Surge protection for LED lighting systems

Causes of overvoltages and their effects on lighting systems

Overvoltages have a highly destructive effect on electronic devices, including LED lighting systems. They cause premature wear and tear on LED drivers and LED modules, and can even lead to total failure of the lighting system.

Due to their exposed location, public lighting systems are highly susceptible to challenging environmental influences. They are directly exposed to nearby and distant lightning strikes and overvoltages, so in locations where continuity of operation is critical, these systems must be protected against lightning strikes and overvoltages.

Of the causes of overvoltage listed in international protection standards, the probability of a public lighting system being affected is greatest:

• Direct lightning strikes on distribution lines (conducted through power lines)
• Lightning strikes near a building/structure (induced surges)

However, the dangers of overvoltage should not be neglected in building technology either. In industrial and sports facilities, lights are usually installed at very high heights. In the event of damage, if the lights fail, the required minimum illuminance cannot be achieved, which can lead to an increased risk of accidents. In addition to the hardware costs, replacing the defective components also incurs high costs due to the use of lifting platforms and service personnel, as well as potentially costly downtime (e.g., in industrial production facilities).

In order to prevent potential hazards and damage and thus ensure the operation of the systems, appropriate investments in lightning and surge protection must be taken into account. The use of suitable surge protection devices (SPDs) can extend the service life of lighting systems, improve public services, and significantly reduce overall operating and infrastructure costs.

The vulnerability of electronic lighting systems to surges is widely recognized in the technical literature, and various international regulations and standards stipulate the need for appropriate lighting protection.

IEC 60364-1 requires protection against lightning and surges for people, livestock, and property. In addition, the need for protection against the effects of lightning strikes can be determined by a risk analysis in accordance with the lightning protection standard IEC 62305. The lighting standard IEC 60598-1 Luminaires Part 1: “General requirements and tests,” point 4.32 specifies: “Surge protection devices must comply with IEC 61643-11.” It is crucial for the protective effect that the protection level of the surge protection device is below the surge resistance of the luminaires and the LED driver.

What are transient overvoltages and how do we protect LED equipment from them?

Overvoltages in electrical power supply systems can be caused by various factors and can lead to damage or failure of LED lighting systems. Lightning strikes and switching operations typically cause transient voltage spikes that can reach tens of thousands of volts but last only a few microseconds. Despite their short duration, their high energy content can cause serious problems for electronic devices connected to the power grid, as the voltage spikes are usually well above the impulse voltage resistance of the connected electrical equipment (LED lights). The consequences range from premature aging to destruction, leading to operational interruptions and costly repairs.

A few years ago, the surge resistance of street lights was around 2–4 kV, but today it averages around 4–6 kV. High-quality lights even offer impulse voltage resistance of up to 10 kV.

However, this is often not sufficient, as can be seen in Figure 1, especially since the impulse voltage resistance of the luminaires is usually defined by the so-called passive overvoltage protection provided by the LED control gear.

Figure 1: Possible causes of overvoltages and their magnitude, as well as the rated impulse voltage according to EN60664-1 / VDE 0110.

As mentioned above and shown in Figure 1, transient overvoltages in power supply systems can be triggered by various causes. For example, lightning strikes that hit a building's distribution line or its lightning conductor directly can induce electromagnetic fields that generate voltage spikes in nearby lighting systems. Long outdoor power distribution lines are very susceptible to the direct effects of lightning strikes, as large currents are conducted from the lightning into the power lines. In this case, we refer to so-called lightning surges. Lightning strikes can reach very high values depending on the distance of the strike location, the ground and earthing conditions, and the strength of the lightning. Figure 2 shows the qualitative influence of a potential funnel on the light points of street lighting when lightning strikes nearby.

Figure 2: Possible overvoltage load on light points in the event of a nearby lightning strike

However, even phenomena that are not weather-related can cause voltage spikes in adjacent lines, e.g. switching devices (contactors) in control cabinets or the shutdown of transformers, motors, and other inductive loads or high-power devices (generators, welding equipment) that couple energy into common branch circuits connected to sensitive electronic equipment and place a heavy load on them (see Figure 3).

Figure 3: Overvoltages caused by switching operations in the network. E.g., tripping of fuses, switching of inductive loads, ground faults and short circuits, magnetic ballasts in mixed networks, etc.

In this case, we are talking about so-called switching surges, which are caused by “switching operations in the network” and can reach values of several thousand volts.

A typical example in lighting technology is the tripping of fuses or mixed networks with LED and conventional discharge lamps with conventional ballasts, which provide several thousand volts of ignition voltage.

Electrostatic discharges (ESD) are a phenomenon that occurs particularly in protection class II luminaires, where charge separation takes place (Figure 4) and subsequently a high static voltage can build up on the luminaire housing or heat sink of the LED, which can then discharge uncontrollably in the luminaire and damage the LEDs or the LED driver. Lights that are operated completely isolated from earth potential are particularly affected. Examples include SK II lights on GRP and wooden poles or rope suspensions. The LED lights commonly available on the market do not usually offer sufficient protection against this phenomenon and should be equipped with appropriately designed protective devices to prevent consequential damage from ESD.

Figure 4: Left - Electrostatic charge in insulated housing (SK II);
Right - Prevention of static charges by installing an MLPC2-230L-V/ESP

Mains faults can lead to so-called temporary overvoltages. The most common cause of this is a drop in the neutral conductor, e.g. due to damage. In the event of this fault, the rated voltage can increase to up to 400 V on the phases due to mains imbalances in the 3-phase mains (Figure 5). Protection against temporary overvoltages requires special consideration because, unlike transient overvoltages, they can last significantly longer and therefore cannot be handled by conventional surge protection devices. Citel offers special devices from the -VM-series for this purpose.

Figure 5: Temporary overvoltages due to neutral conductor failure

But there are also problems with building and hall lighting. This is particularly the case where surges do not originate externally, but daily from the building's own system. There are known cases, particularly in industry, where electrical equipment generates surges that are transmitted to the lighting via the electrical cabling. The first sporadic failures of individual lights or LEDs are typical signs of this.

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Effective protection concept

In general, the most effective approach to protecting large lighting installations from surges is to cascade multiple levels of protection. Each level provides the necessary balance between discharge capacity and voltage protection level. In this way, a first stage (typically a Type 1 or Type 2 SPD) provides robustness and dissipates most of the energy from a surge, while a second stage (typically a Type 2 or Type 3 SPD) provides “local” protection. The peak voltage and peak current reaching the equipment always remain below the critical value. Each installation has its own specific characteristics (properties) – therefore, SPD solutions should be tailored accordingly and include appropriate lightning protection and grounding systems. Properly executed ground connections are essential for the effective functioning of a lightning protection system. The grounding connections must ensure proper contact in accordance with industry standards for the construction of electrical installations. The connection resistance must be low, and the conductivity of the grounding material must allow for efficient dissipation of the surge energy.

The following components are therefore relevant for an effective protection concept against transient overvoltages: A. Street lighting main distribution board (control cabinet | main distribution) B. Mast fuse box in the mast (UV / sub-distribution) & luminaire(s)

CASE 1.) Streets and outdoor lighting:

Figure 6: Protection concept for street lighting: Type 1+2+3 combination arresters in the switchgear; Type 2+3 surge protection devices at the light points (in the pole and/or luminaire head)

Street lighting main distribution board:

High-quality type 1+2+3 combination arresters can be installed in the main distribution board to protect the central power supply where there is a good protective earth connection. This protects the main distribution board and thus the entire street from total failure. The lights are also indirectly protected (relieved) by centrally limiting a large part of the transient overvoltages from the power grid. Good potential equalization between the light points and the main distribution board maximizes the protective effect.

Street lighting points:

IEC61547 states that all luminaires should be protected against overvoltages up to 1 kV in differential mode and 2 kV in common mode (standard protection at luminaire level).

In addition, protection up to 10 kV is recommended. The protection of individual light points depends on the respective situation. In principle, it is possible to install a powerful type 2+3 surge protection device (SPD) in the mast fuse box or in the luminaire. As a rule, one protection device is sufficient. Since mast heights usually do not exceed 15 m, a good level of protection can already be achieved by installing the device in the mast fuse box.

Many luminaire manufacturers offer their customers the option of protecting their luminaires with an integrated SPD. If this is not possible or desired, e.g., due to space constraints or because the luminaires are already installed in the field, the SPD can always be installed in the mast fuse box.

The most sensible solution therefore depends on the local conditions.

The following points are therefore relevant when finding a solution:

• Luminaire protection class: I or II
• Space available in the luminaire or in the mast safety box
• Accessibility for maintenance purposes
• Retrofitting or new installation

The question of maintenance options and the possibility of retrofitting existing systems are particular arguments in favor of installation in the mast safety box. The slightly better level of protection and lower installation costs are arguments in favor of installation in the luminaire.

With protection class I luminaires, the lighting operator always has the option of installing surge protection devices in the luminaire or in the mast fuse box, as a protective conductor is available throughout and electrical safety is guaranteed in all cases.

According to lighting standard IEC 60598-1, surge protection devices in accordance with IEC 61643-11 must not override the protective insulation in Class II luminaires. Optimal surge protection against the metal housing or earth is therefore not possible in a protection class II luminaire. Only protection between L and N (in what is known as differential mode) is possible without restriction. In the case of metal masts, there would therefore be no effective protection if the earth potential increased due to nearby lightning strikes.

Installation in the mast safety box is possible in compliance with electrical safety requirements according to IEC 60364-4-41 “Erection of low-voltage installations - Part 4-41: Protective measures - Protection against electric shock,” provided that the mast itself is not part of protection class II. In many lighting installations, there is a protective conductor in the mast fuse box that allows the mast and a surge protection device of protection class I to be integrated into the protective equipotential bonding. Electrical safety, especially the shutdown conditions, is achieved by connecting the protective conductor and the fuse that is usually present in the mast fuse box. If the impedance of the protective conductor is not good enough, as is the case with TT networks, for example, RCD switches must be installed in order to achieve the necessary shutdown times in accordance with IEC 60364-4-41. The conductive connection of the luminaire to the metal mast also allows luminaires of protection class II to be effectively protected against lightning surges.

The protection of lighting control systems must not be forgotten. Lighting control systems such as control phase, DALI, 1-10V, DMX, etc. must always be included in the protection concept. These are usually even more sensitive than 230V~ systems and are generally not protected by the ECG. In this case, we recommend combined surge protection solutions for 230 V and lighting control in a single device to protect the luminaire (see Figure 9).

CASE 2.) Building technology:

In building technology (Figure 10), effective protection can be achieved by equipping the electrical installation with suitable lightning and surge protection devices. For example, type 1+2+3 combination arresters can be used in the building feed to protect against lightning currents and mains transients, and type 2+3 SPDs can be used in the lighting sub-distribution boards and luminaire connection boxes to protect against field coupling and switching surges.

Practical surge protection

When selecting surge protection devices, particular attention should be paid to the following points:

1. Good surge protection should be tested and certified in accordance with IEC 61643-11 and meet the requirements of VDE 0100-534. To achieve this, status indicators and disconnecting devices are integrated into the SPD, among other things. These enable maintenance personnel to easily perform a visual inspection to determine whether the SPD is still functional. Regular inspection is essential.
2. Since the SPD is usually installed in inaccessible locations, such as in luminaires, purely visual signaling is not ideal. An SPD that can also disconnect the luminaire from the circuit in the event of a fault offers a good and simple option for indirect signaling. The size and mounting type of the SPD must meet the requirements of the installation location.
3. If moisture or dust is present, an SPD with a higher IP rating should be selected.
4. SPD must take into account the protection class (SKI or SKII) of the luminaires.
5. SPD must be designed for the exact rated operating voltage of the system. An SPD designed for a higher operating voltage does not offer better protection.
6. Low protection level; ≤1500V, lower is better
7. In addition to protection for the 230 V supply, protection for the control system, such as DALI, second (control) phase, 1–10 V, or DMX, should be taken into account. SPDs that combine AC and control are ideal for these luminaires and usually offer better coordinated protection than two individual SPDs.

When installing SPDs, always follow local electrical regulations and the SPD manufacturer's instructions.

Active surge protection vs. voltage resistance:

A key advantage of active surge protection devices is that they operate independently of the level of surge voltage. An SPD functions like a voltage-controlled switch. If the surge voltage is lower than the SPD's activation voltage, the component is passive. However, if the surge voltage exceeds the activation voltage, the SPD diverts the surge energy and prevents it from damaging the equipment. When selecting the appropriate surge protection device, the maximum energy absorption rating is of crucial importance. The lightning impact on the device must be taken into account, as well as the maximum surge voltage that the device must withstand. It is important to consider the type of surge protection device, the installation situation, and the risk to the system or persons.

If, on the other hand, the insulation or dielectric strength of a luminaire without active surge protection is exceeded, total or at least partial failure of the luminaire is usually to be expected. In order to test how well current luminaires are protected against overvoltage (passive surge protection) and what additional benefits active surge protection components offer, a field test was carried out on luminaires from various well-known manufacturers. First, the luminaires with standard surge protection were subjected to 15 pulses of up to 10kV/5kA, and then the same test was repeated with upstream surge protection.

While the lights failed in rows during the tests without upstream surge protection because the test pulses exceeded the pulse resistance of the lights at a certain level, not a single failure of the tested systems was recorded during the tests with upstream surge protection devices, even at a pulse voltage of 10kV (Figure 11a). The simple explanation: Unlike “passive” surge protection, where the surge resistance is set to a specific maximum voltage level purely by design, the active surge protection device limits the voltage to acceptable values (Figure 11b) and the generated impulse current is safely dissipated by the surge protection device.

Figure 11a) (1,2/50µs) Impulse

Figure 11b) Voltage limitation and leakage current (8/20µs) through the SPD

Conclusion

LED technology is establishing itself as the new standard in lighting. Further developments in this technology are resulting in increasingly efficient and reliable solutions. Practical, customized surge protection devices and protection concepts (Figures 6 and 10) protect sensitive electronics from harmful surges. The additional costs of an effective surge protection concept for a lighting system currently amount to less than one percent of the total costs. Surge protection measures are therefore a simple and often indispensable means for every system operator to maintain the long-term service life and reliability of the lighting and to avoid follow-up costs.

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Product overview

Street lighting with protection class II luminaire head on a protection class I pole, with or without a second control phase. Should the surge protection be located in the luminaire head or in the pole connection box? There are many possible applications and an equally wide range of suitable surge protection solutions to choose from.

To help you quickly and easily determine the right surge protection and narrow down your selection, we have created the following selection guide for our customers.

MLPC-Series

The products in the MLPC series are designed to protect single-phase powered end devices for protection classes 1 (MLPC1) or 2 (MLPC2). The devices meet the requirements of IEC 61643-11 and VDE 0675 standards and can be used as type 2+3. Various variants enable the best possible customer-oriented solution to be implemented. The MLPC series effectively protects the LED system, even against high-energy surges, and, depending on the version, also protects the dimming (DALI – MLPCH-230L-V/DL, control phase – MLPC1-230L-V/2L).

The diversity of the product range is complemented by further combined variants for optimized energy coordination (MLPC-VGx-230L-x, MLPCHx-230L-x) and additional protection against static charges – ESD (MLPC2-230L-x/ESP2) or temporary overvoltages – TOV / POP (MLPVM2-230L-5A). With its very compact design and a maximum discharge capacity of 10 kA per pole, the MLPC series offers excellent value for money. Connection is via screw terminals (MLPCx-230L-V) or spring-loaded terminals (MLPCx-230L-R). The user can choose between single-sided (MLPCx-230L-x/50) or opposite (MLPC1-230L-x) connection terminals. The housing is mounted in the same way for all versions using standardized mounting holes. This offers the user the necessary flexibility while keeping installation simple.

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MLPM-Series

The MLPM series is a cost-optimized standard series for protecting LED lighting. It effectively protects the LED system with a maximum discharge capacity of 12 kA per pole, even against high-energy surges. The devices meet the requirements of the IEC 61643-11 and VDE 0675 standards and can be used as type 2+3. This is also confirmed by the existing KEMA and ENEC certificates. Versions in protection classes I (MLPM1-230L-R) and II (MLPM2-230L-R) are available. The optical fault signaling on the device is mechanical in nature, so that the protective components can be checked at any time, even without mains voltage. In addition, the ÜSS does not consume any additional energy, as is the case with electronic fault indication via LED. In the event of a fault, the fault message is transmitted indirectly via the circuit separation of the lighting circuit (light is OFF). Connection is made exclusively via spring-loaded terminals. As with all MLPC versions, the MLPM series also features identical, standardized mounting holes, which offer the user the necessary flexibility while maintaining easy installation.

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MLPX-Series

The devices in the MLPX series are type 2+3 surge protection devices designed to protect single-phase end devices, especially for use in LED lighting systems with space constraints. The MLPX devices comply with IEC 61643-11 and VDE 0675 and are available in protection classes I and II. A very compact design, a discharge capacity (Imax) of 10 kA, and a short-circuit resistance of 10,000 A are characteristic of the performance of the MLPX series. Connection is via double-insulated cables, and the fault signaling function allows the operational status to be displayed at any time. In addition, the MLPX offers the option of load circuit separation in the event of a fault, so that an indirect message is also given in the event of a load circuit failure. The devices are available in either IP 67 or IP 20 protection classes.

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MLPCA-Series

The MLPCA series was designed to protect single-phase (MLPCA1-230L) or two-phase (MLPCA1-230-2L) powered end devices for protection class 1 and is specifically used for installation outside a cable transition box. In addition, there are also 2-port versions (2-port MLPCA1-230L-DL and 2-port MLPCA1-230L-2L), which are primarily used in ground-fed bollard lights. The MLPCA series complies with the IEC 61643-11 and VDE 0675 standards and can be used as type 2+3. Thanks to its very compact design and a maximum discharge capacity of 10 kA per pole, the MLPCA series offers a very good performance ratio. The connection is cable-based, with the connection cables housed in a highly flexible and resistant rubber hose cable. The MLPCA arresters offer protection against switching surges from the mains and against earth-bound potential rises.

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Surge protection for DIN rail mounting - DSLP / DLPM / DACN10-Series

The devices in the DSLP, DLPM, and DACN10 series are all compact type 2+3 surge protection devices for DIN rail mounting. Their compact design makes them ideal for use in mast fuse boxes. They comply with IEC 61643-11 and VDE 0675 and are available in protection classes I and II (does not apply to the DACN10 series). The devices have discharge values of up to 15 kA Imax, a low protection level (Up ≤ 1.5 kV), and a short-circuit resistance of 10 kA. Connection is via screw terminals up to 2.5 mm² or elevator terminals up to 10 mm² for the DACN10 series. The fault signaling allows the functionality to be checked at any time. In the DLPM series, this is done mechanically, while in the DSLP and DACN10 series it is indicated electronically via LED. All devices offer the option of load circuit separation in the event of a fault, so that an indirect message is also given in the event of a load circuit failure.

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