Company Announcement - The retrofitting of street lights in communities and municipalities with LEDs is on the rise, due to energy efficiency, the removal of certain lamp technologies from the market, and the long lifetime of LED technology. A well-conceived surge protection concept for LED lights should be incorporated at the design stage, where the foundations for an efficient protection concept should be laid to ensure longevity and availability and to avoid unnecessary maintenance. Although LED technology has many advantages, a shortcoming over older luminaire technologies is that replacement costs for equipment are higher, and also that LEDs are more susceptible to surges.

Surges can be caused by:
• Direct lightning strike to the luminaire, supply line or periphery of the street light; or
• Indirect lightning strike which causes conducted interference in the supply line as a result of capacitive or inductive coupling; or
• Surges resulting from switching operations, earth faults /short-circuits or tripping of fuses.
An analysis of surge damage to LED street lights has shown that, in the majority of cases, several LED lights are affected, not just the one that has been struck.

Luminaire manufacturers and users, such as municipal utility companies, frequently cannot find the cause of damage, with the consequences of the damage only becoming evident in the partial or complete failure of the LED modules, destruction of the LED drivers, reduced brightness or failure of electronic control systems. Even if the LED light is still operational, surges normally affect its lifetime negatively. Consequently, the predicted lifetime cannot be ensured in practice and the LED light must be replaced sooner. These unscheduled costs lead to additional expenses and are usually not considered in the amortisation of the project.
Laboratory tests undertaken by DEHN + SÖHNE, in co-operation with LED light manufacturers, and the practice-oriented system test of a complete LED system, in conjunction with practical experience have aided the company in designing an efficient protection concept for LED street lighting systems. A well-founded protection concept can only be implemented by means of a complete system, consisting of cascaded surge protective devices in the cable distribution cabinet and the cable junction box or in the LED light.

The cable junction box is ideally suited for integrating surge protective devices. On one hand, all protective paths can be protected by a surge protective device even if a lighting fixture with double or reinforced insulation is used, ensuring maximum protection against transient overvoltages. On the other hand, this area is more easily accessible for retrofitting and maintenance purposes. Moreover, the earth potential of the steel mast can be connected to the cable junction box on the earth side to create a common reference potential.

Depending on the design, different type 2 surge protective devices, such as the compact DEHNcord arrester or DIN rail-mounted devices such as DEHNguard, can be installed. To ensure protection against transient overvoltages resulting from indirect lightning effects or switching operations, which are relatively common in the vicinity of the transformer, and against direct lightning effects from the distribution network, it is advisable to install type 1 + type 2 combined arresters in the cable distribution cabinets. Depending on the requirements concerning the lightning current to be discharged, DEHNventil or DEHNshield arresters can be used.

Finally, a coherent earthing concept, where all metal masts must be connected to the protective conductor of the surge protective devices used, should be considered. This allows safe control of potential differences and ensures the availability of the LED street lighting system also in case of surges. This is the only way to ensure that an investment for retrofitting street lighting systems with the new LED technology achieves the predicted lifetime and uncalculated follow-up costs are prevented.