Safety knowledge of lightning protection.

# Education # Introduction Lightning can be generally divided into three categories: hot lightning, front lightning (hot front lightning and cold front lightning) and terrain lightning. In our daily life, we should know how to prevent lightning strikes and avoid injuries. The following is to sort out the relevant content for everyone.

Lightning protection safety knowledge

I. Lightning

1. Electrification of Thunderstorm Cloud

The formation process of positive and negative charge regions with different polarities in thunderstorm clouds is called the charging process of thunderstorm clouds. Thunderstorm clouds contain strong updraft and water particles with different scales and phases. Through the diffusion, ion capture, collision and separation between particles, particles of different scales are charged with different polarities, which are separated under the action of airflow and gravity to form charge regions with different polarities. When the local electric field in the thunderstorm cloud exceeds about 400kV/m, lightning can be generated.

2. Classification of lightning

(1) cloud flash.

Usually, more than half of the lightning discharge process occurs between the main positive and negative charge regions in thunderstorm clouds, which is called intracloud discharge process. The lightning in the cloud, together with the lightning between clouds and cloud-gas discharge with relatively low probability, is called cloud flash.

(2) lightning. Another kind of lightning is the discharge between clouds and the ground, which is called lightning. A complete lightning strike is defined as "lightning" with a duration from several hundred milliseconds to 1 second. A lightning stroke includes one or several large current pulse processes, which are called "lightning stroke", and the rapidly changing part is called "return stroke". The interval between flashes is generally tens of milliseconds. Lightning discharge can radiate broadband electromagnetic waves, from several hertz to several hundred GHz.

3. Several forms of lightning strike

First, direct lightning strike

Lightning strikes buildings, other objects, the earth or lightning protection devices directly, resulting in electrical effect, thermal effect and mechanical force.

B, induced lightning strike

When lightning discharges, electrostatic induction and electromagnetic induction are generated on nearby conductors, which may cause sparks between metal parts.

C, lightning wave invasion

Due to the action of lightning on overhead lines or metal pipelines, lightning waves may invade houses along these pipelines, endangering personal safety or damaging equipment.

D, lightning electromagnetic pulse

It is the electromagnetic field effect produced by lightning current and lightning electromagnetic field as interference sources. Refers to the effect of lightning directly hitting buildings and lightning protection devices nearby. Most of them are interfered by connecting conductors, such as lightning current or partial lightning current, potential rise of lightning struck equipment, coupled conduction of electromagnetic radiation, etc.

4. General selectivity of lightning strike

(1) Lightning strikes mostly occur in areas with metal deposits, rivers and lakes, and underground water outlets. The land on the hillside adjacent to the paddy field and the boundary part of the soil with different resistivity are vulnerable to lightning strike.

(2) It is also vulnerable to lightning strikes in lakes, swamps, diwa areas and places with high groundwater level. In addition, the condition of ground facilities is also an important factor affecting lightning strike selectivity.

(3) High-rise buildings and structures are vulnerable to lightning strikes. Buildings with metal structures, factories with a large number of metal bodies inside, or rooms that are often wet inside are vulnerable to lightning strikes because of their good conductivity.

(4) In the wilderness, even if the building is not high, it is relatively isolated and prominent, and it is more vulnerable to lightning strikes; Such as rest pavilions, grass sheds, water car sheds, tool sheds, etc.

(5) The hot air discharged from the chimney and a large number of air masses containing conductive particles and free molecules discharged from the chimney are more conductive than air, which is equivalent to heightening the chimney and easily causing lightning strikes.

5. Basic situation of lightning activity in Hainan.

Hainan is the hardest hit area with the highest lightning incidence rate in China, with an average annual thunderstorm day of 1 13 days, reaching 149 days. The average number of thunderstorm days in Danzhou is 1 18.3 days, reaching 139 days.

The annual average lightning density in Hainan is 1 1.53 times /Km2, which is the highest in China. The lightning density is higher in the east, north, west and middle of Hainan Island, but slightly lower in the southwest, south and southeast.

There is lightning from January to December every year. The concentration period is April-10.

Every year, lightning accidents cause 50-60 casualties and economic losses of nearly 100 million yuan.

Second, the destructive effect of lightning.

1 the destruction of lightning current shock wave

The temperature of lightning tunnel is as high as thousands to tens of thousands of degrees, and the air expands rapidly when heated, and spreads around at the speed of ultrasonic waves, producing powerful shock waves, which cause damage and injury to nearby buildings, people and livestock.

2. Destruction of electrodynamics effect of lightning current.

When lightning current passes through a conductor, a strong electromagnetic field will be generated in the space around it, and the current-carrying conductor in the magnetic field will be affected by the electric field, generating a strong electrodynamic force, which will break all kinds of wires or pipelines.

3. The electric effect of lightning damage.

The lightning discharge current can be as high as tens of KA to hundreds of KA, the voltage can be as high as hundreds of thousands of volts to millions of volts, and the lightning discharge power can reach more than 109- 10 12W. The lightning pulse current can generate a strong magnetic field as high as 1- 103 gauss (GS). Therefore, it is extremely destructive to all electrical equipment of human beings.

4. Destruction of thermoelectric effect of lightning current.

Strong lightning current will generate heat when it passes through the struck object. Because the lightning current is very large, the passing time is very short. If lightning strikes trees, buildings and structures, the struck object will generate a lot of heat in an instant, which will turn a lot of water inside the object into steam and expand rapidly, resulting in huge explosive force and damage. The temperature of lightning channel is as high as 6000℃- 10000℃, or even higher.

Third, the way of lightning damage.

1, direct lightning hazard: the hazard caused by lightning directly hitting ground objects. It can produce electric effect, thermal effect and electrodynamic effect, with great energy and destructiveness. Its incidence rate accounts for about 10- 15% of the whole lightning accident.

2. Hazard of induced lightning: When lightning strikes, electrostatic induction and electromagnetic induction will be generated on nearby objects, which may cause spark discharge between metal parts.

(1) Electrostatic induction of lightning;

When there is a thunderstorm cloud, the ground and buildings under the thunderstorm cloud will carry the same opposite charge as the lower end of the thunderstorm cloud under the action of the electric field of the thunderstorm cloud. When Lei Yun discharges, the charges on the thunderstorm cloud and the ground opposite charges quickly neutralize, and the Lei Yun electric field disappears. However, some objects on the ground, such as overhead lines, metal pipes, buildings, structures, etc., have a large resistance to the ground, and the heterogeneous charges generated by electrostatic induction can not be discharged in time, which can produce a high electrostatic induction voltage and may cause ground discharge.

(2) Lightning electromagnetic induction: Because lightning current is pulse current, under its impact, the surrounding space generates transient strong electromagnetic field, which induces high voltage on nearby conductors, and lightning electromagnetic induction is extremely harmful to weak current equipment (when B > 0.03GS can cause misoperation of microelectronic equipment, b >；; 0.75GS can cause false injury, b > 2.4GS will cause permanent damage).

3. Invasion hazard of lightning wave: Due to the effect of lightning on overhead lines or metal pipelines, lightning waves invade the room along these pipelines, endangering personal safety or damaging equipment.

4. The harm of lightning high-voltage counterattack: in objects (metal bodies, trees, buildings, etc. ) struck by direct lightning, or struck by lightning protection devices (lightning receptor, down conductor, grounding body and surge protector), at the moment of lightning strike, there is a high potential difference (voltage) between lightning and the earth, and the phenomenon that this voltage hits a metal object connected with the earth is counterattack (microelectronic equipment is damaged by lightning strike, 60%).

5. Spherical lightning: lightning discharge fireball or electrostatic high-voltage fireball.

6. The main causes of electrical fire and equipment damage caused by lightning strike are:

(1), lightning current and overvoltage introduced by each high-voltage power supply line into the information system power supply.

(2) The induced overvoltage caused by lightning induction damages the power supply and information system lines.

(3) Lightning discharge, overvoltage or overcurrent introduced along various metal pipes when lightning strikes buildings or nearby areas; At the same time, the lightning electromagnetic pulse generated by lightning discharge, due to the transient overvoltage or strong magnetic field radiation caused by space electromagnetic induction, leads to the damage of the information system in the building.

(4) Improper handling of grounding system technology of various electrical and information equipment causes potential difference and high voltage counterattack of grounding system of various equipment.

(5), lead to electrical equipment and line insulation damage, resulting in short circuit fault or leakage trip.

Lightning strikes can damage information systems, from system collapse or misoperation to permanent damage or personal injury to system hardware.

Four. Lightning strike and personal safety

(A) several forms of lightning attacks on the human body

1, direct lightning strike

2. Contact with lightning

3. Side flashover

4. Jump voltage

(2) Basic measures for personal safety protection

(a) near the thunderstorm weather conditions, when you are in a building with good direct lightning protection facilities, you should pay attention to the following four points:

1, can't stay on the roof (surface) of the building.

2. Pay attention to close the doors and windows.

It is not advisable to use shower.

4, should not be close to the building * exposed metal objects, such as water pipes, heating gas pipes, and do not use electrical equipment.

(2) When approaching thunderstorm weather, when working outdoors (in the field), six points should be noted:

1, which is not suitable for entering shelters such as shacks, huts, wooden houses and sentry boxes without lightning protection facilities.

2. It is not advisable to shelter from the rain and carry metal objects and tools under the big tree.

3. It is not advisable to play umbrellas and wooden (bamboo) poles in the wild.

4. Not suitable for operations and activities on the water surface or at the junction of land and water.

It is not advisable to drive a motorcycle or ride a bike.

6. Outdoor ball games (football, basketball, golf, etc.). ) are not suitable.

(three) near the thunderstorm weather, it is not appropriate to stay in the following places.

1, hilltops and slopes;

2. Mining areas, various parking lots and sports fields;

3. Swimming pools, lakes, rivers and beaches;

4. Iron railings, metal clotheslines, overhead lines and rails;

5. When lightning strikes, if you are isolated in the exposed area and feel your hair stand up, you should immediately bend your knees forward and squat down with your hands clenched.

(four) when lightning strikes, you should look for the following places to cover.

1. Buildings protected by lightning protection measures.

2. Buildings with large metal frames.

3, large buildings without lightning protection measures.

4. All kinds of vehicles with metal roofs and ships with metal shells.

(3) Lightning protection safety measures at the construction site

1, the construction site should have a safe place to avoid lightning; The metal shell of each electrical equipment should be grounded, and the power cord should be equipped with SPD protection;

2. When installing metal pipes or laying power and signal cables outdoors, one end should be grounded first, and operation should be stopped when thunderstorm weather approaches;

2, near the thunderstorm weather, stop using all kinds of electrical equipment, such as welding machine, cutting machine, and stay away from these equipment and cables, don't carry metal tools;

1. In case of thunderstorm, teachers and students should be active in urban areas, close doors and windows, do not swim in open water or engage in other water activities, and stay in open areas such as playgrounds is strictly prohibited.

2. Don't open an umbrella in the wild, don't carry metal appliances or articles on your shoulders, don't use or try to avoid communication facilities such as mobile phones and telephones, and don't stay near iron fences, metal clotheslines and overhead metal bodies. And don't stand near roofs, high walls, telephone poles or antennas.

3. It is not advisable to drive a motorcycle or ride a bicycle, and it is forbidden to walk along the rails.

4. Avoid the nearest building quickly. When there is nowhere to hide in the wild, find a low-lying place to hide. Never hide under a big tree, near wires and communication cables, or enter temporary shacks and sentry boxes without lightning protection facilities.

5. Do not touch indoor and outdoor grounding wires, power cables, communication cables and other metal conductors entering and leaving the room.

6. In strong thunderstorm weather, the power supply and incoming communication cable of special equipment classroom should be cut off, and teachers and students should stay away from outdoor satellite receiving antennas.