1. Types of lightning

(1) Direct lightning strike. Direct lightning strike is also called direct lightning strike. The powerful lightning current of a direct lightning strike generates a large amount of heat energy in a flash through the object into the ground, which may cause the object to burn and cause a fire, as shown in Figure 1a. When lightning flows through the ground (or grounding body) flow into the surrounding soil, the formation of voltage drop around it, if someone stands near the place, will be due to step voltage and harm the human body.

(2) lightning induction. Lightning induction, also known as induction lightning, is divided into electrostatic induction and electromagnetic induction. Electrostatic induction is when there is a thundercloud over the metal roof of a building or other conductor, these conductors will induce a charge opposite to the polarity of the charge carried by the thundercloud. When the thundercloud discharge, the discharge channel in the charge quickly neutralize, but the charge gathered in the conductor is too late to immediately flow, the residual charge to form a high ground potential. This "static induction voltage" may cause a spark discharge, resulting in a fire or explosion, as shown in Figure 1b.

Electromagnetic induction is a lightning strike, lightning current in the surrounding space quickly formed a strong and changing magnetic field, in this electromagnetic field, the conductor will induce a larger electromotive force and induced current. If there is an opening in the conductor loop, it may cause spark discharge. If some of the conductors in the loop are in poor contact, local heating may occur. This is very dangerous for buildings that store flammable or explosive materials.

(3) lightning wave invasion. Lightning wave intrusion is also called high potential introduction. As overhead lines or metal pipelines are directly struck by lightning, or as a result of thundercloud discharge nearby, inductive lightning waves are generated on the conductors, and the impulse voltage is introduced into the building, accidents such as personal electric shock, equipment damage or fire may occur,

2. Lightning protection measures

For different buildings, according to the requirements of lightning protection, different measures are adopted to protect buildings from lightning or reduce the harm of lightning. In the electrical installation engineering, the lightning protection measures commonly used in buildings are as follows:

a. direct lightning strike B. lightning induction c. lightning wave invasion

(1) Measures to prevent direct lightning strikes. The main measure to prevent direct lightning strike is to try to guide the lightning current to drain into the earth according to the pre-arranged channel, so as to avoid the discharge of thundercloud to the protected building. Lightning, in fact, is lightning, lightning rod, lightning belt and lightning protection network as lightning arrester. The lightning protection device is composed of lightning receptor, down conductor and grounding device to prevent direct lightning strike.

The lightning receptor is the part directly used to receive lightning strikes, including lightning rods, lightning belts, lightning protection nets, and metal roofs and metal components used as lightning receptor. The down lead, also known as the current collector, leads the lightning current to the grounding device and is the metal conductor connecting the lightning receptor and the grounding device. The grounding device is a conductor that guides the lightning current to drain safely into the earth, and it is the general term of the grounding body and the grounding wire. The grounding body is a conductor buried in the soil or in the concrete foundation as a dispersion; the grounding wire is a connecting conductor from the connection of the down conductor to the grounding body.