The ZANDZ Technical Center has received a request to calculate the lightning protection system and grounding arrangement for a preschool education facility (PEF). Let's consider what solution was proposed by our specialists.
Initial data:
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1. Facility: a preschool education facility;
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2. Dimensions of the protected facility: 27 х 25 х 9; 12 m;
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3. Soil resistivity: 100 Ohm*m.
Task:
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To calculate the external lightning protection system.
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To calculate the grounding arrangement with the resistance not exceeding 10 Ohm (the EIC, item 1.7.103).
Solution:
The activities have been performed according to:
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SO 153-34.21.122-2003 Instructions for Mounting Lightning Protection for Buildings, Structures, and Industrial Utilities (hereinafter referred to as SO);
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RD 34.21.122-87 Instructions for Mounting Lightning Protection for Buildings and Structures (hereinafter referred to as RD).
The facility is classified as conventional according to SO and to Category 3 according to RD. The required system reliability should be at least 0.9..
A set of measures to meet the necessary requirements to the lightning protection system and grounding arrangement for the PEF includes the following solutions:
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The facility lightning protection is made using lightning arresters on 2 m concrete foundations (GL-21131).
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A copper-plated steel wire (copper coating thickness of at least 70 μm), d8 mm (GL 11149), is used as a current collector.
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Current collectors are installed using clamp ZZ-202-015 on the roof and GL-11703A on vertical surfaces. The clamp installation step is 0.8 to 1.0 m.
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The multipurpose GL 11551A clamp is used to connect the rolled products over the length and in assemblies.
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All metal elements located on the roof should be connected to current collectors.
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Copper-plated steel electrodes 3 m long in the locations of the current collector downdrops are used as vertical ground electrodes.
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The copper-plated steel bar with a cross-section of 30 x 4 mm, combining all vertical electrodes, is used as a horizontal grounding electrode. The distance to the facility foundation is at least 1 m. Strip deepening is 0.5 to 0.7 m.
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According to EIC-7 issue, par.1.7.55, Grounding devices for protective grounding of electrical installations for buildings and structures and the 2nd and 3rd categories lightning protection of these buildings and structures, as a rule, shall be common.
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If there are concrete-steel constructions, they shall be connected to down conductors/grounding device.
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Connection to the grounding device is carried out using ZZ-005-064 clamps.
Results of the calculations performed by using the software developed by OAO Krzhizhanovsky Energy Institute (OAO ENIN):
Density of lightning discharge into the ground is 4 strikes/square km/year;
The total number of strikes into the system is 0.041 (once every 24 years).
The total number of breakouts into the system is 0.0013 (once every 769 years).
The system's reliability is 0.967;
The probability of breakout into all facilities of the system is 0.033.
Ground terminal resistance calculation:
Vertical electrode resistance:
Верт - Vert
Экв - Eq
Ом - Ohm
where ρρeq is equivalent soil resistivity, 100 Ohm·m;м
L is vertical electrode length, 3 m;
d is vertical electrode diameter, 0.014 m;
T – depth; is the distance from the ground surface to the ground electrode;
where t is electrode top depth, 0.5 m.
Horizontal electrode resistance:
Гор - Hor
Ом - Ohm
where ρ is soil resistivity, 100 Ohm·m;
b is horizontal electrode width, 0.03 m;
h is horizontal electrode depth, 0.7 m;
Lhor is horizontal electrode length, 25 m.
Electrical impedance of the grounding arrangement:
ЗУ - GA
Ом - Ohm
where n is the number of kits, 3 pcs;
Kutil is utilization rate, 0.81.
Estimated resistance of a protective grounding arrangement is 5,35 Ohm, which conforms to the requirements of the EIC, Rev. 7, item 1.7.103 and RD, item 2.26.
The layout of the equipment is shown in Figure 1.
- Молниеприемник-мачта высотой 2 м - 2 m lightning rod
- Проволока омедненная стальная диаметром 8 мм - Steel copper-plated wire D 8 mm
- Полоса омедненная стальная сечением 30х4 мм - Steel copper-plated bar 30 x 4 mm
- Электрод D = 14 мм, L = 3 м - Electrode D = 14 mm, L = 3 m
Figure 1. Equipment layout.
The list of equipment and necessary materials is provided in Table 1.
Table 1. List of needed materials.
Do you have any questions regarding lightning protection and grounding for a preschool education facility? Please contact the ZANDZ Technical Center!
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