Task:
Object: shopping center (SC).
It is necessary to make lightning protection system. The right axis of the building is made of glass. All metal elements protruding over the roof of the building must be connected to down conductors.
Soil: clay loam.
Soil resisitivity: 100 Ohm*mPreferable grounding variant: artificial grounding device with the resistance nor mote than 10 Ohm.
Solution:
The calculations were performed in accordance with the EIC 7th ed., IS 153-34.21.122-2003 "Instructions for lightning protection of buildings, structures, and industrial communications" (hereinafter IS) and AD 34.21.122-87 "Instruction for lightning protection of buildings and structures" (hereinafter AD).
Shopping centers refer to ordinary constructions in terms of lightning protection in accordance with the IS and to category 3 according to the AD. The required reliability of lightning protection system - 0.9.
According to EIC-7, p. 1.7.103. The total speading resistance of the ground electrodes (including natural) of all repeated groundings of the PEN conductor of each overhead line at any time of the year should not exceed 10 ohms at line voltage of 380 V of the three-phase power supply or 220 V of a single-phase power source.
Lightning protectio is implemented in the form of the rod system - five air terminals masts 6 meters high, and organization of lightning protection mesh on the glass part of the building roof. The size of the cell of the lightning protection mesh is not more than 10x10m. Type of mesh - copper-bonded steel with the diameter of 8 mm, thickness of the coating 70 micron (GL-11149).
Fixation of mesh is carried out by means
The distance between the clamps - 0,8- 1,0 m. To connect the mesh over the length and in the mesh nodes, a universal clamp GL-11551A is used.
Air terminal masts are mounted on horizontal surfaces on three concrete bases (included into the kit).
Copper-bonded wire 8 mm in diameter is used as down conductors (GL-11149).
The distance between the mesh and the down conductors- not more than 25 m.
The grounding device is designed as a contour around the perimeter of the building. Horizontal conductor - copper-bonded steel tape 30x 4 mm (GL-11075). 8 copper bonded steel electrodes D=14 mm, L=3 m are used as vertical electrodes. Verical electrodes are installed in places of downdrop of down conductors. Distance from the building base not less than 1 m.
The results of the calculation performed by the software, developed by JSC "Energy Institute to the name of G. M. Krzizhanovsky" (JSC "ENIN"):
Taking the density of lightning strikes into the ground - 6.0 strikes / sq km per year;
the total number of breakthroughs (direct strikes into the objects bypassing lightning rods) - 0,016 (once in 58 years).
Protection reliability- 0,928.
Calculation of grounding device resistance:
Resistance of a vertical electrode:
where ρeq - equivalent soil resistivity, ohm · m; L - length of the vertical electrode, m; d - vertical electrode diameter, m; T- deepening - distance from the ground surface to the ground electrode, m;
Resistance of a horizontal electrode:
ρ - soil resistivity, Ohm* m; b - horizontal electrode tape width ,m; Lгор - horizontal electrode length, m.
where t - deepening of the electrode top, m
Impedance of the grounding device:
where n - number of kits; Kисп - utilization ratio;
The design resistance of the grounding device is 1.68 ohms, which is less than the permissible resistance of 10 ohms.
The list of required materials:
Appendix: the project is available in DWG and PDF formats
Files in the formats DWG and PDF are available for downloading only for authorized users.
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