How to protect a grain warehouse against lightning?

June 2, 2017

When grain is stored in a warehouse, in summer, a danger of ignition of both grain dust and dried grain exists. Lightning may be a reason of fire. This can be avoided by installing properly selected lightning protection and grounding equipment as well as by using the structural elements of the building. We will learn next about how to protect the grain depot from lightning.

How to Protect Grain Depot from Lightning?

Task:

To calculate the lightning protection system for a grain depot located in a modular building with the facade and the roof made of metal shaped sheets 0.7 mm thick.

Solution:

Calculations of the lightning protection are made in conformity with the following documents:

"Electrical Installations Code" (hereinafter referred to as the EIC), 7th edition.
"Guidelines for Arrangement of Lightning Protection of Buildings, Structures, and Industrial Utilities" SO 153-34.21.122-2003 (further – SO).
 "Guidelines for Arrangement of Lightning Protection of Buildings and Structures" RD 34.21.122-87 (further – RD).

Protection of buildings against lightning strikes is provided by using lightning arresters. Lightning arrester is a device that is elevated over the protected facility through which the lightning current goes into the ground bypassing the protected facility. It consists of a lightning rod that directly accepts the discharge of a lightning , a current collector, and a grounding electrode.

Description of the lightning protection system

A set of arrangements ensuring compliance with the lightning protection requirements is based on the following solutions:

1. To protect the roof from burns, two 4 m lightning rods ZZ-201-004 are installed. It is considered that 0.7 m of the rod length is used for securing.
2. Natural metal structures of the building are used as current collectors: 0.7 mm metal shaped sheets and a metal frame between with a continuous electrical coupling shall be provided.

A set of measures to ensure the requirements for the grounding arrangement is based on the following solutions:

1. A horizontal circuit is laid around the building. The circuit is made of a corrosion-resistant copper-plated steel bar GL-11075 with cross-section 4 x 30 mm, depth 0.5 m, distance to the building wall at least 1 m.
2. Four 3 m vertical electrodes are installed.
3. Connection of horizontal electrodes with vertical electrodes and the metal frame of the building is performed using ZZ-005-064.

Figure 1. Layout of lightning protection and grounding arrangement. The indicated protection zone corresponds to zone B according to RD

Protection reliability calculation

For calculation, the following initial data were used:

The density of lighting discharges into the ground is 4 strikes/sq. km per year.

The results of calculation of the lightning protection performed using software developed by OJSC Krzhizhanovsky Energy Institute (OJSC ENIN) are provided in Table 1.

Table 1. Results of lightning protection calculations

№	Facility	Lightning rod height, m	Protection reliability	Number of strikes into the facility, year - 1	Number of blowouts into the facility, year - 1
				Period of strikes, year	Period of blowouts, year
1	Grain depot	4	0,913	0,018	0,0016
				once per 56 years	once per 625 years

Figure 2. Installation of clamp ZZ-005-064 to metal structures

Зажим - Clamp
Полоса - Bar

Figure 3. Marking holes for installation of clamp ZZ-005-064

4 отв. Диам. 12 мм - 4 holes, diam. 12 mm

Calculation of a grounding arrangement

According to the EIC, Item 1.7.103, total dissipation resistance of ground terminal (including natural) of all repeated groundings of the PEN wire of each high-voltage line in any season of the year should not exceed 10 Ohm, respectively, with linear voltages 380 V of a three-phase source or 220 V of a single-phase source.

100 Ohm∙m is taken as an estimate soil resistivity.

Results of the grounding calculations performed by using the software developed by OJSC Krzhizhanovskiy Energy Institute (OJSC ENIN):

The estimated resistance of the grounding arrangement is 2.59 Ohm, which is less than the required value of 10 Ohm.

Table 2. List of required materials for lightning protection and grounding

№	Fig.	Part number	Product	Quantity
Lightning protection system
1.		ZZ-201-004	ZANDZ Vertical lightning mast, 4 m (stainless steel)	2
2.		ZZ-203-001	ZANDZ Wall fastening for lightning rod (stainless steel)	2
3.		GL-20022	GALMAR Clamp to lighting rods for current correctors (stainless steel)	2
Grounding arrangement
4.		ZZ-005-064	ZANDZ Зажим для подключения проводника (до 40 мм)	10
5.		GL-11075-50	ZANDZ Conductor connection clamp (up to 40 mm)	1
6.		GL-11075-20	GALMAR Copper-plated strip (30 * 4 mm / S 120 mm²; 50-meter strip bundle)	2
7.		ZZ-001-065	GALMAR Copper-plated bar (30 * 4 mm / S 120 mm²; bundle 20 meters)	8
8.		ZZ-002-061	ZANDZ Copper-plated threaded grounding rod (D14; 1.5 m)	5
9.		ZZ-003-061	ZANDZ Takeoff Tip	4
10.		ZZ-004-060	ZANDZ Guide head for jackhammer attachment	2
11.		ZZ-006-000	ZANDZ Conductive grease	1
12.		ZZ-007-030	ZANDZ Waterproofing tape	2
13.		ZZ-008-000	ZANDZ Attachment to the jackhammer (SDS max)	1
14.		ZZ-500-105	ZANDZ Grounding conductor (5 m; S25; single-wire; with a tip for bolt D8)	1

The listed equipment provides reliable protection from lightnings which has been proved by the calculations made in the software.

Do you have any questions about lightning protection and grounding of the grain depot?
Please, contact the ZANDZ Technical Center!

See also: