1、 The principle of lightning generation

The Earth we inhabit is a planet with5When a sphere with a negative charge of ten thousand coulombs is approached by clouds with different charges in the sky, or when clouds have different polarities of charges from the ground and are close enough, breakdown discharge occurs. Accompanied by the thunderous roar and lightning tearing through the sky, the magnificent scenery of nature is repeated time and time again---Thunder and lightning occurred.

2、 The harmfulness of lightning

Lightning strikes cause enormous damage to people, equipment, and buildings through their instantaneous eruption of electric, electromagnetic, chemical, and mechanical effects. According to rough statistics, the number of people who die from lightning damage worldwide every year3000More than one person, with direct property losses exceeding10USD100mn The development of modern information technology and the high integration of electronic technology have brought infinite prospects to human civilization. However, the high potential intrusion of induced lightning poses a huge threat to electronic devices. This poses a new challenge for lightning protection technology.

However, just like all things have two sides, lightning also plays an irreplaceable and significant role:

Thunder gave birth to life on Earth, and many biological hypotheses about the origin of life are related to lightning. It also created the civilization history of human use of fire, and due to the phenomenon of lightning triggering fires, humans bid farewell to the barbaric life of eating and drinking blood;

3、 The way of lightning invasion

Lightning intrusion is generally divided into two types: direct lightning and induced lightning:

Direct lightning strikes refer to the discharge phenomenon caused by charged cloud clusters directly hitting the ground and impacting objects in that area; Direct lightning strikes are generally based on the principle of discharge at the tip, so they generally harm tall structures.

Inductive lightning is generally based on electromagnetic induction and circuit principles, so its range of harm is wide, the probability is high, and it is almost ubiquitous, making it difficult to prevent. Inductive lightning can propagate along the electromagnetic field in space. Without a reasonable metal shielding net, lightning electromagnetic pulses are almost ubiquitous. Inductive lightning can propagate along metal water pipes, gas pipes, and metal structures entering buildings, as well as along the power supply entering buildingslineTransmission of telephone lines, video RF cables, computer network metal wires, and various control signal metal cables.

In addition, the down conductor and the steel mesh inside the building serving as the down conductor are also pathways for the propagation of induced lightning.

4、 Protective measures against lightning

Methods for preventing direct lightning strikes (also known as external lightning protection)

200Years ago, American scientist Franklin invented the lightning rod through long-term research. It uses the principle of pointed discharge to find a safety barrier for humans to protect against direct lightning strikes. The main structures of modern direct lightning strike facilities are: lightning arrester, down conductor, and grounding grid.

Methods for preventing induced lightning (also known as internal lightning protection)

1Shielding: divided into building large shielding Faraday cage and small inter cell shielding---Metal mesh shielding and metal material shielding;

The cable is buried in a metal tube for shielding, and both ends are grounded, which can reduce the surge current to30%.

2Diversion: The power supply line is equipped with lightning arresters of no less than three levels for graded discharge; Install signal lightning arresters at the entrances of each signal line (metal).

3Grounding: All lightning arresters are grounded at the bottom.

4Ground potential counterattack-Overlapping;

When a direct lightning strike enters the ground through lightning protection facilities and discharges, the potential at the entry point will sharply increase. If this high potential is introduced, it will cause harm to equipment and personnel due to the high potential difference, which is called ground potential counterattack. The countermeasure taken to prevent the harm of ground potential counterattack is equipotential connection. Connect an equipotential copper busbar to the grounding grid indoors, and connect the metal frame, electrical equipment metal casing, lightning arrester grounding terminal, metal pipe, and trough casing to the equipotential copper busbar.

5Conduction: Install lightning rods, lightning strips, and wires to guide lightning down to the ground;

6Other lightning protection methods: avoidance

By adjusting time and space, avoid lightning strikes: for example, reasonable selection of terrain and landforms, and disabling equipment during lightning strikes.

7Lightning suppression: using rockets, lightning arresters, etc. to eliminate the generation of lightning;

In summary, modern lightning protection technology measures can be summarized as avoidance, equipotential bonding, conduction, diversion, grounding, and shielding.