LED street light power supply several tricks lightning protection strategy

- Nov 07, 2019-

Street lights are installed outdoors, and lightning strikes are a very big threat. Lightly, the street lamp is damaged, and in the worst case, it causes fire or casualties and causes huge losses. Here, I will tell you about the impact of lightning on LED street lights and preventive measures.

This article concludes that there are four main types of lightning strikes:

Direct lightning

The direct lightning strike contains enormous energy, and the lightning current with a peak voltage of up to 5000kV enters the ground and has great destructive power. There are three effects that can be caused:

a Huge current is flowing down in a few microseconds, causing the ground potential to rise quickly, causing counterattacks and endangering personal and equipment safety.

b Lightning current generates powerful electromagnetic waves that induce extremely high pulse voltages on the power and signal lines.

c Lightning current flows through electrical equipment to generate extremely high heat, causing fire or explosion.

Conductive thunder

The lightning strikes in the distance or the extremely high voltage generated by the electromagnetic induction are transmitted from the outdoor power supply line and the communication line to the electrical equipment in the interior of the building.

Inductive thunder

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

4. Switching overvoltage

Inductive and capacitive loads in the power supply system can be turned on or off, short-circuited to the ground, short-circuited in the power supply line, etc., and high-voltage pulses can be generated on the power line. The pulse voltage can reach 3 to 5 times of the normal voltage, which can seriously damage the equipment. . The damage effect is similar to lightning strikes.

So how do we prevent lightning strikes? After research by CLP Huaxing Power Research Laboratory, the following ways are the most effective ways to prevent street lights from being damaged by lightning:

4.1 External lightning protection combined with internal lightning protection

Nowadays, the general LED street lamp is made of conductor material, which is equivalent to a lightning rod. It is necessary to install the down conductor and the ground net. These systems constitute an external lightning protection system. The system can avoid fire and personal safety accidents caused by direct lightning strikes on LED street lights. The internal lightning protection system refers to the protection of the equipment inside the street lamp through grounding and voltage protection. The system prevents inductive lightning and other forms of overvoltage intrusion, resulting in power supply damage, which is not guaranteed by external lightning protection systems. The two are complementary and complement each other. The internal lightning protection system is connected to an external lightning protection system or an overvoltage protector and equipotential bonding on many devices such as the outer casing, cables entering and leaving the protection zone, and metal pipes.

4.2 lightning protection equipotential bonding

Thoroughly eliminate the destructive potential difference caused by lightning, power lines, signal lines, metal pipes, etc. must be equipotentially connected with an overvoltage protector, and local equipotential bonding is also required at the interface of each inner protective zone. The equipotential bonding should be connected to each other and finally connected to the main equipotential.

    4.3 Setting up lightning protection zones

At present, in addition to the power supply equipment, LED street lights will also be equipped with some communication devices for controlling the switch and brightness of the street lights. These devices and power supplies need to be placed in the lightning protection zone, and the protection area is directly shielded by the outer casing. The electromagnetic field here is much weaker.

4.4 High quality protection equipment - lightning protection module and overvoltage protection module

The role of the lightning arrester is to connect the protected system to the equipotential system in the shortest time (nanoseconds), so that the ports of the device are equipotential. At the same time, the huge pulse energy generated by the lightning strike in the circuit is released to the earth through the short-circuit line, and the potential difference between the interface ends of the device is reduced, thereby protecting the device. The CLP Huaxing Technology R&D team believes that LED street light power modules must not only be designed in accordance with the above requirements, but must undergo rigorous inspection procedures.

a Control device with constant voltage output function or constant current output function or both functions shall be tested by GB19510.12/IEC61347-2-13 safety standard.

b For control devices that only have the function of controlling the brightness of the LED, such as light and dark, flashing, color, etc., the GB19510.12/IEC61347-2-11 safety standard shall be used for inspection.

c If a control device has both functions, it shall be inspected in accordance with the safety standards of GB19510.12/IEC61347-2-13.

Practice has proved that after scientific design and strict inspection, not only can the LED street lamp system be protected from lightning damage, but also the common mode and differential mode interference of lightning on the power supply equipment. Let us introduce the power circuit design of lightning protection.

    5 lightning protection circuit design

    LED street lights are installed outdoors and are easily damaged by lightning strikes or surge voltages, so lightning protection units need to be designed. The lightning protection of the street lamp is divided into two levels. The first stage is to protect the direct lightning strike, and the metal lamp pole is grounded for processing. The second stage is to protect the conducted lightning and inductive lightning strikes, grid voltage fluctuations, etc., using the surge absorber Varistor as the main component to design the lightning protection unit.