Irrespective of the fuel type used in the boiler, during the operation, combustion products are formed which are vented using the chimneys. According to SNiP II-35-76 Construction Standards and Rules. Boiler Stations, "the chimney height should be greater than the wind leg edge and at least 2 m over the roof in the higher part of the building or the highest building within a 10 m radius. Brick chimneys are 30 to 70 m high; reinforced chimneys are up to 300 m, and steel ones are over 40 m. Due to such heights, the chimneys often get lightning strikes, therefore the boiler should be equipped with a lightning protection system.
Guidelines for Arrangement of Lightning Protection of Buildings, Structures, and Industrial Utilities (SO 153-34.21.122-2003; hereinafter, SO) classifies boilers as conventional structures in terms of lightning protection which implies additional effects depending on the production conditions, and minor to significant damage in case of a lightning strike. According to Guidelines for Arrangement of Lightning Protection of Buildings and Structures (RD 34.21.122-87, hereinafter, RD), the boiler is classified to Category III and should be protected from direct lightning strikes.
Protection of buildings against lightning strikes is provided by using lightning arresters. Lightning arrester is a device that is elevated over the protected facility through which the lightning current goes into the ground bypassing the protected facility. It consists of a lightning rod that accepts the lightning discharge directly, a current collector, and a grounding electrode.
Protection zone of a repeated lightning arrester is defined as a protection zone of pairs of adjacent lightning arresters of h ≤ 150 m (see items 2.1, 2.2 hereof).
The set of arrangements ensuring compliance with the lightning protection requirements is based on the following solutions:
- 5 x 1.5 lightning rods are installed on the boiler chimneys. It is considered that 0.5 m of the rod length is used for securing;
- current collectors are laid from the lightning rods down along the chimneys which are secured using clamps GL-11703A (spacing 0.6-1 m);
- on the building, installation of 3 x 7 m lightning rods is carried out by attachment to the wall. It is taken into account that 1.5 m of the height of lightning rod is necessary for mounting;
- Lightning rods are interconnected to arrange two current collectors using galvanized steel wire D = 8 mm from each lightning rod. Current collectors are attached (with mounting step 0.6-1 m):
- on the roof using clamps GL-11747A;
- to the walls using clamps GL-11703A;
- connection and branching of current collectors are made using clamps GL-11551A.
RD 34.21.122-87. Appendix 3. Lightning arrester protection zones
Protection zone (in plan view) of a repeated lightning arrester
I is the protection zone edge at the level hx, 2 is the same at the ground level
A set of activities to provide the necessary requirements to the grounding arrangement conforms to item 2.26 of RD 34.21.122-87 and is provided by the following solutions:
- mounting of a grounding arrangement consisting of a horizontal electrode (galvanized steel strip with a cross-section 4 x 30 mm), depth of 0.5 meter, and 8 vertical electrodes (steel copper-clad pins with a diameter of 14 mm), 3 m long;
- interconnection of vertical and horizontal electrodes is carried out using clamp ZZ-005-064;
- current collector is interconnected with the output of the galvanized ground strip using control clamp GL-11562A;
- the design of the grounding arrangement corresponds to clause 1.7.55 of the EIC. Grounding arrangement of protective grounding and grounding for lightning discharges are common. Any grounding arrangement may be used as a protective grounding electrode.
The location of the elements of the lightning protection system and the grounding arrangement is shown in the drawing below. The depicted protection area corresponds to area B, constructed as per Appendix 3 of RD.
Boiler lightning protection zone (click to see in full scale)
Зона защиты Б РД 34.21.122-87 на отм. +11.230 - Protection zone B according to RD 34.21.122-87 at elev. +11.230
План кровли - Roof plan
Зона защиты Б РД 34.21.122-87 на отм. +12.000 - Protection zone B according to RD 34.21.122-87 at elev. +12.000
Условные обозначения - Legend
The activities are made in accordance with the EIC, Rev. 7, Chapter 1.7, SO and RD.
Table 1. List of required materials.
Do you have any questions about lightning protection for the cadet school or other facilities? Please contact the ZANDZ Technical Center!
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