Design of lightning protection for a stadium

Task

Facility: stadium of 67 x 44 m with the tribune of 35 x 7 x 7 m (L x W x H) 4 light towers with projectors are present (ZANDZ Vertical lightning rod 18 m, galvanized steel; with embedded fittings for placing under the foundation) along the stadium perimeter.

The specific soil resistivity: 100 Ohm·m.

The calculations and the design of the lightning protection system and grounding device with the resistance of 10 Ohms are required.

Solution

According to calculations and paragraph 2.26 of RD34.21.122-87, the grounding device for each light tower is made of 3 vertical electrodes (copper-bonded threaded rods D14, 1.5 m ZZ-001-065, 2 pieces per 1 electrode) and copper-bonded tape 30 x 4 GL-11075 connected with a clamp for connecting ZZ-005-064 conductor (see the full specification and links to the description of the equipment below).

Carry out waterproofing for bolt connections and allow for inspecting connections at any time.

Connect the grounding device to the metal base of the tower by welding.

The grounding device is laid at the depth of 0.5 m from the ground surface and at the distance of 1 m from the light tower. The lightning rod is provided for by the tower design.
According to paragraph 3.2.2.5 of IS 153-34.21.122-2003, the own structure of the tower (ZANDZ Vertical lightning rod 18 m; galvanized steel; with the embedded fittings for placing under the foundation) is used as a current collector. Electrical continuity between different parts is provided for a long term.

The grounding device is arranged at the nearest territory outside the protection zone of the underground communications. Its precise location is determined during construction.
For arrangement of the external grounding device, see drawings of this design.

Carry out installation of lightning protection and grounding according to EIC, ed. 7, RD 34.21.122-87 "Instructions for Lightning Protection of Buildings and Structures" and IS 153-34.21.122-2003 "Instructions for Lightning Protection of Buildings, Structures, and Industrial Communications".

The resistance calculation for the grounding device

Vertical electrode resistance:

Vertical electrode resistance

where ρ_экв is the equivalent specific soil resistivity, Ohm·m;

L is the vertical electrode length, m;

d is the vertical electrode diameter, m;

T is the depth, the distance from the ground surface to the ground electrode, m.

Horizontal electrode resistance:

Horizontal electrode resistance

where ρ is the specific soil resistivity, Ohm·m;

b is the horizontal electrode band width, m;

h is the horizontal grid depth, m;

Lг_ор is the horizontal electrode length, m.

formula-1

where t is the depth of the electrode top, m.

Impedance of the grounding device:

Impedance of the grounding device

where n is the number of kits;

k_исп is the utilization ratio.

formula-2

formula-3

formula-4

The design resistance of the grounding device is 8.84 Ohms, which is less than the permissible resistance of 10 Ohms.

According to RD34.21.122-87, this facility requires lightning protection of category III with the protection zone of type B.

The facility protection from the direct lightning strikes is performed using ZANDZ Vertical lightning rods 18 m of light towers with the following dimensions:

h_o = 0.92 * h = 0.92*18 = 16.56 m is the height of the protection zone cone,

where h = 18 m is the lightning rod height.

r_o = 1.5 * h = 1.5*18 = 27 m is the radius of the cone at the ground level;

h_c = h_o-0.14*(L-h) = 16.56-0.14*(67-18) = 9.7 m is the cone height in the centre of the double lightning rod;

where L = 67 m is the distance between the lightning rods.

r_cx = r_o*(h_c-h_x)/h_c = 27*(9.7-6) /9.7 = 10.3 m is the width of the horizontal section in the centre of the double lightning rod;

r_x = 1.5*(h-h_x/0.92) = 1.5*(18-6/0.92) = 17.22 m is the height of the cone at the level of the protected facility.

The list of required materials:

№	Fig.	Product item	Name	Quantity	Weight, unit, kg
1.		ZZ-001-065	ZANDZ Copper-bonded threaded grounding rod (D14; 1.5 m)	24	1,9
2.		ZZ-002-061	ZANDZ Threaded coupler	12	0,08
3.		GL-11703A	ZANDZ Starting tip	12	0,07
4.		ZZ-004-060	ZANDZ Driving head for jackhammer	5	0,09
5.		ZZ-005-064	ZANDZ Clamp for connecting conductor (up to 40 mm)	12	0,31
6.		ZZ-006-000	ZANDZ Conductive grease	4	0,19
7.		ZZ-007-030	ZANDZ Waterproof tape	12	0,442
8.		ZZ-008-000	ZANDZ Head for jackhammer (SDS max)	1	0,48
9.		GL-11402	GALMAR Inspection well	12	2,6
10.		GL-11075	GALMAR Copper-bonded tape 30 x 4 mm	48	0.98 (in meters)
11.		ZZ-201-018	ZANDZ Vertical lightning rod 18 m (galvanized steel; with embedded fittings for placing under the foundation)	4	-