Lightning Protection and Grounding for a Lightning Arrester and Grounding Electrodes Warehouse

As it is known, grounding and lightning protection should be provided for all newly built facilities. In our example calculation, we will learn how to protect the lightning arrester and grounding electrode warehouse.

Initial data:

• Facility: Lightning arrester and grounding electrode warehouse;
• Dimensions: 84 m x 30 m x 9 m;
• Soil resistivity: 100 Ohm*m.

Task:
To calculate the lightning protection and grounding electrode system.

Solution:

The activities have been performed according to:

1. EIC Rev. 7 (hereinafter referred to as the EIC);
2. SO 153-34.21.122-2003 Instructions for Mounting Lightning Protection for Buildings, Structures, and Industrial Utilities (hereinafter referred to as SO);
3. 3. RD 34.21.122-87 Instructions for Mounting Lightning Protection for Buildings and Structures (hereinafter referred to as RD).

According to the EIC Rev. 7, item 1.7.101. the resistance of the grounding arrangement should not be more than 4 Ohm in any season of the year.

A set of measures to meet the necessary requirements to the lightning protection and grounding electrode warehouse includes the following solutions:

1. The facility is classified as Category II of the lightning protection.

2. The facility lightning protection is made using 7 m lightning arresters (ZZ-201-007-3) attached by holder brackets (distance between the feet is 1 m).

3. Venting shafts are protected with metal caps attached to current collectors.

4. A copper-plated steel wire (copper coating thickness is at least 70 μm), d8 mm (GL-11149) is used as a current collector.

5. Installation of current collectors is performed using clamps GL-11747A on the roof and GL-11703A on ramparts and vertical surfaces. The clamp installation interval is 0.8 to 1.0 m.

6. The multipurpose GL 11551A clamp is used to connect the rolled products over the length and in assemblies.

7. All metal elements located on the roof should be connected to current collectors.

8. Copper-plated steel electrodes 3 m long in the locations of the current collector downdrops are used as vertical ground 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.

9. 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.

10. If there are concrete-steel constructions, they shall be connected to down conductors/grounding device.

11. Connection to the grounding device is carried out using ZZ-005-064 clamps.

The results of calculation of protection zones according to SO:

h = 12,5 m;

Cone height according to SO, Table 3.4:

h0 = 0,8h = 10 m;

Cone radius according to SO, Table 3.4:

r0 = 0,8r = 10 m;

For the protection zone with the required reliability, radius rx at the height of h0 = 9 m is defined as follows:

м - m

Distance between the lightning arresters (maximum):

L = 21 m;

Limit distance between lightning arresters according to SO, Table 3.6:

There is not sagging height.

Расчет сопротивления заземляющего устройства:

Ground terminal resistance calculation: 

Верт - Vert Экв - Eq Ом - Ohm

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;

Horizontal electrode resistance:

Гор - Hor

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, 255 m.

Electrical impedance of the grounding arrangement:

ЗУ - GA

where n – is number of vertical electrodes, 12 pcs; horizontal electrode 1 pc;
kutil – is a set utilization ratio, 0.63

estimated resistance of the grounding arrangement is 1,16 Ohm, which is less than the required value of 4 Ohm.

Условные обозначения Legend
- молниеприемник-мачта высотой 7 м - 7 m lightning arrester
- проволока стальная омедненная диаметром 8 мм - steel copper-plated wire diam. 8 mm
- полоса стальная омедненная сечением 30х4 мм - steel copper-plated strip with cross-section 30 x 4 mm
- универсальный зажим-соединитель для проволоки - multi-purpose connecting clamp for wire
- зажим для подключения проводника - clamp for connecting wire
- опуск токоотвода - downdrop
- вертикальный заземлитель длиной 3 м - 3 m vertical grounding electrode

Figure 1. Equipment layout.

The list of necessary equipment and materials is provided in Table 1.

Table 1. List of needed materials.

Dear colleagues! This facility does not require such a high category of the lightning protection and the resistance level of the grounding arrangement. According to the standards, Level II and grounding resistance not more than 10 Ohm are sufficient. But such a responsible warehouse maintenance :) is worth an increased attention of the design engineer! The cobbler's children should have shoes!

Please accept congratulations on April 1st!

Contact us to get free calculations for lightning protection and grounding for any facility? We are happy to help you!

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