Lightning protection - Getting the right surge protection

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The extensive use of electronics within industrial processes and buildings has meant  protection against the effects of voltage surges is no longer an option but has become a necessity. Lightning produces an extremely large quantity of pulsed electrical energy, which means surge protection devices designed to limit transient overvoltages need to be correctly specified to ensure they are effective. Tom France from Schneider Electric looks at the selection considerations, taking into account location and the types available

As business operations become increasingly sophisticated, the use of technologies such as LCD screens, computer networks, data servers and industrial equipment such as programmable logic controllers, means that protection against the effects of voltage surges is crucial.

When it comes to lightning protection, safety is a major concern as is preventing expensive equipment from being damaged. A surge protection device (SPD) is a component of the electrical installation protection system. It is typically connected to power cables entering and leaving the building at the main switchboard. However, depending on the design of the electric scheme, SPDs can also be positioned elsewhere. For example, if the business has air conditioning units on the roof, then it will be vital to include a protection device on the cables to or from the units.

Lighting protection may sound like an exaggerated requirement, but every year the earth is struck by around three billion strokes of lightning, potentially causing fires and posing a risk to buildings and equipment. This can be a significant loss to any business, not only through the repair itself, but also as a result of subsequent downtime.

SPDs are designed to limit transient overvoltages caused by lighting and diverting them to earth to avoid causing damage. To ensure they are effective though, it is important to recognise there are three different styles of device available.  ‘Type 1' only protects an electrical installation from a direct lightning strike to overhead power lines, while ‘Type 2 and 3' safeguard electrical equipment from the indirect effects of lightning or overvoltages from within the electrical system. This can include storms that are some distance away, but still have the potential to damage a power line and consequently affect electricity supplies.

To ensure the correct protection device is selected there are three stages that need to be followed, addressing the individual needs of the project. The first step is to estimate the value of the equipment that needs to be protected, for both the cost of it and the economic impact should it fail. This inevitably covers not only large electrical items such as automated heating systems and lifts, but also professional equipment, including computers and servers.

The second step in the specification process is to identify the electrical architecture of the building. Dependant on the size of the premises and the extent of its electrical system, more than one surge protector may be required. The type of SPD to be installed close to the start of the electrical circuit depends on whether or not a lightning protection system is present. If there is a lighting rod for example, on the building or within 50 metres of the building, then Type 1 should be fitted. Then the number of SPDs to be installed is determined by the size of the site and the difficulty of installing bonding conductors. On large sites with long cable runs, it is vital to install a SPD at the incoming end of each sub distribution enclosure.
The final stage is to determine the risk of the impact of lightning on the site. Different locations will have varying levels of threat, for example, an urban, low-lying area will be less at risk than a site with a particular hazard such as a pylon, a tree or a high structure.

Looking at these three different aspects of an installation will ensure the right type and number of protection devices will be used. Many manufacturers of surge protectors, including Schneider Electric, will also be able to assist in the specification process for those who are not confident in selecting the best option. In addition, manufacturers have introduced solutions combining Type 1 and 2 for full protection and can provide full information on the correct overcurrent protection device needed for the SPD.

Lightning can produce extremely large quantities of pulsed electrical energy. But installing the correct lightning protection device means any building can benefit from increased levels of protection, reducing the risk of extensive damage to the electrical system and equipment. Installing a SPD is relatively simple and an added benefit is that the equipment can be retrofitted, making it a viable option for all businesses.

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