Lightning poses a clear threat to a structure but a growing. Structural lightning protection can no longer be in. The use of enhanced SPDs provides a practical. This A4.
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Furthermore, It defines the relationships between damage and loss that form the basis for the risk assessment calculations in part 2 of the standard.
Lightning current parameters are defined. These are used as the basis for the selection and implementation of the appropriate protection measures detailed in parts 3 and 4 of the standard. Part 1 of the standard also introduces new concepts for consideration when preparing a lightning protection scheme, such as Lightning Protection Zones LPZs and separation distance. The relationships of all of the above parameters are This in essence would prevent the penetration of the summarised in Table 5.
However, in practice it is not possible or indeed cost For a more detailed explanation of the general effective to go to such lengths. This reduction in damage and IEC equivalent. Please see page for more details consequential loss is valid provided the lightning strike about this guide. Each level has a fixed Minimum 3 5 10 16 set of maximum and minimum lightning current current kA parameters.
The assessment and management of risk is now significantly more in depth and extensive than the approach of BS The ultimate aim of the risk assessment is to quantify and if necessary reduce the relevant primary risks i. Each primary risk Rn is determined through a long NO series of calculations as defined within the standard.
The above process is repeated using new values that relate to the chosen protection measures until Rn is less than or equal to its corresponding RT. StrikeRisk risk management software An invaluable tool for those involved in undertaking the complex risk assessment calculations required by BS EN , StrikeRisk facilitates the assessment of risk of loss due to lightning strikes and transient overvoltages caused by lightning. Contact Furse for more details about StrikeRisk. These LPLs equate potential damage.
Therefore it is vitally important to use a I I correctly designed air termination system. Depending upon positioning requirements laid down in the body of the the consequences the designer may choose either of standard. It highlights that the air termination the following types of external LPS: components should be installed on corners, exposed l Isolated points and edges of the structure.
The basic concept of applying the rolling angle sphere to a structure is illustrated in Figure Furthermore the new standard uses the height of the air termination system above the reference plane, whether that be ground or roof level The rolling sphere method was used in BS , the See Figure The protective angle method is suitable for simple shaped buildings. However this method is only valid up to a height equal to the rolling sphere radius of the The protective angle method appropriate LPL.
The protective angle method is a mathematical simplification of the rolling sphere method. The protective angle a is the angle created between the 1 tip A of the vertical rod and a line projected down to h1 2 the surface on which the rod sits see Figure The protective angle differs with varying height of the air rod and class of LPS.
The outcome was to remain with the information housed within this standard. Natural components So on all structures particularly with flat roofs, When metallic roofs are being considered as a natural perimeter conductors should be installed as close to air termination arrangement, then BS gave the outer edges of the roof as is practicable.
Vertical air puncture, hot spot or ignition problems. The air rods should be spaced not more than 10 m apart and if strike plates are used as an alternative, these should be strategically placed over the roof area not more than 5 m apart. The greater the number of down conductors the better the lightning current is shared between them. This is enhanced further by equipotential bonding to the conductive parts of the structure.
Lateral connections sometimes referred to as coronal bands or ring conductors provided either by fortuitous metalwork or external conductors at regular intervals are also encouraged. The down conductor spacing should correspond with the relevant class of LPS see Table Down conductors should wherever possible be installed at each exposed corner of the structure as Stranded copper cable research has shown these to carry the major part of the 70 mm2 PVC insulated lightning current.
Additionally, it states that reinforcing bars are welded, clamped with suitable connection components or overlapped a minimum of 20 Bonding conductor times the rebar diameter. This is to ensure that those reinforcing bars likely to carry lightning currents have Figure Typical methods of bonding to steel reinforcement secure connections from one length to the next.
If the connection from the dedicated copper conductor from the top of the bonding conductor to the rebar is to be encased in structure to the foundation prior to the pouring of the concrete then the standard recommends that two concrete.
The joints periodically. For new build structures this the structure. It dispersion of lightning current safely and effectively comprises conductors that are installed in the concrete into the ground. If any additional lengths In line with BS , the new standard recommends a of electrodes are required they need to meet the same single integrated earth termination system for a criteria as those for type B arrangement. Foundation structure, combining lightning protection, power and earth electrodes can be used to augment the steel telecommunication systems.
The agreement of the reinforcing foundation mesh. A good earth connection should possess the following characteristics: l Low electrical resistance between the electrode and the earth. The lower the earth electrode resistance the more likely the lightning current will choose to flow down that path in preference to any other, allowing the current to be conducted safely to and dissipated in the earth l Good corrosion resistance. The choice of material for the earth electrode and its connections is of vital importance.
It will be buried in soil for many years so has to be totally dependable The standard advocates a low earthing resistance A sample of Furse high quality earthing components.
Separation isolation distance of Three basic earth electrode arrangements are used. This will minimise any chance of partial lightning current being introduced internally in the structure.
Type A arrangement This can be achieved by placing lightning conductors This consists of horizontal or vertical earth electrodes, sufficiently far away from any conductive parts that connected to each down conductor fixed on the have routes leading into the structure.
So, if the outside of the structure. This could be due, with bonding conductors is not suitable. The gas, water and central over to internal metallic installations. The power cable is insulation distance between the metallic parts can bonded via a suitable SPD, upstream from the electric avoid dangerous sparking between different meter, to the equipotential bonding bar. This bonding metallic parts. In Lightning equipotential bonding larger or extended structures several bonding bars may Equipotential bonding is simply the electrical be required but they should all be interconnected with interconnection of all appropriate metallic each other.
If the routed into the structure should also be bonded at the metallic parts are essentially at the same potential then equipotential bar. As a society, we are now heavily reliant on the continuous and efficient running of such systems.
The use of computers, electronic process controls and telecommunications has exploded during the last two decades. Not only are there more systems in existence, the physical size of the electronics involved has reduced considerably smaller size means less energy required to damage circuits. LEMP is the term given to the overall electromagnetic effects of lightning, including conducted surges transient overvoltages and currents and radiated electromagnetic field effects.
LEMP damage is so prevalent such that it is identified as one of the specific types D3 to be protected against and that LEMP damage can occur from ALL strike points to the structure or connected services - direct or indirect - for further reference to the types of damage caused by lightning see Table 5 on page This extended approach also takes into conductor creates a magnetic field in which energy is account the danger of fire or explosion associated with stored.
When the current is interrupted or switched services connected to the structure, e. In an attempt to dissipate itself it becomes a high voltage transient. Lightning is not the only threat… The more stored energy, the larger the resulting transient. Higher currents and longer lengths of Transient overvoltages caused by electrical switching conductor both contribute to more energy stored events are very common and can be a source of and also released!
Current flowing through a This is why inductive loads such as motors, transformers and electrical drives are all common causes of switching transients.
As a result protection was often fitted after equipment damage was suffered, often through obligation to insurance companies. This in itself is a significant deviation from that of BS Such SPDs are required to protect against reduction in LEMP severity, from conducted surge the risk of loss of human life by preventing currents and transient overvoltages, as well as radiated dangerous sparking that could present fire or electric magnetic field effects.
Designers coordinate these shock hazards. Lightning current SPDs form one part of a coordinated External zones set of SPDs that include overvoltage SPDs - which are LPZ 0A is the area subject to direct lightning strokes needed in total to effectively protect sensitive and therefore may have to carry up to the full electrical and electronic systems from both lightning lightning current.
This is typically the roof area of a structure. The full electromagnetic field occurs here. Figure 22 illustrates the basic surges can occur here. Internal zones LPZ 1 is the internal area that is subject to partial Boundary Antenna lightning currents. Equipment Critical This is typically a screened room or, for mains power, at equipment the sub-distribution board area. Protection levels within a zone must be coordinated Equipment B with the immunity characteristics of the equipment to be protected, i.
Water pipe B line The existing fabric and layout of a building may make Gas pipe readily apparent zones, or LPZ techniques may have to be applied to create the required zones. However it is the correct installation of coordinated Surge Protective Devices SPDs that protect equipment wherever services from damage as well as ensuring continuity of its operation - critical for eliminating downtime.
When applying bonding, shielding and SPDs, technical to another excellence must be balanced with economic necessity. For new builds, bonding and screening measures can be integrally designed to form part of the complete Poor coordination could mean that the overvoltage SPM. However, for an existing structure, retrofitting a SPDs are subject to too much surge energy putting set of coordinated SPDs is likely to be the easiest and both itself and potentially equipment at risk from most cost-effective solution.
Furthermore, voltage protection levels or let-through voltages of installed SPDs must be coordinated with the insulating withstand voltage of the parts of the installation and the immunity withstand voltage of electronic equipment. Enhanced SPDs Whilst outright damage to equipment is not desirable, the need to minimize downtime as a result of loss of operation or malfunction of equipment can also be critical.
This simply means a series of SPDs whose effective protection against outright damage but not locations and LEMP handling attributes are against downtime due to system disruption. Appropriate SPDs should be fitted wherever common mode and differential mode between live services cross from one LPZ to another.
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