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Lightning protection classes

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Lightning protection classes

Introduction

A lightning strike can lead to the destruction of industrial and residential buildings, fire, explosion, failure of transmission lines (PTL), electrical installations and means of information - communication technologies (ICT), and is also dangerous for humans and animals. This force of nature is especially dangerous for the so-called critical infrastructures. Therefore, a range of measures is necessary as a means of protection of objects and structures, both of organizational and scientifically-technical nature. This set of measures received the name - lightning protection. It serves to reduce the risks of exposure to disasters of this kind on industrial and civil infrastructure.

The degree of fire risk (or risk of explosion) of a building or structure depends on the level of severity of the consequences of a lightning strike. In addition, it is necessary to consider the possibility of sparkage in the ceilings, which can be caused by concomitant effects of lightning. For example, the industries that use open flames and combustion processes, usually have fireproof structures. In this case, lightning current flow does not cause a great danger. But if in there are explosives in the workshops, there is an increased risk of life loss and huge material losses. For a specialist it is evident that there is a huge variation of technological conditions for all sorts of buildings, sites and organizations. And in this case, to show the same requirements for lightning protection for all these objects means either to invest extra funds in designing of security systems, or else to accept the inevitability of large risks and damage caused by the negative effects of lightning strikes. In the design of lightning protection systems, you need to take meteorological conditions in the region into account. For example, statistics of thunderstorms in Norilsk will differ from the statistics of thunderstorms in Sochi. Therefore, international regulations prescribe making calculation of risks and potential damage from the effects of lightning to the designers. As a result of these factors, buildings and structures became divided into classes (protection levels), which differ in the severity of possible damage from being struck by lightning. And such a factor, as the activity and lightning storms in the corresponding geographical point, where the object to be protected is located, determines the category of lightning protection.

Legal and regulatory, and technological base of the classification of protected sites

The international practice of the establishment of legal regulatory documents in the field of lightning protection and electrical safety involves the development of the following materials: Technical Regulations (TR), technical codes of established practice (TAP), international standards (IS / IEC) and national standards (GOST), departmental instructions and authorizing documents (AD).

In the field of lightning protection and electrical safety of industrial and civil, the following materials become most frequently used in the design, installation, and certification (categorization):

Classes and levels of lightning protection of buildings and objects of industrial and civil objects

In accordance with the foregoing circumstances, let's analyze the above mentioned regulations for classification and categorization of protected objects.

"Instructions for lightning protection of buildings and structures" (AD 34.21.122-87)

- is the oldest in chronological terms, authorizing document of the USSR times (we will further call it briefly AD). This is a document of direct action, it has an exceptional legal effect, and all organizations were obliged to use it, regardless of their affiliation. Under this guidance, the division of buildings and structures according to their purpose and type of lightning protection systems was carried out in three categories, which were divided into classes of explosive and fire-hazardous zones defined in the EIC, as well as on the type of protection zone, to which a certain reliability is accredited

- 0.995 for zone A and 0.95 for Zone B.

According to AD, the designers were recommended the following measures for lightning protection and grounding I, II, III categories of objects:

1. Protection against direct lightning strikes into buildings and structures that refer to category I (according to AD), is typically implemented using separate rod or catenary wire lightning rods.

Protection of zone A is carried out by means of such lightning rods (see. AD, appendix 3). Elements of lightning rods must be removed from the object to be protected, as well as the underground metal communications. You can choose a natural or artificial ground electrode (see p. 1.8. AD).

Construction of ground electrodes, allowed for separate lightning rods:

  1. a) reinforced concrete pole stub (one or several), its length is not less than 2 m or a reinforced concrete pile (there may be several), its length is not less than 5 m;

  2. b) Reinforced concrete support (diameter of not less than 0.25 m, recessed into the ground not less than to 5 m);

  3. c) reinforced concrete foundation of arbitrary shape (the area of ​​the ground contact is at least 10 m2);

  4. g) artificial ground electrode may consist of a 3 vertical electrodes and more not less than 3 m long, which are united by a horizontal electrode, the distance between the vertical electrodes is not less than 5 m.

Protection against high potential drift is performed in accordance with p. 2.2., 1.8. AD.

  1. 2. Protection against direct lightning strikes of buildings and structures, which refer to category II of lightning protection (according to AD), are usually carried out as follows: freestanding lightning rods or catenary wire lightning rods are installed.

Or they are mounted directly on the protected object. They provide protection area in accordance with the AD (see. Table. 1, p. 2.6 and annex 3.) At the installation of lightning rods on the protected object, there must be at least 2 down conductors from each lightning rod or each pole of catenary wire lightning rod. When the slope of the roof of the building is not more than 1: 8, lightning protection mesh can be used. Installation of lightning rods or imposition of lightning protection mesh is not necessary for buildings with steel trusses, if the conditions under which they are used, are fireproof or nonflammable insulation and waterproofing.

On buildings with metal roof, the itself should be used as a lightning rod.

Down conductors from the metal roofing or lightning protection mesh are laid to the ground electrodes with the distance not less than 25 m along the perimeter of the building.

When soil resistivity is less than 500 ohm * m and the building square is ​​more than 250 sq. m., and also in the ground with the resistivity from 500 to 1000 Ohm * m at the building square ​​more than 900 square meters, a horizontal contour around the building at the depth of 0.5 m is made. In the first case, if the building area is less than 250 meters, and one vertical or horizontal beam-power wave 2-3 meters long is welded to the place of downconductor junstion, while in the second case, of the square is less than 900 sq.m., at least two electrodes are welded.

  1. 3. Protection against direct lightning strikes of buildings and structures, refered to category III, must be performed by one of the methods described in AD (see p.2.11, observing also p. 2.12. and 2.14. of AD), for example using lightning protection mesh. When laying such a mesh, metal structures of buildings are used as down conductors.

Whenever possible, for the objects of category III, it is recommended to use reinforced concrete foundations of the buildings themselves as grounding electrodes to protect against direct lightning strikes. If this is not possible, then artificial ground electrodes are quite applicable. Artificial ground electrode is usually made of two or more vertical electrodes of not less than 3 m long, which are combined by a horizontal electrode not less than 5 m long.

If it is recommended to use as lightning mesh or metal roof as lightning rods, then an exteriour contour, which is made of horizontal electrodes is laid around the perimeter of the building at the depth of at least 0.5 m. In the buildings, the square of which is more than 100 m, the exterior grounding contour can be used for equipotential bonding inside the building (p.1.9. AD). Ground electrode for the protection against direct lightning strikes must be integrated with the ground electrode of the electric installation (p.1.7 EIC).

To protect against the input of high potential along external ground (aboveground) metal communications, it is necessary to connected it to the ground electrode to protect against direct lightning strikes at the input of the building.

"Instructions for lightning protection of buildings, structures and industrial communications" (IS 153-34.21.122-2003)

 - Then IS, the document, which bears the character of a recommendation, which have replaced, but not cancelled the AD, did not make a certainty in the area of ​​classification and categorization of objects of protection from the effects of atmospheric electricity. Firstly, it is not successive with the previous regulatory document - AD, and secondly, the announced reference and guiding materials as annexes to the IS were not released. As a result Rostehnadzor in its explanation about the joint application of AD and IS №10-03-04 / 182 from 01. 12. 2004 allowed joint (combined) use of two instructions that finally confused the already complicated situation with the law-enforcement base in the sphere of lightning protection of buildings and structures for industrial and civil use. So what are the peculiarities of this document? Firstly, in contrast to AD, which stipulated three categories of objects allocated according to their level of protection against lightning impacts, the IS introduces 4 classes of objects according to the parameters of lightning protection systems. Secondly, the regulator proposes to introduce a classifier on the effects of the lightning current. This is done to somehow normalize the means of protection against direct lightning strikes. In general, the standard document is close to the IEC recommendations, but doesn't have full compliance with them, as in its main purpose, the IS determines protection reliability for conventional and special objects, in accordance with the protection level that is set for branch ADs for objects of different types and purposes.

GOST R IEC 62305-1,2,3,4-2010

- a series of IEC documents, already raised to the rank of Russian state standards in the organization of lightning protection systems for industrial and civil buildings. From the work practices, we know that it is impossible to provide absolute protection from lightning. Therefore, technical manuals, which are available in this series of standards, allow to develop effective lightning protection Systems (LPS), providing a significant risk reduction (potential damage) from lightning damage to an acceptable level, and transfer residual risks through the lense of insurance cases. With the help of series of standards it became possible to integrate the entire set of protection measures in the overall system. 2 groups of criteria for the design and application of protection measures were allocated:

  • the set of protective measures that is necessary to reduce the level of damage to the facilities, as well as to reduce the risk of threats to the lives of personnel in the building, forms the first group (IEC 62305-3);
  • the set of protective measures that are required to reduce the number of electrical circuits breakdown, which are located in the structures, form the second group (IEC 62305-4).

Only by taking into account all the parameters of the protected object, the designer selects the appropriate levels of lightning protection.

In this series of standards there are 4 LP classes (I - IV) and protection levels are fixed in accordance with them (see. IEC 62305-1, Table. 1).

Any class can be described by certain parameters that are considered either dependent on the lightning protection level or independent:

Parameters that depend on the class of lightning protection:

  • parameters describing lightning (see. IEC 62305-1, Table. 3,4,5);
  • rolling sphere (its R is taken), cell (its size is taken), protection angle value (see. IEC 62305-3, item 5.2.2);
  • the distance between the collectors (typical), the distances between the annular conductors (see IEC 62305-3, p. 5.3.3);
  • distances from dangerous arcing places, which can be considered nonhazardous (see IEC 62305-3, p. 6.3);
  • ground electrodes' length (the minimum value is taken), (see IEC 62305-3, p.5.4.2).

Parameters that do not depend on lightning protection class:

  1. the value of equalization of lightning potentials (see IEC 62305-3, p. 6.2);
  2. the measured thickness of the metal sheets (minimum value), and the metal pipes located in the lightning rods (see IEC 62305-3, item 5.2.5);
  3. LP materials, conditions of use of these materials (see IEC 62305-3, p. 5.5);
  4. parameters of lightning rods (material from which they are made, minimum sizes, configuration). Here we consider down conductors and ground electrodes (see IEC 62305-3, p. 5.6).

Let us stop at this point in more detail, since its treatment in the different regulations has some differential peculiarities.

When considering spreading of high-frequency lightning current into the ground, and in order to minimize any dangerous overvoltages, the configuration and size of the grounding system are important criteria. As a rule, low grounding resistance is recommended (if possible less than 10 ohms, measured at a low frequency). For lightning protection, it is preferable to use a separate ground electrode built into structure and suitable for all the purposes (for example, for lightning protection, power and communication systems).

Grounding systems must be connected in accordance with IEC 62305-3, para. 6.2. Two main structural types for placing ground electrodes are used (A and B).

Placement of type A: This type of placement includes horizontal or vertical electrodes installed outside the building to be protected and connected to each down conductor. The total number of ground electrodes used in Type A placement, should be at least two.

Placement of Type B: This type of placement includes either an annular conductor located outside the protected building, being in contact with the soil to 80% of its total length, or a ground electrode in the foundation. These ground electrodes may also be mesh. Type B grounding placement is recommended for buildings with electronic systems, as it can reduce the effect of noise pickups and surges. Ground electrode parameters are defined in IEC 62305-3, p. 5.4.2.2.

However, based on the total comprehensive analysis of the existing regulations, it is possible to make a conditional classification of lightning protection objects according to lightning protection levels.

Object of I class of lightning protection

Object: special (crucial), dangerous for the environment, human and animal life activity. Object type: chemical and petrochemical production, biochemical and bacteriological enterprises, production of explosives, nuclear power plants and others.

Guaranteed reliability of protection against direct lightning strikes- 0.98 (higher level of 0.995 may be set for a separate category of A zone objects). Adverse consequences arising from a lightning strike: fire, explosion, toxic emissions, increased radiation on a large area and so forth. The extreme case - an ecological disaster with irreparable material and human losses.

Object of the II class of lightning protection

Here we describe types of special objects that represent danger to the immediate environment.

Object type: oil refining, gas station, milling, woodworking factories, production of plastic products and so on.

Guaranteed reliability of protection against direct lightning strikes- 0.95 (a higher level may be set for a separate category of B zone objects).

Adverse consequences arising from a lightning strike: fires, explosions inside the building and the adjacent territory. Probable collateral damage of walls and ceilings, as well as severe injuries and even death of employees and visitors. In this case, significant losses are recorded.

Object of the III class of lightning protection

Object: special, crucial infrastructure.

Object type: communication and ICT enterprise, pipeline transport, power transmission lines, central heating equipment, transport infrastructure and others.

Guaranteed reliable protection against direct lightning strike - 0.9.

Adverse consequences arising from a lightning strike: interruption of communication, partial or complete loss of control, interruptions in water supply and heating, temporary reduction in quality of life and material losses.

Object of the IV class of lightning protection

Object: general, industrial and civil buildings and related infrastructure.

Object type: residential buildings, industrial facilities (not higher than 60 m.), homes and cottages in the villages, social and cultural facilities, educational institutions, hospitals, museums, temples, churches and others.

Guaranteed reliable protection against direct lightning strike - 0.8. Adverse consequences arising from a lightning strike: strong fire, damage to buildings, transport disruption, interruption of communications systems, possible loss of historical and cultural heritage. Significant material and financial losses. There can be human losses. As shown in the classification system, any class of lightning protection has characteristic differences (designation) from another class of the object and parameters of lightning protection, as well as the type of the grounding device, the design of which is determined by the purpose and location of the structure.

Conclusion

Having considered the problems of lightning protection of industrial and civil facilities and infrastructure in this analytical review, it can be stated that the issues of protection from the effects of atmospheric electricity, in terms of regulation and application of the legal normative and technical base in the Russian Federation are determined by quite a wide range of existing regulations, namely IS, AD, GOSTs and so forth. Using a combination of the document provisions will help to build a complete lightning protection system for objects of all classes and categories.  We can distinguish two approaches to the design of lightning protection. The first - construction of lightning protection in accordance with the AD categories. The second - provision of the required reliability of protection, guided by the IS and industry standards. Selection of the regulatory documents depends on the sphere, where the design is carried out and on filling of the domain by the internal documents. In general, industry standards contain updated requirements of the IS and AD, so that we can say that these documents remain to be determining due to the long-term traditional experience of their use. GOSTS and IEC standards are used as reference, and they are engaged in case of incompleteness or absence of certain parameters of lightning protection in AD or IS.

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