Keeping Telecommunications Online With Surge Protection

Lightning and surge protection is indispensable for protecting human lives, preventing fires, and avoiding costly outages of networked systems. Dehn had been Webb’s partner of choice for the last five years when it comes to protection. Webb supplies Dehn products to protect equipment against AC/DC surges and lightning.

DEHNvap

A recent addition to the product portfolio, DEHNvap is a modular prewired combined arrestor and protects cellular sites’ 230/400 V power supplies. TN-C, TN-S and TT systems can use it universally. The design is optimised for mobile communication applications. When using combined arrestors, energy coordination with system and equipment technology is an important criterion. For this reason, Dehn has extensively tested DEHNvap in their test laboratory to ensure its coordination with the integrated input circuits of power supply units.

The DEHNvap range includes:

• DEHNvap CSP 1P 50 S FM: A prewired combined arrestor, energy-coordinated with power supply systems for cell sites in a new compact two standard DIN module design.
• DEHNvap CSP 3P 100 S FM: A prewired combined arrestor, energy-coordinated with power supply systems for cell sites in a new compact four standard DIN module design.
• DEHNvap CSP 1P 255 FM: A plug-in, prewired combined arrestor, energy-coordinated with power supply systems for cell sites in a two standard DIN module design.
• DEHNvap CSP 3P 100 FM: A plug-in, prewired combined arrestor, energy-coordinated with power supply systems for cell sites in an eight standard DIN module design.

How lightning causes damage

Once one understands how lightning causes damage, the need for surge protection becomes apparent. There are different causes of lightning damage; therefore, protection techniques may vary and require the deployment of more than one protection device to protect all items.

When evaluating a building or structure, one should consider the structure itself and all incoming cables; that is, equipment signal cables and power cables. This evaluation leads to the identification of the four possible sources of damage:

1. A lightning strike directly to the building;
2. A lightning strike near the building;
3. A lightning strike directly to an incoming line; and
4. A lightning strike near an incoming line.

Nearby strikes cause surges: in striking neighbouring buildings, surrounding objects or areas close to incoming lines, the generated lightning current casts a magnetic field over the structure or lines. This magnetic field generates an induced current on the incoming line or cables inside the structure. Surge protection devices (SPDs) reduce the induced effects of lightning. Lightning rods, also known as external lightning protection, prevent burning or mechanical damage.

Protection installations

Installing external protection protects against structural damage but will not necessarily prevent electronic equipment from being damaged (for example, TVs, Internet routers and appliances such as kettles, fridges and microwaves). Therefore, to protect equipment, surge protection devices are also needed.

To evaluate the risks, the following parameters from the SANS 62305-2 standard are relevant:

• For direct strikes, consider an area around the structure with a radius of three times the structure’s height.
• For surges, consider an area around the structure with a radius of 500 metres. Bear in mind that strikes up to two kilometres away in both directions can generate surges on incoming lines.

The risk of surges occurring, therefore, exceeds the risk of direct lightning strikes. Correct installation of surge protection devices is consequently essential.

Surge arrestors also minimise damage caused by switching surges coming from the grid, an occurrence that is particularly relevant given the incidence of load shedding in South Africa.

About DEHN

Over the years, DEHN developed numerous market-leading surge arrestors, with the latest offering being the new DEHNguard ACI surge protection device. This surge arrestor uses ACI technology and 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 and optimally adjusted for the arrestor. A connection cross-section of just 6 square millimetres facilitates 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 much better TOV withstanding characteristics.

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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