Lightning protection of houses and outbuildings. Scheme, description

ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Lightning protection of houses and outbuildings. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Lightning protection

Lightning - this is an electrical discharge that occurs in the atmosphere between oppositely charged clouds, their parts, or between a cloud and the earth.

Most often, lightning strikes strike places that rise above the surrounding surface, the highest objects in the building array and pointed objects - towers, free-standing trees, chimneys, etc.

The probability of being struck by lightning is affected by the electrical conductivity of the layers of the earth closest to the surface, as well as the level of groundwater.

During a lightning discharge, an electric current of several thousand amperes flows through the struck object for hundreds of thousandths of a second, due to the discharge of atmospheric electricity. Mechanical, thermal and electromagnetic effects that accompany a lightning discharge can cause injury to people and animals, fire, destruction of buildings and the appearance of overvoltages in the wires, but lightning currents do not destroy metal conductors of a sufficiently large cross section. Under a sufficiently large cross section for steel, 30-50 mm can be taken, which corresponds to a wire with a diameter of 6-8 mm.

To protect buildings from lightning strikes, they construct lightning rods (Fig. 7), which are a lightning rod (a metal rod raised to an appropriate height), a current-removing descent and a ground electrode. The lightning rod takes the lightning strike and diverts the lightning current to the ground. The current-carrying descent from the lightning rod to the grounding conductor is laid as short as possible, avoiding bending the wire at an acute angle, otherwise a spark discharge may occur between closely spaced sections of the wire and, as a result, ignition.

Lightning protection of houses and outbuildings
Rice. 7. Lightning rod: 1 - lightning rod; 2 - down conductor; 3 - ground electrode; 4 - lightning rod from a pipe; 5 - welding; 6 - lightning rod; 7 - lightning rod from the corner; 8 - lightning rod made of wire with a cross section of 6-10 mm

The height of the lightning rod and the place of its installation are chosen so that it completely protects the building from a lightning strike. The effectiveness of a lightning rod is evaluated by its protective zone, the boundary of which is a conical surface with a tip at the top of the lightning rod and a base in the form of a circle with a radius one and a half times greater than the height. Everything inside the zone is sufficiently protected from direct lightning strikes.

Lightning rods protect buildings that rise above the rest of the buildings or trees by more than 25 m, and stand-alone buildings that are not part of the building array if they are far from the trees. Protection against direct lightning strikes is an integral part of the building design and is not related to its electrification. Build lightning protection in the process of construction.

In addition to lightning protection, you must also take care of surge protection.

The electromagnetic effects of a lightning discharge create increased potentials (overvoltages) in the wires adjacent to the overhead line. To prevent their penetration into the premises through the wires of the overhead line, the hooks on which the insulators are installed are grounded, and, if possible, valve arresters RVN-0,5 are mounted between the phase wire and the grounding outlet.

Grounding hooks does not provide complete protection against the introduction of dangerous potentials into buildings through the wires of overhead power lines, therefore, in rural areas during a thunderstorm, one should not approach the electrical wiring and wires of the radio broadcasting network at a distance of less than 0,3-0,5 m; touch devices connected to the electrical network; you should also not be closer than 3-5 m from the grounding descent.

Author: Bannikov E.A.

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