Protection of LED lights against overvoltage

Overvoltage causes, experiences and protection concepts

The trend towards LED lighting in interior and exterior lighting is steadily increasing. to. In the meantime, many local authorities and network operators throughout Europe have experience with this relatively new technology. It seems that the advantages, especially in terms of energy savings and intelligent lighting control, will ensure that the share of LED solutions in lighting technology will continue to rise steadily in the future. In street lighting, this is already evident in many cities, but the trend is also on the rise in industrial and building lighting. However, here too it is clear that there are both light and shade sides.

In recent years, it has become apparent that overvoltages in particular represent a serious problem for sensitive electronics. Initial feedback from the field confirms this. The city of Esbjerg, for example, reported the largest failure to date of over 400 street lights as a result of a lightning strike. This is particularly worth mentioning as Denmark is one of the lightning poorest regions in Europe.

Lightning strikes can reach very high values depending on the distance of the impact location, the ground and earthing conditions and the flash intensity. Fig. 1 shows the qualitative influence on the light points of street lighting caused by the formation of a potential funnel at a lightning strike.

During switching operations in the network, voltage peaks of several thousand volts are generated, which propagate in the low-voltage network and load other equipment.

A typical example 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 charges are a phenomenon which occurs particularly in the case of Protection class II Luminaires where charge separation occurs (Fig. 3) and then a high voltage on the luminaire housing or heat sink of the LED. This phenomenon is a real challenge for every car driver. who, when he grips his car, can sometimes get an electric shock got.

Particularly affected are luminaires which are operated completely isolated from earth potential. will be. Examples are SK II luminaires on plastic masts or cable suspensions. By using the 'MLPC2-230L-V/ESP' protective device, the following can be achieved these static charges and consequential damages are prevented.

Mains faults can lead to so-called temporary overvoltages. The drop in the neutral conductor, e.g. due to damage, is the most frequent cause here. With this fault, the nominal voltage can increase up to 400 V on the phases due to mains asymmetries in the 3-phase mains (Fig. 4). The protection against temporary overvoltages requires special consideration. Citel offers special devices of the PSPD and VM series.

But there are also problems in building and hall lighting. In particular where overvoltages do not originate from outside, but daily from the own plant. In particular, cases are known from the industry, in which which generate overvoltages in electrical equipment and which are caused by the electrical wiring reaches the lighting. First sporadic failures individual luminaires or LEDs are the typical signs of this.

State of the art

Based on this experience, too, luminaire manufacturers have met their requirements for to the strength of the luminaires against overvoltages. Lag the strength of street luminaires against overvoltages several years ago. at approx. 2,000 - 4,000 V, it currently averages approx. 4,000 - 6,000 V.

However, this is often not enough, as can be seen from image 5.

This experience has also prompted luminaire manufacturers to raise their requirements for luminaire strength against surge voltages. Whereas a few years ago the strength of street luminaires against overvoltages was approx. 2,000 - 4,000 V, it is currently approx. 4,000 - 6,000 V on average.

Protection concepts

In order to take this into account, many luminaire manufacturers offer the option of Luminaires with a powerful Type 2+3 surge protection device (SPD) to protect the world. If this is not possible or intentional, e.g. due to lack of space or because the luminaires are already installed in the field, the SPD can also be installed in the mast fuse box. can be used. This also offers the advantage of the simpler Maintenance and retrofitting. To complete the protection concept and relieve the light points. (Fig. 6) should additionally be equipped with a combined arrester type 1+2+3 in the street switchgear/Central distributor against the propagation of lightning currents and overvoltages be protected.

In building services engineering (Fig. 7), effective protection can be achieved by equipping the electrical installation with lightning and surge protection devices. For example, combined lightning and surge arresters type 1+2+3 can be used for protection against lightning currents and mains transients in building feed-in systems, and SPD type 2+3 light distribution boxes and junction boxes for luminaires can be used for protection against field couplings and switching overvoltages.

Practical overvoltage protection

There are many manufacturers for surge protection on the market. Therefore should be based on the following points when selecting surge protection devices be paid special attention to.

1. A good overvoltage protection should be tested according to IEC 61643-11 and the requirements of VDE 0100-534. In order to achieve this, the following requirements are among others met Status signalling and disconnecting devices are integrated in the SPD.
2. Since the SPD is usually concealed at inaccessible points, e.g. in luminaires is installed, pure optical signalling is not ideal. An SPD that can also disconnect the luminaire from the circuit in the event of a fault, the following features are available here a good and simple way of indirect signalling.
3. The size and type of mounting of the SPD must meet the requirements of the installation site. correspond.
4. If moisture or dust occurs, an SPD with elevated IP class should be selected.
5. SPDs must take into account the protection class (SKI or SKII) of the luminaires.
6. In addition to the protection for the 230 V supply, the protection of the controller should also be taken into account, such as DALI, second (control) phase, 1 - 10 V or DMX. SPDs, which combine AC and control, are ideal for these luminaires and usually offer better coordinated protection than two individual SPDs.

Conclusion

LED technology is becoming increasingly important in lighting. Further development technology ensures ever more reliable solutions. Practice-oriented, adapted Overvoltage arresters and protection concepts (Figs. 6 and 7) fuse the sensitive electronics from harmful overvoltages. The additional Costs of an effective overvoltage protection concept for a luminaire system currently account for less than one percent of total costs. Overvoltage protection measures are therefore a must for every plant operator. simple and in many cases indispensable means of ensuring the long service life of the and reliability of the lighting and to avoid consequential costs.

Download technical paper - Standard-compliant surge protection for modern LED street lighting