Lightning protection design scheme and inspection standard for LED street light power supply against 4 types of lightning strikes

Lightning strike is a natural phenomenon, but it may cause great property loss and personal injury to human life. Therefore, in urban construction, relatively high and metal buildings and public facilities must consider the function of lightning protection. The common lightning strikes we see are mainly the following four types:

1. Direct lightning strike

Direct lightning contains huge energy, and the peak voltage can reach 5000kV. The lightning current entering the ground is extremely destructive. It will cause the following three effects:

(1) A huge amount of current flows to the ground within a few microseconds, causing the ground potential to rise rapidly, resulting in a counterattack accident and endangering the safety of people and equipment.

(2) Lightning current generates powerful electromagnetic waves, inducing extremely high pulse voltages on power lines and signal lines.

(3) Lightning current flowing through electrical equipment generates extremely high heat, causing fire or explosion accidents.

2. Conducted lightning

Extremely high voltages generated by distant lightning striking lines or by electromagnetic induction are transmitted through outdoor power lines and communication lines to electrical equipment inside buildings.

3. Induction Lightning

Frequent discharges between clouds generate strong electromagnetic waves that cause common-mode and differential-mode interference, affecting the operation of electrical equipment.

4. Switch overvoltage

The opening or disconnection of inductive and capacitive loads in the power supply system, ground short circuit, power line short circuit, etc. can all generate high-voltage pulses on the power supply line. The pulse voltage can reach 3 to 5 times the normal voltage, which can seriously damage the equipment. The destructive effect is similar to that of lightning strikes. So how can we prevent lightning strikes? The following methods are the most effective ways to prevent street lamps from being damaged by lightning:

1. Combination of external and internal lightning protection

At present, the exterior of general LED street lights is made of conductive materials, which is equivalent to a lightning rod. The design must be equipped with down conductors and ground grids. These systems constitute an external lightning protection system. This system can prevent LED street lights from causing fires and personal safety accidents due to direct lightning strikes. The internal lightning protection system refers to the protection of equipment inside the street light by grounding, setting voltage protection, etc. This system can prevent induced lightning and other forms of overvoltage from invading and causing power supply damage, which cannot be guaranteed by the external lightning protection system. The two are complementary and complement each other. The internal lightning protection system must be connected to the external lightning protection system or an overvoltage protector must be installed on many devices such as the outer casing, cables entering and leaving the protection area, and metal pipes, and make equipotential connections. 2. Lightning protection equipotential connection

In order to completely eliminate the destructive potential difference caused by lightning, power lines, signal lines, metal pipes, etc. must be connected to the same potential using overvoltage protectors. Local equipotential connections must also be made at the interfaces of each inner protection zone. Each local equipotential connection must be connected to each other and finally to the main equipotential connection.

3. Set up lightning protection areas

At present, in addition to power supply equipment, LED street lamps also have some communication equipment to control the switch and brightness of street lamps. These equipment and power supplies need to be placed in the lightning protection area, which is directly shielded by the shell. The electromagnetic field here is much weaker.

4. High-quality protection equipment - lightning protection module and overvoltage protection module

The function of the lightning arrester is to connect the protected system to the equipotential system in the shortest time (nanosecond level) to make the ports of the equipment equal in potential. At the same time, the huge pulse energy generated by lightning in the circuit is released to the ground through the short-circuit line, reducing the potential difference of each interface end of the equipment, thereby protecting the equipment.

LED street light power modules must not only be designed in accordance with the above requirements, but also must undergo strict inspection procedures.

1. Control devices with constant voltage output function, constant current output function or both functions should be inspected using the GB19510.12/IEC61347-2-13 safety standard.

2. For control devices that only have the function of controlling the brightness, flashing, color and other logical changes of LEDs, the GB19510.12/IEC61347-2-11 safety standard should be used for inspection.

3. If a control device has both of the above functions, it should be inspected in accordance with the GB19510.12/IEC61347-2-13 safety standard.

Practice has proved that scientific design and strict testing can not only ensure that the LED street light system is not damaged by lightning, but also eliminate the common mode and differential mode interference of lightning on the power supply equipment.