Protecting LED lighting from power surges
LED technology has become prevalent in many areas due to its long service life and high energy efficiency. To prevent damage in the event of an error and to protect investment in LED technology, a comprehensive power-surge protection strategy cannot be overlooked, even in street lighting.
LED modules have made lights much more compact and they can be dimmed and adapted to the needs of the user by means of sensors, but they are inherently more sensitive to power surges than conventional lighting. The destruction of sensitive control drivers and LED modules by power surges reduces cost savings — not least because the cost of replacing the equipment is much higher than for replacing conventional lighting technology.
For LED lights to operate safely and efficiently long term, all of the installation components must be carefully selected. Professional lightning-current and power-surge protection is recommended for all types of lighting: interior, exterior, tunnel and object lighting.
Suitable safety devices increase the LED equipment’s service life and contribute to personal and system safety. They also reduce maintenance and repair costs.
In order to protect the expensive components from premature failure, Phoenix Contact has developed special lightning current and surge voltage arresters for a safety strategy that is attuned to the application.
Power surges and their consequences
Power surges in street lighting have various causes:
- Direct lightning strikes to the lights, the power supply cables or the street lighting peripheral equipment.
- Indirect lightning effects due to capacitive or inductive coupling in the power supply cables.
- Switching operations due to ground faults, short-circuits or triggered fuses.
Whether a partial or complete failure is produced depends on the energy density of the current pulse and the sensitivity of the components to power surges. It is also possible for LED lights to sustain damage from a power-surge event and still remain functional, but this usually reduces the service life of the lights.
Lightning strikes near the lights can generate voltages of up to several tens of thousands of volts in the lines. Lightning striking a building that has external lightning protection, for example, or even a tree in the area, creates a voltage gradient and the ground potential rises to several thousand volts.
The magnitude and intensity of a power surge depends, in turn, on the lightning intensity and internal resistance of the soil. If the insulation strength of the components is exceeded, the insulation breaks down at the weakest spot. Electronic devices, LED modules, power supply cables and/or cable junction boxes are damaged or destroyed. Insulation failure always poses a lethal risk and in the worst case can lead to electric shock if there is contact with metallic parts such as a light pole.
Power surges can also be generated by capacitive or inductive coupling in the power supply cable — the cause here is the lightning current flowing to the ground. Thus, for example, the current flow into the down-leads of exterior lightning protection systems generates an electromagnetic field around itself, which in turn induces power surges in power supply cables arranged in parallel.
Such effects must also be taken into account for a direct lightning strike to a tree, which, under unfavorable circumstances, can also lead to street lighting failure. A comprehensive lightning-current and power surge protection strategy also protects the LED lights from power surges — and thus increases the availability.
What does a suitable protection strategy look like?
A multistage power surge protection strategy for a street lighting system based on LED technology focuses on three installation locations:
- Directly in the LED lighting.
- In the cable junction box at the base of the pole.
- In the power supply cable distribution boxes.
(1) directly in the LED light, (2) in the cable junction box at the base of the pole and (3) in the cable distribution boxes for the power supply.
The protective ground conductor in a Lightning Protection Class II LED light with doubled or reinforced insulation must not be connected. This is because there are suitable power surge protection devices between the phase (L) and neutral (N) conductors.
The current European product standard for lights, IEC 60598-1, which applies to protection classes I and II, states that for Protection Class II stationary lights, the power surge protection devices must not be connected to ground or the metallic light housing. In contrast, in Protection Class I lights, power surge protection devices may be installed in accordance with IEC/EN 61643-11. In Australia and New Zealand, the surge protection standard is AS/NZS 1768:2007 and the AS/NZS 3000 wiring rules detail the correct installation techniques.
The cable junction box is also suitable for installation of the power surge protection device. The advantage relative to an installation in the light is that the protective ground conductor also goes into the cable junction box. Intended for connecting to ground, it can also be used for Protection Class II LED lights. This provides effective protection against transient power surges. Another advantage is easy access for inspection or retrofitting. The retrofitting of suitable power surge protection is often neglected for cost and time considerations.
High wiring flexibility
The power surge protection devices from Phoenix Contact’s Blocktrab product family are suitable for both installation locations. Their compact design allows them to be easily integrated into the existing installation. Therefore, light manufacturers and installers of new installations and light retrofits are not restricted in terms of cable lengths, cross sections and colours.
The reinforced insulation means that the protection devices can be used in Protection Class II LED applications without additional measures. For grounded systems, a protection device with a protective ground conductor connection is provided. The status of the protection devices is indicated directly on the device, and the signal can be transmitted to the lamp via the so-called ‘L’ connection. If the power surge protection device’s disconnect device is triggered due to an overload, the light is also switched off. This considerably simplifies routine inspection of the power surge protection devices.
The protection devices are designed with a lower protection level — (L-N) < 1.3 kV — for typical LED applications. This is because the protective effect is given only when the protection level of the power surge protection device is below the impulse withstand voltage of the light and the LED driver. The power surge protection devices from the Blocktrab product family have been inspected by Dekra for quality and safety and have received KEMA approval according to the current IEC/EN 61643-11. Thus the user not only benefits from increased security, but enjoys a financial advantage with additional approvals for the LED light.
The lighting industry has made great advances in energy-efficient LED technology. However, because this technology is more sensitive against power surges than conventional lighting technology, specific protective mechanisms must also be included. These will increase the service life of the LED lights and ensure that the new technology is a good long-term investment.
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