Estimation of protection zone for lightning conductor

- A lightning conductor is a device, that is mounted on top of an elevated structure, such as a building or an construction with the aim to protect an object from direct thunderbolt.

- A lightning conductor (Fig.2.3) consists of the following elements:

- lightning rod (receiver) serves to provoke and receive lightning discharge and displays in the area of possible contact with the channel lightning;

- block of lightning rod;

- wire or electric conductor, that serves to direct electric charge from the lightning rod to the grounding device. They can be natural (such as reinforcement of concrete building structures of protection object) or artificial (different types of electric conductors);

- grounding device is a conductor or several interconnected conductors having electric contact with the ground such as the metal plate immersed in the ground.

Fig.2.3. Basic elements of lightning conductor

Rod lightning conductor is the most widely used as the simplest, cheapest and more reliable. Rope lightning conductor is less reliable compared to the rod and therefore they are used in the protection of objects of great length. In turn, reticulate lightning conductor is reliable in operation and widely used in the protection of buildings and structures of III Category. Spatial volume, in which building is protected from direct thunderbolt with definite degree of reliability, is called by protection zone of lightning conductor. Depending on the reliability degree the protection zones are divided in two types - A and B. Zone A has a reliability degree equal to 99.5% and higher, but zone B – equal to 95% and higher.

There are three types of lightning conductors - rod, rope and reticulate. A single rod lighting conductor is of height h<150 and has a protection zone, being a cone.

A protection zone of rod lightning conductor on ground level is determined by a circle with radius r₀ and at height h_x of protected object by circle with radius r_x. The height of the lightning conductor (cone) is h₀, Fig.2.4.

Fig. 2.4. Protection zone of the single rod lighting conductor: 1-at the ground level; 2-at the height (h_x) of the protected construction

The dimensions of protection zone of the single rod lightning conductor are determined by the following formulas:

For zone A:

1. Height and radius (at the ground level) of the protection zone:

(2.16)

where: h is the height of the single rod lightning conductor, m.

2. Radius of the protection zone at height object (h_x):

(2.17)

where: h _x is the height of protected object, m

For zone B:

1. Height and radius (at the ground level) of the protection zone:

(2.18)

2. Height of a single rod lightning conductor:

(2.19)

where: h_x is the height of protected object, m; r_x is the radius of object r_x,m.

The dimensions of protection zone B of the double rod lightning conductor (Fig.2.5) are determined by the following formulas:

For zone B:

1. Height and radius (at the ground level) of the protection zone:

(2.20)

2. Height of the double rod lightning conductor:

(2.21)

where: h_c is the internal height of protection zone, m; L is the distance between rods, m.

Fig. 2.5. Protection zone of the double rod lighting conductor: 1-at the ground level; 2-at the height (h_x) of the protected construction

The dimensions of protection zone of a cable lighting conductor (Fig.2.6) are determined by the following formulas:

For zone A:

Height and radius (at the ground level) of the protection zone:

(2.22)

Radii of the protection zone at object height (h_x):

(2.23)

For zone B:

Height and radius (at the ground level) of the protection zone:

(2.24)

Height of a cable lighting conductor:

(2.25)

where h_x is the height of protected object, m; r_x is the radius of the object, m.

Fig.2.6. Protection zone of a cable lighting conductor: 1 - at the ground level; 2 - at the height (h_x) of the protected object (a is the distance between abutments)

Example: D etermine the basic parameters of protection zone B of a single /double rod and cable lighting conductors to protect residential building from direct thunderbolt (input data for variant № 1).

A single rod lighting conductor:

1. The height of a single rod (h) lighting conductor is determined by the formula (2.19), m:

.

2. The height (h₀) and radius (r₀) of the protection zone B are calculated by the formulas (2.18), m:

, .

A double rod lighting conductor:

3. The height of the double rod lighting conductor (2.19), m:

.

4. The height (h₀) and radius (r₀) of the protection zone B are calculated by the formula (2.20), m:

, .

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