Surge protection concept for LED street lights
By B Leibig and D Dürr, DEHN + SÖHNE
Electricity + Control, June 2015 (pages 22 – 24)
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Luminaire manufacturers and users such as municipal utilities or communities can often not find the cause of damage. Therefore, the consequences of damage become evident in 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 negatively affect its lifetime. Consequently the predicted lifetime cannot be ensured in practice and the LED light must be replaced earlier.
These unscheduled costs lead to additional expenses and usually have not been considered in the amortisation of the project. Now the question arises to what extent the manufacturer assumes warranty for the LED light (LED drivers and LED modules). Although the lighting industry has responded to this problem with a higher dielectric strength of the LED drivers of new LED lights, the impulse currents and surges occurring in practice often considerably exceed the typical dielectric strengths of 2 kA to 4 kV of the LED lights many times over.
In this case, it must be observed that the types of surges between L to N (differential-mode interference) and L/N to PE (common-mode interference) significantly differ and particularly the cause of damage L/N to PE is often not taken into account by the designer owing to the ‘double or reinforced insulation’ (previously class II) of the LED light.
- LED street lights are sensitive to voltage surges.
- Appropriate protection topologies must be selected based on the actual system configuration.
- All protection strategies must be confirmed with laboratory testing.