The ZANDZ Technical Center has received a request to calculate the lightning protection system for the electrical signal tower. Let us further consider a solution proposed by our specialists.
Facility: electrical signal tower (EST);
Dimensions: 38 m x 23 m x 11.68 m;
Soil resistivity: 100 Ohm*m.
calculate the lightning protection system;
calculate the grounding device.
Lightning protection and grounding of the building are made in accordance with:
PROTECTIONS OF BUILDINGS, STRUCTURES AND INDUSTRIAL COMMUNICATIONS", hereinafter referred to as SO;
RD 34.21.122 87 "INSTRUCTIONS FOR MOUNTING LIGHTING PROTECTION OF BUILDINGS AND STRUCTURES", hereinafter to as RD.
The facility is classified as "conventional" from the viewpoint of SO and as Category III of the lightning protection according to RD.
A set of measures to provide the necessary requirements to the lightning protection system and to the grounding arrangement for the EST includes the following solutions:
1. The facility lightning protection is made using lightning arresters on 2 m concrete foundations (GL-21131). Connection to current collectors is performed using holders included in the lightning arrester set.
2. A steel copper-plated wire d8 mm (GL-11149) is used as a lightning arrester.
3. Current collectors are installed using clamp GL-11711 on the roof and GL-11703A on vertical surfaces. The clamp installation spacing 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 must be connected to the current collector using clamps GL-11545A. Stairs, railings, are attached using the terminal-clamp GL-11514N.
6. 3 m copper-plated steel electrodes in the locations of the current collector downdrops are used as vertical grounding electrodes.
7. The copper-plated steel strip with a cross-section 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.
8. According to the EIC, 7th rev., item 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 usually should be common.
9. If there are reinforced concrete structures, they should be connected to current collectors/grounding arrangement.
10. Connection to the grounding arrangement is made with clamps ZZ-005-064.
Calculation results carried out using software developed by the G.M. Krzhizhanovsky Energy Institute, JSC ENIN, OJSC:
The occurrence of lightning strokes into the ground is 4 strokes/sq. km per year
The total number of strikes into the system is 0.043 (once every 23 years).
Total number of blowouts is 0.0031 (once per 323 years).
System reliability is 0.929;
The probability of breakout into all facilities of the system is 0.071.
Ground terminal resistance calculation:
Vertical electrode resistance:
Ом - Ohm
where ρeq is equivalent soil resistivity, 100 Ohm·m;
L vertical electrode length, 3 m;
d is diameter of the vertical electrode, 0.014 m;
T deepening - is the distance from the ground surface to the ground electrode, 2 m;
Ом - Ohm
where t is electrode top depth, 0.5 m.
Horizontal electrode resistance:
Ом - Ohm
where ρ is soil resistivity, 100 Ohm·m;
b is horizontal electrode width, 0.03 m;
h is horizontal electrode depth, 0.5 m;
Lгор is horizontal electrode length, 45 m.
Electrical impedance of the grounding arrangement:
Ом - Ohm
where n is a number of sets, vertical grounding arrangements - 3 pcs, horizontal grounding arrangement - 1 pc;
Kutil is utilization rate, 0.81.
The rated resistance of the grounding arrangement is 3,86 Ohms.
Условные обозначения - Legend
Молниеприемник на бетонном основании высотой 2 м - 2 m lightning arrester on a concrete foundation
Проволока стальная омедненная диаметром 8 мм - Steel copper-plated wire diam. 8 mm
Полоса стальная омедненная сечением 30х4 мм - Steel copper-plated bar 30 x 4 mm
Зажим для подключения проводника - Clamp for connecting wire
Опуск токоотвода - Current collector downdrop
Вертикальный заземлитель длиной 3 м - 3 m vertical grounding device
Figure 1. Equipment layout.
The list of necessary materials is given in Table 1.
Table 1. List of needed materials.
|№||Part number||Name||Quantity, pcs.||Unit weight, kg||Note|
|1.||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)||9|
|2.||GL-11149-50||GALMAR Copper-plated wire (D 8 mm / S 50 mm²; 50-meter coil)||4||0,41||Weight per 1 m|
|3.||GL-11545A||GALMAR Main conductor rain water gutter terminal (painted galvanized steel)||10||0,112|
|4.||GL-11514N||GALMAR Ring clamp on rainwater pipe for current collector (tinned copper)||10||0,076|
|5.||GL-11551A||GALMAR Conductor connection clamp (painted zinc-plated steel)||40||0,07|
|6.||GL-11711||GALMAR Flat roof terminal for the main conductor cable (D8 mm; plastic, concrete)||200||1,20|
|7.||GL-11703A||GALMAR Current collector facade clamp providing 15 mm elevation of the collector over the clamp (painted zinc-plated steel)||40||0,02||..|
|8.||GL-11075-10||GALMAR Copper-clad strip (30x4 mm/S 120 mm²; 10-meter strip bundle)||1||0,98||Weight per 1 m|
|9.||GL-11075-50||GALMAR Copper-plated strip (30 * 4 mm / S 120 mm²; 50-meter strip bundle)||1||0,98||Weight per 1 m|
|10.||ZZ-001-065||ZANDZ Copper-plated threaded grounding rod (D14; 1.5 m)||6||2,00|
|11.||ZZ-002-061||ZANDZ Threaded coupling||4||0,08|
|13.||ZZ-004-060||ZANDZ Guide head for jackhammer attachment||2||0,09|
|14.||ZZ-005-064||ZANDZ Conductor connection terminal (up to 40 mm)||8||0,312|
|15.||ZZ-006-000||ZANDZ Conductive grease||1||0,10|
|16.||ZZ-007-030||ZANDZ Waterproofing tape||6||0,40|
|17.||ZZ-008-000||ZANDZ Attachment to the hammer (SDS max)||1||0,50|
Do you have any questions regarding lightning protection and grounding for the EST? Please contact the ZANDZ Technical Center.