Feature Surge Protection
Direct and indirect lightning strikes will put the electrical/ electronic contents of a structure at risk. Here, DEHN offer some advice on how to correctly manage these dangers
ritish Standard BS EN 62305 superseded BS 6651 in August 2008 and became the UK’s national standard for lightning protection. The standard consists of four separate documents, each section dealing with different aspects of light- ning and protection:
BS EN 62305-1 General Principles. BS EN 62305-2 Risk Management. BS EN 62305-3 Physical Damage to Structures and Life Hazard. BS EN 62305-4 Electrical and Electronic Systems.
Once the General Principles and structure of the standard is understood it can be seen that by applying a logi- cal approach, a fully coordinated system of protection for both struc- tures and electronics can be achieved.
An insight into protection B
Equipment located in LPZ0A . Damages and dangers Step one
The first step in the process is to define the risks to be considered: R1: Risk of loss of human life. R2: Risk of loss of service to the public. R3: Risk of loss of cultural heritage. R4: Risk of loss of economic value. By working through a series of for- mulae the actual risks can be quanti- fied. These are then compared with the tolerable risk values contained within the standard.
The calculated risk (R) is compared with the tolerable risk (RT
) to deter-
mine if a problem exists with the spe- cific risk being considered. R < RT R > RT
- No problem - Potential problem
Should a potential problem exist remedial action may be required. Dependant upon the type of risk being considered, this may require either a class of external LPS to be fitted or internal lightning current or surge arresters to meet the require- ment of a specific lightning protec- tion level (LPL), or a combination of both plus other methods.
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BS EN 62305-3 Physical Damage to Structures and Life Hazard includes: a) External Lightning Protection System (LPS), consisting of an air ter- mination system, down conductors and earth termination system. b) An LPS to prevent dangerous sparking using either equipotential bonding or separation distance. c) The basic design parameters based on the lightning protection level (LPL). BS EN 62305-4 Electrical and Electronic Systems. The -4 document is dedicated to the problems encoun- tered due to lightning current and induced surges, and it includes: a) Direct strike, lightning current and surge protection. b) Indirect strike induced surge voltages. c) Earthing and bonding. d) Magnetic shielding and line routing. e) The basic design parameters based on the LPL.
Lightning protection zone concept Using the protection principles out- lined in BS EN 62305-4 the protec- tion of electrical and electronic systems against induced lightning current and voltage surges is based on the principle of lightning protec- tion zones (LPZs).
The structure being protected is divided into zones subject to the location of the equipment within the structure. Using this principle, suit- able zones can be defined according to the number, type, immunity and sensitivity of the electrical and elec- tronic devices or systems present within the structure. LPZ0A
- Systems in external areas, but protected against direct lightning strikes - partial lightning current. LPZ1
- Systems in unprotected external areas of structure - direct lightning current. LPZ0B
- Systems in normal operational
areas. LPZ2
- Systems in safety relevant JUNE 2013 Electrical Engineering . At the boundaries of LPZ1/2
operational areas such as control or server room, etc.
The principle being to attenuate either the lightning current or surge voltage to a lower controlled level at each zonal interface.
may be
subject to direct lightning strikes, with currents up to 200kA 10/350µS wave- shape. Based on providing external lightning protection utilising either the rolling sphere principle or angle of protection, partial lightning currents may be present in LPZ0B
The diagram below shows that a lightning current arrester, SPD Type I, (Waveform 10/350) is required at the interface of zones LPZ0/1
for any con-
ductive cable entering from a zone LPZ0A
and
higher, a surge arrester SPD Type II (Waveform 8/20) would be used.
Protection management To achieve a high level of safety for people and equipment it is essential that there is close co-ordination on all aspects of the work between the build- ing experts e.g. civil and electrical engineers, lightning protection design- ers and installers and the surge protec- tion experts with an appropriate management plan being adhered to. DEHN (UK) can help at all stages of the project. The initial risk assessment can be carried out by using DEHN’s software - DEHNSupport. Full techni- cal, practical and application advice on all aspects of the standard are avail- able from the technical department, and once designed, DEHN is equipped to supply all materials required to complete the project.
DEHN also offer a full day seminar based around BS EN 62305, covering the major points within the standard and how to practically apply them to live situations.
DEHN
www.dehn.co.uk T: 01484 859 111
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