LED Lighting: Analysis of Lightning Protection Design for LED Street Light Power Supply

There are four main types of lightning strikes:

1. Direct lightning

Direct lightning strikes contain enormous energy, and the peak current reaches 5000kV of lightning current into the ground, which has great destructive power. There are three effects that can be caused:

(1) The huge current is flowing down in a few microseconds, so that the ground potential is quickly picked up, causing a counterattack accident and endangering the safety of people and equipment.

(2) The lightning current generates a strong electromagnetic wave, which induces a very high pulse voltage on the power line and the signal line.

(3) Thunder current flows through electrical equipment to generate extremely high heat, causing fire or explosion accidents.

2. Conducted thunder

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

3. 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. Switch overvoltage

Inductive and capacitive loads in the power supply system can be opened or disconnected, 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 the CLP Huaxing Power Research Laboratory, the following methods are the most effective ways to prevent street lights from being damaged by lightning:

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 means that the interior of the street lamp is protected by 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.

2. Lightning protection equipotential bonding

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

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. 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 interfaces of the device is reduced, thereby protecting the device.

LED street light power modules must not only be designed in accordance with the above requirements, but must undergo a rigorous inspection procedure:

1. The 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.

2. For control devices that only have the function of controlling the brightness change of LED light, darkness, flashing, color, etc., GB19510.12/IEC61347-2-11 safety standard inspection shall be adopted.

3. If a control device has the functions of both, 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 can be eliminated.