In order to understand the need for surge protection, it is important to understand how lightning causes damage. The sources of lightning damage can be quite different, therefore different protection techniques may be required to protect different items.
There are two areas of concern when evaluating a building or structure, namely the structure itself, and all incoming cables, meaning IT equipment as well as power. From this, the four sources of damage are derived, as per the following possibilities:
• Having a lightning strike directly to the building.
• A strike near the building.
• A strike directly to an incoming line.
• A strike near the incoming line.
Nearby strikes cause surges: in striking neighbouring buildings, surrounding objects or areas next to incoming lines, the lightning current coming down generates a magnetic field, which is cast over the structure or lines. This magnetic field generates an induced current on the incoming line, or on cables inside the structure. To prevent resulting damage to electrical equipment, surge protective devices (SPD) are recommended to reduce the induced effects of lightning. To prevent burning or mechanical damage, lightning rods are installed, also known as external lightning protection.
By installing external protection, users protect against structural damage, but this will not necessarily prevent electronic equipment from being damaged (for example TVs, Internet routers and appliances such as kettles, fridges, microwaves and so on). Therefore, in order to protect equipment, surge protective devices are needed as well.
The calculation from the SANS 62305-2 standard to evaluate the risks are as follows:
• The area to be considered for direct strikes is a radius around the structure, which is three times the height of the structure.
• The area to be considered for surges is a radius of 500 metres around the structure, and can be up to two kilometres away in both directions for incoming lines.
The risk of resultant surges therefore exceeds that of direct lightning strikes, meaning that the correct installation of surge protection devices is extremely important. Other benefits of surge arresters include the minimising of switching surges coming from the grid. This is a relevant topic when seen against the background of recent load shedding from the South African grid.
Over the years, DEHN has developed numerous market-leading surge arresters, with the latest offering being the new DEHNguard ACI surge protective device. This surge arrestor with ACI technology allows users to save space, time and costs. It is a prewired, unit that consists of a base part and plug-in protection modules. Its benefits include:
• Safe dimensioning and the elimination of mistakes: The new switch/spark gap combination is integrated directly into, and ideally adjusted to, the arrestor. A connection cross-section of just 6 square millimetres makes for easier installation and saves time that otherwise needs to be spent dimensioning the cross-section.
• Being able to withstand temporary over-voltages (TOV) increases system availability and saves on maintenance and repair costs. TOV caused, for example, by loss of neutral, can destroy conventional surge protective devices. The new ACI arrestors have a much better TOV withstand.
• Zero leakage current increases the service lifetime of arrestors. ACI arrestors also avert the accidental tripping of the insulation monitoring and contribute towards operational safety.
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