Street lights are installed outdoors, and lightning strikes are a very big threat. If it is light, the street light will be damaged, and if it is heavy, it will cause fire or human casualties and cause huge losses. Here, we will introduce to you about the impact of lightning on LED street lights and preventive measures.
This article summarizes the following four types of lightning strikes:
1. Direct lightning
Directly enlightening Lei Yun contains a great deal of energy, peak voltage up to 5000kV lightning current into the ground, with great destructive power. It will have the following three effects:
A huge, rich current flows down the ground in a few microseconds, rapidly picking up the ground potential, causing a counterattack and endangering the safety of people and equipment.
b Lightning currents generate powerful electromagnetic waves, which induce extremely high pulse voltages on power lines and signal lines.
c Lightning currents flow through electrical equipment and generate extremely high heat, causing fire or explosion.
2. Conduction mine
The remote lightning strikes the line or the extremely high voltage generated by electromagnetic induction is transmitted from the outdoor power line and the communication line to the electrical equipment inside the building.
3. Induction mine
Frequent discharges between clouds generate strong electromagnetic waves that cause common-mode and differential-mode interference, affecting the operation of electrical equipment.
4. Switch over voltage
Inductive and capacitive loads in the power supply system are switched on or off, ground short circuit, short circuit in the power supply line, etc., all 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. . Damage effects are similar to lightning strikes.
So how do we prevent lightning accidents? According to a study by the China Power Huaxing Power Supply Research Laboratory, the following methods are the most effective ways to prevent street lighting from being destroyed by lightning:
4.1 The combination of external lightning protection and internal lightning protection
Now the general exterior of the LED street lamp is a conductor material, which itself is equivalent to a lightning rod. In the design, the down conductor and the ground net must be installed. These systems constitute an external lightning protection system. The system can avoid the fire and personal safety accident caused by direct lightning strikes on LED street lamps. The internal lightning protection system means that the interior of the street lamp is protected by means of grounding, voltage protection and other means. The system can prevent inductive lightning and other forms of over-voltage intrusion, resulting in power destruction, which is not guaranteed by external lightning protection systems. The two are mutually reinforcing and complement each other. The internal lightning protection system must be connected to an external lightning protection system or an overvoltage protection device on many devices such as the enclosure, cables to and from the protection zone, metal pipes, etc., and be connected equipotentially.
4.2 lightning protection equipotential bonding
Eliminating the destructive potential difference due to lightning, power lines, signal lines, metal pipes, etc. must be protected by equipotential bonding using an overvoltage protector. Local equipotential bonding is also required at the interface of each inner protection zone. The equipotential bonding sites are connected to each other and finally to the main equipotential bonding site.
4.3 Setting lightning protection zone
In addition to power supply equipment, LED street lights will also be equipped with some communication devices for controlling the switch and brightness of street lights. These devices and power supplies need to be placed in the lightning protection zone. The protection zone is directly shielded by the enclosure. The electromagnetic field here is much weaker.
4.4 High-quality protection equipment - lightning protection module and overvoltage protection module
The function of the lightning protector is to connect the protected system into the equipotential system in the shortest time (nanoseconds) to make the equipment equipotential. At the same time, the huge pulse energy generated by the lightning strike in the circuit is released to the ground via the short-circuit line, which reduces the potential difference at each interface end of the device, thereby protecting the device. The CLP China Star R&D team believes that the LED street light power module must not only be designed in accordance with the above requirements, but also must undergo a rigorous inspection procedure.
a Control device with a constant voltage output function or a constant current output function or both, should be tested with the safety standard GB19510.12/IEC61347-2-13.
b For control devices that only have the function of controlling logic dimming, flashing, color, etc. of the LED, the GB19510.12/IEC61347-2-11 safety standard shall be used for inspection.
c If a control device has both the above-mentioned functions, it shall be tested in accordance with the safety standards of GB19510.12/IEC61347-2-13.
5 Conclusion
Practice has proved that through scientific design and rigorous testing, it can not only ensure that the LED street light system is not damaged by lightning, but also eliminates the common mode and differential mode interference caused by lightning to the power supply equipment.
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