Older methods of outdoor lighting have relied upon metal halide and high-pressure sodium solutions that are quickly being replaced by new options containing LED technology. Initial cost of installing outdoor LED lighting can be substantial, however this cost is justified and offset (roughly over five years) by lower energy consumption, longer overall lifetime and lower maintenance cost. Key to meeting the lower maintenance costs is providing the right level of lightning surge protection.
Do LED Lights Need a Surge Protector?
Outdoor luminaires are susceptible to transient spikes caused by lightning strikes that are inductively coupled onto power. The older methods of lighting, such as mercury vapor, metal halide or sodium vapor lights, relied upon their robust construction to suppress any transient voltage spikes. LED lighting isn’t afforded that luxury and voltage transients can destroy LED power supplies as well as the LED’s themselves. Due to the sensitive nature of LED lights, numerous studies have been conducted and resulted in the creation of multiple standards which characterize the lightning surge hazards. Two different exposure levels for outdoor locations are categorized by IEEE C62.41.2™-2002 (Category C Low and C High) with different suggested surge levels for each. Similarly some countries or even regions within those countries may have different requirements based upon lightning strike densities for those particular areas.
Surge Protection for LED Drivers
The most common type of surge protector contains a component called a metal oxide varistor or MOV, which diverts the extra voltage away from the device it is protecting.
MOVs are widely used in surge protection circuits because of their fast response times, high surge energy capability, cost effectiveness and compact size. However after MOVs are subjected to numerous surge strikes they begin to degrade and are unable to provide the same protection as new ones. Although MOVs tend to degrade slowly, one large or several small surges can cause failure. As MOV’s degrade, the leakage current increases, thus raising the temperature of the device and potentially driving the MOV into thermal runaway (where catastrophic failure may result in smoke and fire). This makes it necessary to have a thermal disconnect in series with the MOV that will disconnect the circuit prior to smoke or fire. If the MOV and the thermal fuse element are integrated into a surge protection device (SPD) module rather than designed as part of the LED power supply circuit, then only the SPD module would need to be replaced after multiple surge events cause the device to fail.
Littelfuse’s innovative modular approach with the surge protection circuit being separate from the power supply not only allows replacement of just the module at end of life, it also allows the same luminaire to easily be marketed globally with a simple switch of the surge protection module to meet “local” requirements. Additionally, the module may offer protection to the LED driver during any installation mishaps that could cause the MOV to go into thermal runaway (ie loss of neutral or incorrect wiring). The surge protection device (SPD) module with its thermal protection circuitry will simply disconnect and may prevent damage (configuration dependent) to the rest of the luminaire.
Series vs. Parallel Surge Protection
Luminaire designers can choose from two main types of SPD module configurations based on their maintenance and warranty strategies. Those are parallel- and series-connected surge protection subassemblies. Littelfuse offers solutions for both configurations with its LSP05 and LSP10 surge protection module line.
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SPD Module in Parallel Connection
The SPD module is connected in parallel with the load. An SPD module that has reached end-of-life (thermal protection circuitry has caused the circuit to open) is disconnected from the power source while leaving the power supply module and LED driver module energized. The lighting is still operational, however protection from the next transient surge offered by the CSP to the power supply and LED modules is lost. In a parallel-connected SPD module, a small LED indicating the status of the SPD module can be added to alert the maintenance technician as to the status of the SPD. Options for a green LED (normal operation) and a red LED (end of life) provide a visual indication at each location of the need for maintenance. Alternatively, to the visual LED indication at each separate lighting fixture, the need for an SPD module replacement could be communicated remotely to a master light management center by connecting the SPD end of life indication wires through a networked smart lighting system. The latter offers a much cleaner monitoring solution.
SPD Module in Series Connection
The SPD module is connected in series with the load, an SPD module that has reached end-of-life (thermal protection circuitry has caused the circuit to open) is disconnected from the power source which disconnects the power supply module as well as the LED module which in turn, shuts the light off. In a series-connected SPD, the loss of power (and resulting loss of light) to the luminaire serves as indication for a maintenance call to replace the SPD module. Note that since both the power supply and LED modules are disconnected, any future transient surges will not cause damage to either module. Preference for this configuration is growing rapidly since the luminaire investment in the LED and Power modules remains protected while awaiting replacement of the series-connected SPD module. It is much less expensive to replace just the series connected SPD module rather than the entire luminaire system as in the case of a parallel-connected SPD module that has a damaging surge occur prior to SPD module replacement.
Conclusion
The creative approach of breaking luminaire design into modules allows the luminaire designer a large degree of flexibility in the approach to system design. The modular approach allows designing to multiple voltages with different protection levels depending upon geographical location. Additionally, this inventive technology provides visual indicators of module failure while allowing fast disconnect ability between the SPD module and the power supply\light engine, fostering easy maintenance by a service technician.
Outdoor LED lighting is the wave of the future for roadway lighting, digital signage, traffic lights and parking garage lighting due to lower wattage requirements, longer overall lifetime and lower maintenance cost. Littelfuse Surge Protection Modules will not only increase the reliability of these systems but also extend the life of the power supplies and light engines by providing solid protection from transient surges.
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