April to September every year is the frequent season of lightning disasters in South China, which brings people life safety and property losses. This paper introduces the causes of lightning, its harm to construction machinery, and the prevention methods and techniques of lightning disaster. These methods and techniques have universal reference significance for colleagues to prevent lightning disasters in the construction process. Keywords: prevention of mechanical hazards caused by lightning 1 Lightning is a common discharge phenomenon in nature. There are many theories to explain the generation of lightning. Generally speaking, we think that the hot air in the atmosphere rises and rubs against the cold air at high altitude, thus forming small water droplets with positive and negative charges. When the positive and negative charges accumulate to a certain value, strong electric fields will be formed between clouds with different polarities and between clouds and the ground, resulting in cloud-to-cloud and cloud-to-ground discharge processes, commonly known as lightning. Specifically, the friction of ice crystals, the breaking of raindrops, the freezing of raindrops and the collision of clouds can make cloud particles charged. Generally, clouds are positively charged at the top and negatively charged at the bottom. Two kinds of charges with different polarities will form a strong electric field inside the cloud or between the cloud and the ground, and a strong electric spark will erupt instantly, which is what we see as lightning. In the lightning channel, the current is extremely strong, the temperature can suddenly rise to 20000 degrees Celsius, the air pressure suddenly increases, and the air expands violently, so people will hear explosive sound wave oscillation, which is thunder. 2 types of lightning hazards there are three main types of lightning hazards: the first is direct lightning. Refers to the strong discharge of Lei Yun at a certain point on the earth. Can directly hit the equipment, lightning can hit overhead lines, such as power lines, telephone lines. Lightning current enters the equipment along the wire, causing damage. The second is induced lightning. It can be divided into electrostatic induction and electromagnetic induction. When charged Lei Yun (generally negatively charged) appears on the wire, a large number of opposite charges are bound on the wire due to electrostatic induction. Once Lei Yun releases a target, the negative charge on Lei Yun disappears immediately. At this time, a large number of positive charges on the conductor still exist and enter the ground along the conductor in the form of lightning waves, causing equipment damage. When lightning current flows into the earth along the conductor, due to its high frequency and strength, a strong alternating electromagnetic field is generated near the conductor. If the equipment is in this situation, it will induce high voltage and cause damage. Pay special attention to sensitive electronic equipment. The third is the increase of ground potential. When the lightning current of 10kA is grounded through the lower conductor, we assume that the grounding resistance is10Ω. According to Ohm's law, we know that the voltage at ground point A is 100kV. Because point A is connected with point B, point C and point D, the voltage of these points is 100kV. And point e is grounded, and its voltage value is 0. There is a voltage difference of 100kV between point D and point E of the equipment, which is enough to damage the equipment. According to relevant statistics, the harm caused by direct lightning only accounts for 15%, and the harm caused by induced lightning and rising ground potential accounts for 85%. At present, the disasters caused by direct lightning have been obviously reduced, but with the development of urban economy, the harm caused by induction lightning and lightning wave intrusion has greatly increased. Generally, lightning rods on buildings can only prevent direct lightning, but the induced lightning and pulse voltage generated by powerful electromagnetic fields can sneak into the room, endangering weak current equipment such as televisions, telephones and networked microcomputers. 3 Lightning protection methods and technologies With the development of science and technology, although it is impossible for human beings to completely control violent lightning, after long-term exploration and practice, they have accumulated a lot of lightning protection knowledge and experience and formed a series of effective lightning protection methods and technologies. (1) Lightning connection is to let the lightning energy in a certain range be discharged into the earth according to the channels designed by people. Capture the lightning discharge within a certain protection range and incorporate it into the pre-designed reasonable way to discharge to the ground. Lightning rod is a device that actively receives lightning, and its function is to lead lightning current into the earth. Lightning rod and lightning belt are developed on the basis of lightning rod. Using lightning rod is the most important and basic lightning protection measure. (2) Grounding means that the lightning energy that has been incorporated into the lightning protection system is discharged into the earth. Good grounding can effectively reduce the voltage on the down conductor and avoid counterattack. In the past, some specifications required electronic equipment to be grounded separately in order to prevent stray current or transient current in the power grid from interfering with the normal work of the equipment. Grounding is the most basic link in lightning protection system. If the grounding is not good, the lightning protection effect of all lightning protection measures can not be exerted. Lightning protection and grounding is the most basic safety requirement in the Code for Installation and Acceptance of Lightning Protection Facilities. (3) When the lightning arrester catches the lightning, the down conductor immediately rises to a high potential, which will cause side flashover to the conductors around the lightning protection system that is still at ground potential, and make its potential rise, thus causing harm to personnel and equipment. In order to reduce the risk of flashover, the simplest method is to use the equalizing ring to connect the conductor at ground potential to the grounding device. If the distance between metal facilities, electrical devices and electronic equipment and the conductor of lightning protection system, especially the lightning arrester, cannot meet the specified safety requirements, thick wires should be used for equipotential connection with lightning protection system. In this way, when lightning passes, all facilities immediately form an "equipotential island" to ensure that there is no harmful potential difference between conductive parts and no lateral flashover discharge. Perfect equipotential bonding can also prevent the lightning current from entering the ground and causing the counterattack caused by the rise of ground potential. (4) Shunt shunt is to connect a suitable lightning arrester in parallel between all the wires led out outdoors and the ground wire. When the overvoltage wave generated by direct lightning or induced lightning on the line enters the room or equipment along these wires, the resistance of the arrester suddenly drops to a low value, which is close to the short circuit state, and the lightning current is divided into the earth. Shunting is the focus of the rapid development of modern lightning protection technology, and it is also the key measure to protect all kinds of electrical and electronic equipment. Because a small part of lightning current will still enter the equipment along the conductor after shunt, it is still very dangerous for microelectronic equipment that is not resistant to high voltage, so before the conductor enters the bushing, it is necessary to shunt this kind of equipment in multiple stages. When shunt lightning protection measures are adopted, special attention should be paid to the selection of lightning arrester performance parameters, because the installation of additional facilities will affect the performance of the system more or less. (5) Shielding is to surround the protected object with metal mesh, foil, shell, tube and other conductors to block the passage of lightning pulse electromagnetic field invading from space. Shielding is the most effective method to prevent the influence of lightning electromagnetic pulse radiation on electronic equipment. 4 the harm of lightning to construction machinery and its prevention. Highway construction work is carried out in the open air. The electrical control system of construction machinery, especially the microelectronic control device, is likely to be damaged by lightning direct strike or lightning induced overvoltage. Qingyuan section of Beijing-Zhuhai Expressway is located in limestone mountain area, which is a high incidence area of lightning strikes in thunderstorm season. Whenever the sky is overcast and it rains heavily, lightning often attacks construction machinery head on. Sometimes, even if there is no rain cloud or rain in the sky, induced lightning will happen from time to time, and the surge voltage generated by it will invade and damage the micro-electric control device of the pavement paver. Therefore, lightning protection is imperative. (1) Installation of lightning rod device in asphalt mixture mixing plant Because asphalt mixture mixing equipment and its supporting machinery share a production workshop, centralized lightning protection is easier. Therefore, lightning rods are installed in the mixing station. The height of the lightning rod is higher than the highest point of the mixing building, so as to achieve an effective protection radius and prevent lightning from directly hitting any working machine. Lightning rod grounding should be reliable. Because the geological soil in limestone mountain area is dry and hard, and the soil resistance value is too large, the grounding grid embedding method is different from that in Guangzhou-Zhuhai East Line. It is required to bury the pit at the point of angle steel pile of grounding grid, with a depth of about 1.0m, and the angle steel should be exposed out of the pit for about 20cm. The pit should be filled with charcoal and granular raw salt as drag reduction media in proportion, and the weight ratio of raw salt to charcoal is 1: 10, that is, 1kg raw salt is mixed with 10kg charcoal, and then filled and covered. This can ensure that the grounding resistance value is below 4. When lightning strikes, the lightning rod and its leads quickly introduce powerful lightning current into the earth through the grounding grid to prevent lightning from directly hitting the electromechanical system. In addition, the asphalt mixture mixing operation control room connects the working grounding and protective grounding of microelectronic control system in the operation room with the control room shell of metal structure through conductors, and then leads it into the underground grounding network through grounding wires to keep it equipotential to prevent static electricity and lightning. (2) Installation of Overvoltage Protector for Electrical Control Device of Pavement Paver Machinery Because the pavement paver machinery moves at any time, lightning protection cannot be concentrated. The electrical control device of mobile machinery is most vulnerable to the intrusion of lightning surge voltage in open air, such as the pressure sensor for asphalt paver to control pavement smoothness and mechanical positioning. In order to protect these mechanical microelectronic control devices with high control sensitivity from the invasion and destruction of induced lightning surge voltage, overvoltage protectors are installed according to the different structural characteristics of each mechanical control device. Conclusion The damage of lightning to electromechanical control devices, especially microelectronic devices, is a common natural disaster. In order to avoid lightning damage, different lightning protection methods should be adopted according to the different structural characteristics of electromechanical control devices. As long as the lightning protection equipment is reasonably selected, professional lightning protection companies should regularly test the lightning protection facilities to assess whether the lightning protection facilities meet the requirements of national standards. Construction projects shall set up a person responsible for lightning disaster prevention, be responsible for lightning protection safety, establish various lightning protection safety work systems, and establish a system for regular inspection of lightning protection facilities, inspection after thunderstorms and daily maintenance. In the design and construction of lightning protection facilities, the construction unit shall comprehensively consider factors such as geology, soil, meteorology, environment, characteristics of protected objects, laws of lightning activity, and adopt safe, reliable, technologically advanced and economical design and construction. It will greatly reduce the losses caused by lightning disasters.