Outdoor LED lighting

Sensitivity to surge

LED-technology luminaires containing electronic components are sensitive to surge, which will attack the power supply drivers and LED components and therefore drastically reduce the luminaires’ theoretical lifetime.

The effects of lightning strokes can be approached in two ways: when the component examined is the one which receives the lightning, this is a case of a direct lightning stroke, and when the component examined merely sustains effects, this is an indirect lightning stroke.

[a] Radiation
[b] Conducted
[c] Direct
[d] Rise in earth potential

Fig. N51 – Direct and indirect lightning strikes

Surge generated by lightning

The atmospheric phenomenon of lightning is due to the sudden discharge of the electrical energy accumulated in storm clouds.

• Direct lightning stroke: when the lightning falls on a structure, the lightning current generates a pulse surge.
• Indirect lightning stroke: this is the remote manifestation of a direct lightning stroke. Its effects are presented here from three aspects: conducted surge, rise in earth potential and radiation.

Note: Refer also to Overvoltage protection.

Fig. N52 – Type 2 surge protection device

Temporary Overvoltage

The main characteristic of these surges is their frequency which assumes that of the network: generally 50 Hz or 60 Hz.

Types of surges are called TOV (for Temporary Over Voltage). These TOV could be generated by a fault on power system, neutral breaking for example: although distribution networks are normally three-phase, many switchgear items are single-phase. Depending on the needs of each low voltage consumer, voltage unbalances may occur. The most problematic case is breaking of the neutral which may generate a rise in potential that is harmful for devices programmed to operate at single-phase voltage and which then find themselves operating at a voltage close to phase-to-phase voltage.

Fig. N53 – Surge arrester for information circuit

Outdoor LED installation protection

Protection against transient surges

Surge protection devices must be used in order to protect public outdoor LED lighting installation.

An entire range of surge arresters is thus available: modular arresters for mounting on a symmetrical rail, arresters that can be installed in a main low voltage board or in luminaire enclosures. They all enable flow off of various currents with a varying voltage protection level.

In addition, surge arresters for information circuit must be used. They must be adapted for two low-current lines without common potential used in public lighting.

The input current must not exceed 300 mA.

Fig. N54 – Voltage threshold tripping device

Protection against TOV by voltage threshold tripping device

The protective device will trip when the voltage across its terminals exceeds its nominal value.

Miniature circuit breaker, surge protection device and voltage threshold tripping device are available in an complete integrated product (see Fig. N55).

Fig. N55 – Miniature circuit breaker, surge protection device and voltage threshold tripping device

Conclusion

The complete installation protection (with zero-crossing contactor, surge protection devices and voltage threshold tripping device) is represented on Fig. N56.

We can see on Fig. N56 that surge protection devices are installed in the streetlight main switchboard and in the junction box located in the bottom of the lighting columns. These protections are easily accessible for service. In case of failure, replacement is quick and easy.

The connection of the metallic lighting columns to the earthing system allows the adjustment of different parts of the lighting system to the same potential, thus reducing significantly the overvoltages that occur on the luminaires.

Fig. N56 – Outdoor LED lighting protection