightning protection wire on the tower to the side conductor, generally using a protection angle of 0 ° to 0 °, and the grounding of the tower should be done well. According to the different soil resistivity, the power frequency grounding resistance of the tower should not exceed the values listed in the table.

Grounding resistance of the tower

Soil resistivity (Ω· m) 00 and below 00 to 500, 500 to 000

Power frequency grounding resistance (Ω) 050

For the technical parameters of metal oxide surge arresters installed on 5kV power lines, the following conditions should generally be met:

① The continuous operating voltage (effective value) shall not be less than 408kV;

② The rated voltage (effective value) shall not be less than 5kV;

③ The DC mA reference voltage shall not be less than 7kV (within the range of 7-74kV);

④ The residual voltage (peak value) under the standard discharge current of 5kA level shall not exceed:

Lightning impulse 4kV, operational impulse 4kV, steep wave impulse 54kV.

⑤ 000 μ s square wave current (peak) 00A.

⑥ The insulation configuration shall be determined according to the requirements of the line pollution level.

Lightning protection and grounding of distribution lines

Like transmission lines, lightning protection for distribution lines can also use lightning rods or surge arresters, and the measures taken for different voltage levels and different lines are also different.

0kV bare wire circuit. For 0kV bare wire lines, lightning rods can be used for lightning protection in principle. However, due to high costs and inconvenient construction, lightning rods are generally not used. Instead, lightning arresters are installed in some sections with frequent lightning activity, and tower grounding is done according to requirements.

0kV insulated wire line. Due to the urban network renovation in recent years, most urban lines in Beijing have been replaced with cross-linked polyethylene overhead insulated lines, but their lightning protection measures have not changed from those of the original bare wire lines, resulting in dozens of lightning insulation line breakage accidents. For overhead insulated lines, the following lightning protection measures can be taken: ① Installing lightning protection wires, which have the best lightning protection effect, but are feasible, difficult, and costly. ② Improving the voltage resistance level of line insulators and replacing 0kV insulators with lightning protection insulators will greatly enhance the lightning protection level. ③ Install lightning arresters in multiple minefields or at certain intervals to reduce lightning strikes and wire breakage accidents. ④ Extending the flashing path can easily extinguish the arc, locally increasing insulation strength, such as strengthening insulation at the connection between the wire and the insulator, and using long flashing path lightning arresters. ⑤ Partially stripping the insulated wire, making it partially bare wire, so that the arc can slide on the stripped part instead of being fixed at a certain point for erosion, and also providing a grounding point for future construction.

Low voltage distribution lines. Low voltage lines should be equipped with low-voltage lightning arresters or breakdown fuses at the transformer outlet, and grounding devices should be properly grounded. The grounding resistance of the grounding device should not exceed 4 Ω. The neutral line in a low-voltage power grid with a neutral point directly grounded should be grounded at the power supply point. Low voltage distribution lines should be repeatedly grounded at the terminals of the main and branch lines. The grounding resistance of the repeated grounding device should not exceed 0 Ω per year. For longer lines, the repeated grounding should not be less than. Especially to prevent lightning waves from invading users along low-voltage distribution lines, the iron corners of insulators on the grounding line should be grounded with a grounding resistance of less than 0 Ω. This is particularly important for our one household one meter renovation work. The above is the introduction of graphite grounding by the editor.