The ZANDZ Technical Center has received a request to calculate the lightning protection system for a cadet school. Extracts from BTI passport as well as description of the roof shape were provided as initial data.
- Facility: a cadet school.
- Extracts from BTI passport.
- Soil resistivity: 100 Ohm*m.
Task: To calculate the external lightning protection system and a grounding arrangement.
The activities have been performed according to:
- EIC, Rev. 7;
- SO 153-34.21.122-2003 Instructions for Mounting Lightning Protection for Buildings, Structures, and Industrial Utilities (hereinafter referred to as SO);
- RD 34.21.122-87 Instructions for Mounting Lightning Protection for Buildings and Structures (hereinafter referred to as RD).
The protected facility is classified as a conventional facility in terms of lightning protection according to SO and to Category 3 according to RD.
A set of arrangements to ensure compliance with the requirements of the lightning protection system for the cadet school is based on the following solutions:
- 1. The lightning protection of the facility is made using ridge lightning arresters (ZZ-201-002-16) attached using clamps ZZ-203-003 as well as using vertical elevations of current collectors by 1 m along the roof edges. 2 m lightning arresters on concrete foundations (GL-21131) are installed on flat roof sections.
2. A copper-plated steel wire (copper coating thickness of at least 70 μm), d8 mm (GL-11149) is used as a current collector.
3. Current collectors are installed using clamp GL-11747A on the roof and ZZ-202-015 on a flat roof, and GL-11703A on vertical surfaces. The clamp installation step is 0.8 to 1.0 m.
4. The multifunctional GL-11551A clamp is used to connect rolled products over the length and in assemblies.
5. All metal elements located on the roof should be connected to the current collectors.
6. 3 m copper-plated steel electrodes in the locations of current collector downdrops are used as vertical grounding electrodes. The copper-plated steel strip with a cross-section of 30 x 4 mm, combining all vertical electrodes, is used as a horizontal ground electrode. The distance to the facility foundation is at least 1 m. Strip deepening is 0.5 to 0.7 m.
7. According to the EIC, Rev. 7, item 1.7.55, Grounding devices for protective grounding of electrical installations for buildings and structures and Categories 2 and 3 and lightning protection of these buildings and structures usually shall be common.
8. If there are reinforced concrete structures, they should be connected to current collectors/to the grounding arrangement.
9. Connection to the grounding device is performed using ZZ-005-064 clamps.
Results of the calculations performed by using the software developed by OAO G.M. Krzhizhanovskiy Energy Institute (OAO ENIN):
The density of lighting discharge into the ground is 4 strikes/sq. km per year.
The total number of strikes into the system is 0.06 (once every 17 years).
The total amount of breakthroughs (the strikes directly into the facility bypassing lightning arresters) is 0.003 (once every 333 years).
System reliability is 0.95.
Ground terminal resistance calculation:
Vertical grounding arrangement resistance:
Верт - Vert
Экв - Eq
Ом - Ohm
where ρis equivalent soil resistivity, 100 Ohm·m;
L is vertical electrode length, 3 m;
d is vertical electrode diameter, 0.014 m;
T is deepening;
t is the distance from the ground surface to the grounding arrangement, 0.5 m;
м - 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 grounding depth, 0.7 m;
Lhor is horizontal electrode length, 513 m.
Electrical impedance of the grounding arrangement:
ЗУ - GA
where n is number of vertical grounding arrangements - 18 pcs; horizontal grounding arrangements - 1 pc;
kutil is utilization rate, 0.45;
Estimated resistance of the grounding arrangement is 0,92 Ohm.
Условные обозначения - Legend
Figure 1. Layout of grounding arrangement parts.
Table 1. List of needed materials.
|№||Part number||Name||Quantity, pcs.||Unit weight, kg||Note|
|1.||ZZ-201-002-16||ZANDZ Lightning arrester 2 meters high for installation in threaded holders (M16; stainless steel)||7||10|
|2.||ZZ-203-003||ZANDZ Ridge holder for a lightning arrester (thread M16; current collector connection d8-10mm; stainless steel)||7|
|3.||GL-21131||GALMAR Lightning arrester (2 meters; 1 m on a concrete foundation, zinc-plated steel; complete with the clamp for the stainless steel current collector)||14|
|4.||GL-11149-50||GALMAR Copper-plated wire (D 8 mm/S 50 mm²; 50-meter bundle)||19||0,41||Вес в метрах|
|5.||GL-11551A||GALMAR Conductor connection clamp (painted zinc-plated steel)||120||0,07|
|6.||GL-11747A||GALMAR Conductor roof clamp for the roof coated with metal shape / corrugated sheeting (painted galvanized steel)||540||0,05|
|7.||GL-11703A||GALMAR Current collector facade clamp providing 15 mm elevation of the collector over the clamp (painted zinc-plated steel)||190||0,02|
|8.||ZZ-202-015||ZANDZ Holder for a circular conductor on a flat roof (D 8 mm; plastic + concrete)||340||1,00|
|9.||GL-11075-50||GALMAR Copper-plated strip (30 * 4 mm / S 120 mm²; 50-meter strip bundle)||11||0,98||Вес в метрах|
|10.||GL-11075-20||GALMAR Copper-plated strip (30 * 4 mm/ S 120 mm²; 20-meter strip bundle)||1||0,98||Вес в метрах|
|11.||ZZ-001-065||ZANDZ Copper-plated threaded grounding rod (D14; 1,5 m)||36||2,00|
|12.||ZZ-002-061||ZANDZ Threaded coupling||19||0,08|
|14.||ZZ-004-060||ZANDZ Guide head for jackhammer attachment||8||0,09|
|15.||ZZ-005-064||ZANDZ Conductor connection terminal (up to 40 mm)||49||0,312|
|16.||ZZ-006-000||ZANDZ Conductive grease||2||0,10|
|17.||ZZ-007-030||ZANDZ Waterproofing tape||17||0,40|
|18.||ZZ-008-000||ZANDZ Attachment to the hammer (SDS max)||1||0,50|
Do you have any questions about lightning protection for the cadet school or other facilities? Please, contact the ZANDZ Technical Center!