The ZANDZ Technical Center has received a request to develop the solution for a silo-type grain depot with the capacity of 5,000 tons with unloading to a vehicle. The advantage of the silo storage scheme is not only the possibility for long-term grain storage without compromising its quality but also the possibility to perform intensive unloading of large volumes of grains to various types of vehicles. Such buildings are often located on an open terrain, being a facility of increased attention for lightnings since their height is significantly greater than that of nearby structures.
From the viewpoint of protection from lightnings, the protected building is a metal structure having a significant thickness and cross-section with the guaranteed electrical coupling along its length. This gives an opportunity to use them as natural lightning protection elements subject to meeting the requirements of SO 153-34.21.122-2003 and RD 34.21.122-87. A special customer's requirement is that the lightning protection grounding resistance should not exceed 4 Ohms since it will be used for the facility automation systems.
The protected facility is classified as conventional in terms of lightning protection according to SO 153-34.21.122-2003 and to Category 3, Protection Zone B, according to RD 34.21.122-87.
To arrange the zone for protection of direct lightning strikes, lightning rods (7 m high attached to the metal structure, considering 1.5 m for attachment) and metal structures of the sites according to RD 34.21.122-87 item 2.11 and SO 153-34.21.122-2003 item 22.214.171.124-126.96.36.199 are used. Protection zone for a repeated lightning arrester is defined as a protection zone of pairwise adjacent lightning arresters h ≤ 150 m according to Appendix 3 to RD 34.21.122-87. For calculations, lightning rods are considered as natural lightning arresters.
Fig. 1. RD 34.21.122-87. Appendix 3. Lightning arrester protection zones
Protection zone (in a 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
Metal structures are used as current collectors according to items 1.6 and 2.12 of RD 34.21.122-87 and item 188.8.131.52 of SO 153-34.21.122-2003.
A set of measures to ensure the requirements for the grounding arrangement is based on 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 m, and 11 vertical electrodes (galvanized steel pins with a diameter of 16 mm), 3 m long;
- horizontal electrodes are connected to vertical electrodes and metal structures using bolt connections;
- the design of the grounding arrangement corresponds to item 1.7.55 of the EIC. Grounding arrangements for protective grounding and grounding for lightning discharges are common.
The location of elements of the lightning protection system and the grounding arrangement is shown in the figure below. The indicated protection zone conforms to zone B according to RD 34.21.122-87.
Fig. 2. Layout of lightning protection and grounding system for grain storage
Fig. 3. Installation of a clamp on the metal structure
Зажим - Clamp
Полоса - Bar
М/к - Metal structure
4 отв. Ф 12 мм - 4 holes, diam. 12 mm
Fig. 4. Hole spacing for clamp installation
Ground arrangement resistance calculation:
Vertical grounding arrangement resistance:
Верт - Vert.
Экв. - Eqv.
where ρ is equivalent soil resistivity, 100 Ohm*m;
L is vertical electrode length, 3 m;
d is vertical electrode diameter, 0.014 m;
T is depth;
t - is distance from the ground surface to the grounding electrode, 0.5 m;
м - m
Horizontal electrode resistance:
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, 225 m.
Electrical impedance of the grounding arrangement:
ЗУ - GA
Исп. гр. - Util
where n is number of vertical electrodes, 1 pc; horizontal electrode 1 pc;
kutil is a set utilization ratio, 0.7;
The estimated resistance of the grounding arrangement is 1.17 Ohm, which is less than the required value of 4 Ohm.
Table 1. List of required materials.
|No.||Part number||Name||Quantity, pcs.|
|Lightning protection system:|
|1.||ZZ-201-007-3||ZANDZ Lightning rod mast, vertical, 7 m high, with a set of 2 wall fasteners (stainless steel)||3|
|2.||ZZ-005-064||ZANDZ Conductor connection clamp (up to 40 mm)||28|
|3.||ZZ-001-255||ZANDZ Threaded galvanized grounding rod (D16; 1.5 m; M16)||22|
|4.||ZZ-002-251||ZANDZ Threaded galvanized connection coupling (M16)||12|
|5.||ZZ-003-250||ZANDZ Termination for galvanized grounding rods (M16; galvanized steel)||11|
|6.||ZZ-004-250||ZANDZ Guide head for jackhammer attachment (M16; galvanized steel)||5|
|7.||ZZ-006-000||ZANDZ Conductive grease||2|
|8.||ZZ-007-030||ZANDZ Waterproofing tape||6|
|9.||ZZ-008-000||ZANDZ Attachment to the hammer (SDS max)||1|
|10.||ZZ-502-304-52||ZANDZ Steel galvanized bar (30 * 4 mm; 52 m bundle)||5|
Do you have any questions about the lightning protection of the measurements system of the oil quality and quantity indicators or other facilities? Please contact the ZANDZ Technical Center!