CABLEtalk

Surviving The Shock

The extensive use of electronics within industrial processes
and buildings has meant protection against voltage surges isn’t just an option - it’s a necessity. Lightning produces an enormous quantity of pulsed electrical energy. This means surge protection devices, designed to limit transient overvoltages, need to be exactly specified to ensure they are effective. Tom France from Schneider Electric looks at the selection considerations, taking into account location and the types available.

 

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

 

When it comes to lightning protection, safety of employees and of equipment is paramount. Wherever possible businesses will want to prevent expensive technical 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 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.PB104264-35

 

As I look out my window to bright blue skies, lightning protection may sound like an exaggerated requirement. However every year the earth is struck by around three billion bolts of lightning. These strikes cause fires and pose a significant risk to buildings and equipment. This can create a substantial loss for any business, not only through the repair itself, but also as a result of the inevitable downtime.

 

SPDs are designed to limit transient overvoltages caused by lightning and divert them to earth to avoid causing damage. Whilst they all have the same goal, it is important to note there are three different styles 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 to address the individual needs of each project.

 

The first step is to estimate the value of the equipment that needs to be protected. This has to encompass both the cost of replacement 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 and loss of data.

 

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 lightning 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. In addition several manufacturers have introduced solutions that combine Type 1 and 2 for full protection. They can provide full information on the correct overcurrent disconnection device needed for the SPD.

 

Surge protection devices can be supplied either as a fixed unit or with interchangeable cartridges. They can also have varying performance levels so the correct choice of overcurrent disconnection device should be coordinated within the system.

 

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.