LED street lamp lightning overvoltage protection analysis and countermeasures

- Jul 29, 2019-

LED light sources and associated electronic controls or drives bring many benefits to outdoor area lighting applications, such as long service life, reduced maintenance and controlled beam, but the environment for outdoor applications is harsh. In contrast to indoor lighting, in street lighting, potential overvoltages or surges must be addressed.

Running and maintaining public lighting accounts for most of the government's energy costs, but much could be saved by replacing traditional sources with LED lights. But unlike traditional light sources, leds that run at low voltage and the electronic controls that drive leds are more susceptible to overvoltage. Therefore, only when sufficient attention is paid to protect LED street lamps from the influence of overvoltage, can the transformation of outdoor solid-state lighting be successful.

Small overvoltages have little effect, but frequent overvoltages may adversely affect the life of LED light sources. Large overvoltages, such as those generated by lightning strikes, are likely to immediately destroy the LED modules or electronic control devices of multiple LED street lamps.

Lightning is still a major risk

Overvoltage is a greater risk to the reliability of street lamp operation

Lightning surges are harder to calculate.

· protection type

Due to changes in the environment, the industry has developed different protection levels for the design of LED lamps. The LED lighting system includes the lamp housing (also known as the lamp holder of the street lamp), the LED module of the optical system (lens, reflector) and the electronic control device that provides the appropriate power for the LED module.

In the lamp design of the protection class I, all conductive parts are explicitly connected to the safety ground wire. However, for historical reasons, most street lighting in Europe falls under category II protection. In class II protection class lamps, all live parts have a protective insulation, but are not explicitly connected to a safety ground wire. Surge protection devices (arrester) shall not compromise the protection insulation, even during short lightning strike times. Therefore, it is not possible to provide optimal surge protection in the form of conductors connected to metal casings or grounding wires in class II protected lighting equipment.

In protection class II, lamp heads made of metal are designed differently from lamp heads made of non-conductive materials. When designing a metal luminaire head, it is best to provide an equipotential connection between the controller and the LED module to prevent potential resistance and thus increase the surge voltage. Even if the lamp head is connected to the ground through the mast, there may be high or uncertain impedance, and the system must provide appropriate insulation according to the class II protection grade.

If the lamp head is made of non-conductive material, all exposed parts must also be made of non-conductive material or insulated according to class II protection grade. You don't need an equipotential connection here. The weakest link here is the LED module, which, depending on the insulation material and its thickness, provides 10 kV surge protection. Without reliable surge protection, the light source may age prematurely or even fail completely.

- recommendations for surge protection

Surge protection requirements of up to 10kV in secondary protection lamps are increasingly being used in tenders for street lighting projects, according to Germany's central electrical and electronics industry association. If there is an option to convert the lighting to protection level I, then this is the best solution.

In addition, LED lamps also have high-quality drivers, in the driver to achieve surge protection methods are many. Based on different capacitors, ruijie has developed a special voltage distribution device in the driver to ensure that the maximum output of the driver is only 500V, even in the case of high input transients. Most of the voltage can be consumed from the source to the output. For areas with low or average lightning frequency, a 10 kV control provides high surge protection. Previously this could only be done by adding surge modules to the illuminator head, but this is no longer allowed with class II lamps.

● coping Suggestions

For areas with high lightning strikes, it is recommended to install an overvoltage absorber in addition to a strong driver design in the main power distributor, or if the distributor is too far away, in a cable junction box. These external overvoltage devices must be tested in accordance with EN 61643-11 and matched to the integrated surge protection in the luminaire.

In addition, lighting developers and even city and utility managers should ensure that the drivers installed in street lamps are compatible with the local environment.