Lightning protection design scheme should clearly state the design basis. Since the development history of lightning protection technology is not long, the lightning protection technology is not perfect, and the electromagnetic environment that needs to be dealt with is becoming more and more complex, the lightning protection technology is constantly improving, and the lightning protection technology standard is constantly revising. Therefore, the latest version of the cited standard should be mastered and used to ensure the advancement of the reference standard and the use of this standard. Generally, IEC standards should be encouraged based on current national and industrial standards. 
LED street lamps are exposed to the outdoors, and there is a danger of lightning. Therefore, as a design manufacturer, it is necessary to do a good job of lightning protection measures. In the following, we introduce several lightning protection strategies for LED street lamps. 
 
Lightning strike mainly has the following four types : 
 
 
 
1. Direct strikes 
 
Direct lightning contains great energy, peak voltage up to 5000 kv lightning into the ground, with great destructive power. It will have the following three impacts : 
 
( 1 ) Huge rich current flows down in a few microseconds, making the ground potential quickly pick up, resulting in counterattack accidents, endangering personal and equipment safety. 
 
( 2 ) Lightning current produces strong electromagnetic waves and induces extremely high pulse voltage on the power line and signal line. 
 
( 3 ) Lightning flows through electrical equipment generate extremely high heat, causing fire or explosion accidents. 
 
2. Conducted mines 
 
Distant lightning strikes the line or the extremely high voltage generated by electromagnetic induction, which is transmitted from outdoor power lines and communication lines to electrical equipment inside the building. 
 
3.Induction thunder
Frequent discharges between clouds produce strong electromagnetic waves that cause common mode and differential mode interference, affecting the operation of electrical equipment. 
 
4. Switching overvoltage 
 
The inductive and capacitive load in the power supply system can open or disconnect, the earth pole short circuit, the power line short circuit, etc., which can generate high voltage pulses on the power line. The pulse voltage can reach 3 to 5 times the normal voltage, which can seriously damage the equipment. The damage effect is similar to lightning strike. 
 
So how will we prevent lightning accidents ? The following ways are the most effective ways to prevent street lamps from being damaged by lightning, according to the research of Huaxing Power Supply Research Laboratory : 
 
1. Combination of external lightning protection and internal lightning protection 
 
At present, the general LED street lamps are all conductor materials outside, which is equivalent to a lightning rod itself. In the design, the lead-off line and the ground network must be installed. These systems constitute the external lightning protection system. The system can avoid LED street lamp fire and personal safety accidents caused by direct lightning. Internal lightning protection system refers to the protection of equipment by grounding and setting voltage protection inside the street lamp. The system can prevent induction lightning and other forms of overvoltage intrusion, causing power damage, which is not guaranteed by the external lightning protection system. The two complement each other. Internal lightning protection system in many devices, such as shell, access to protected areas of cable, metal pipelines, etc. are connected to the external lightning protection system or overvoltage protector, and equipotential connection. 
 
2. Lightning protection equipotential connection
In order to completely eliminate the devastating potential difference caused by lightning, power lines, signal lines, metal pipelines and so on should be equipotentially connected with overvoltage protectors. Local equipotential connection should also be carried out at the interface of each inner protection zone. Each local equipotential connection should be connected with each other, and finally connected with the main equipotential. 
 
3. Establishment of lightning protection zones 
 
At present, in addition to the power supply equipment, LED street lamps also set up some communication equipment to control the switch and brightness of street lamps. These equipment and power supply need to be placed in the lightning protection area, and the protection area is directly shielded by the shell. The electromagnetic field here is much weaker. 
 
4. High-quality protection equipment - lightning protection modules and overvoltage protection modules 
 
The function of lightning arrester is to connect the protected system into the equipotential system in the shortest time ( nanosecond level ), so that the equipotential of each port of the equipment is equal. At the same time, the huge pulse energy generated by lightning in the circuit is released to the earth through a short circuit, reducing the potential difference of each interface end of the equipment, so as to protect the equipment. 
 
LED street lamp power supply module should not only be designed according to the above requirements, but also must undergo strict inspection procedures : 
 
1. The control device with constant voltage output function or constant current output function or both functions should be tested by GB19510.12 / IEC61347 - 2 - 13.
2. For the control devices that only have the functions of controlling the logical changes of LED such as brightness, flicker and color, the GB19510.12 / IEC61347 - 2 - 11 safety standard test should be adopted. 
 
3. If a control device has both functions, it shall be inspected in accordance with GB19510.12 / IEC61347-2-13 safety standards. 
 
Practice has proved that scientific design and strict inspection can not only ensure that LED street lamp system is not damaged by lightning, but also eliminate the common mode and differential mode interference of lightning on power supply equipment.