LED lighting: lightning protection design guide for LED street light power supply

LED street lights are exposed to the outdoor, there will be the risk of lightning strikes, so as a designer must take measures to prevent lightning. Below we introduce several strategies for lightning protection of LED street lights.

There are four main types of lightning strikes:

1. Direct thunder

Direct lightning strikes contain great energy. The lightning current with a peak voltage of up to 5000kv enters the ground and is extremely destructive. Will cause the following three effects:

(1) The huge rich current flows down to the ground within a few microseconds, which makes the ground potential quickly pick up, causing a counterattack accident and endangering personal and equipment safety.

(2) The lightning current generates powerful electromagnetic waves and induces 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 Thunder

Lightning strikes in the distance or extremely high voltage caused by electromagnetic induction is transmitted from the outdoor power supply line and communication line to the indoor electrical equipment in the building.

3. Induction mine

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 turned on or off, ground short circuit, power line short circuit, etc., can generate high-voltage pulses on the power line, the pulse voltage can reach 3 to 5 times the normal voltage, can seriously damage the equipment . The destruction effect is similar to lightning strike.

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

1. The combination of external lightning protection and internal lightning protection

Nowadays, the exterior of general LED street lamps is made of conductive material, which is equivalent to a lightning rod. The design must be installed with a down conductor and a ground network. These systems constitute an external lightning protection system. The system can avoid fire and personal safety accidents caused by direct lightning strikes of LED street lamps. The internal lightning protection system refers to the protection of the equipment inside the street lamp by means of grounding and voltage protection. This system can prevent the induction of lightning and other forms of overvoltage intrusion, resulting in damage to the power supply, which is not guaranteed by the external lightning protection system. The two are complementary and complement each other. The internal lightning protection system must be connected to an external lightning protection system or an overvoltage protector on many devices, such as the casing, cables entering and leaving the protection zone, and metal pipes, and be connected with equipotential.

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 with overvoltage protectors, and local equipotential connections must also be made at the interface of each inner protection zone. The local equipotential connections must be connected to each other, and finally to the main equipotential connection.

3. Set up lightning protection zone

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

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

The function of the lightning protection device is to connect the protected system to the equipotential system in the shortest time (nanosecond level), so that each port of the equipment is equipotential. At the same time, the huge pulse energy generated by the lightning strike in the circuit is released to the ground through the short-circuit line, reducing the potential difference of each interface end of the device, thereby playing a role in protecting the device.

The LED street light power module must not only be designed in accordance with 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 shall be tested according to GB19510.12 / IEC61347-2-13 safety standard.

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

3. If a control device has the functions of the above two, it should be tested according to the safety standard of GB19510.12 / IEC61347-2-13.

Practice has proved that through scientific design and strict inspection, not only can the LED street light system be protected from lightning, but also can prevent the common mode and differential mode interference of the lightning to the power supply equipment.