RU2382464C1 - Lightning protection device - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention is related to devices for protection of various purpose objects against direct thunderbolts. Device comprises lightning rod and earth lead. Lightning rod comprises metal mast and rod lightning collector. Besides metal mast is arranged in the form of conic structure with section radius that reduces from its base to top. Metal mast is installed inside shielding made of thin metal conductor set arranged with equal pitch. Radius of circumference, along which conductors are arranged, grows from shielding base to its top. Upper ends of conductors are fixed in upper part of metal mast by means of flanged joint. Flanged joint is installed inside mountaneous electrostatic crane. Rod lightning collector is rigidly fixed in the centre of metal mast, and metal mast is rigidly fixed on foundation. Lower part of metal mast is installed in reservoir with water. Earth lead is arranged in the form of multibeam structure communicated with water reservoir and made of pipes with drain holes, which make it possible to arrange sprinkling watering of soil.

EFFECT: elimination of sparking in area of combustible and explosive gaseous exhausts with simultaneous reduction of wind loads at structure.

6 cl, 3 dwg

Description

The invention relates to devices for protection against direct lightning strikes of objects for various purposes.

A device for lightning protection, including a rod lightning rod, is a traditional means of protecting ground objects from direct lightning strikes, known from the middle of the 18th century thanks to the work of Franklin. According to modern concepts, the action of a lightning rod is based on the fact that, rising above the protected object, it provides local amplification of the electric field of the atmosphere at its peak, which creates favorable conditions for the development of an ionized channel from it - the oncoming leader. Moving towards the lightning channel, he intercepts it, ensuring the defeat of the lightning rod, and not the protected object.

In recent decades, they have been trying to increase the effectiveness of protection against direct lightning strikes by creating devices that include so-called active lightning rods (see, for example, RU 2090968 C1, 09.20.1997, RU 2277444 C2, 06/10/2006, RU 2101819 C1, 01/10/1998, US 4016462 A, 04/05/1977, KR 100433011 B, 05/14/2004, etc.). They are based on various effects on the electric field or the state of the air at the top of the rod, which would facilitate earlier initiation of the oncoming leader.

Accepting lightning strikes, lightning rods of any type provide the discharge to the ground of a pulsed lightning current with an amplitude of tens to hundreds of kiloamperes. In this case, the potential of the lightning rod rises with respect to the zero potential of the remote “earth” due to the voltage drop on the grounding device of the lightning rod, as well as as a result of EMF magnetic induction. Its source is a magnetic field that rapidly grows at the front of a lightning current pulse, which propagates both along the lightning rod stand and through the lightning channel itself.

For a lightning current with a front duration of 10 μs and an amplitude of 100 kA (standardized by the normative document “Instructions for lightning protection of buildings, structures and industrial communications”, approved by order of the Ministry of Energy of Russia dated June 30, 2003, No. 280), the potential of a lightning rod with a typical grounding resistance of 10 Ohm is able to exceed 1000 kV. As a result of such a high voltage, an electric charge with a linear density of about 10 μC / m and higher is induced on the side surface of the lightning rod, which leads to a sharp increase in the radial component of the electric field. With practically used diameters of the lightning rod rack, the radial field exceeds the air ionization threshold, and thereby gives rise to short spark incomplete discharges. Due to the high temperature of the plasma in such channels, their contact with the zone of combustible gas emissions into the atmosphere causes a fire or explosion, similar to what happens, for example, when working with domestic gas electric lighters.

Current regulatory documents do not prevent the installation of lightning rods in areas of technological emissions of combustible and explosive gas mixtures. To exclude their ignition, it is necessary to reduce the field on the surface of the lightning rod below the ionization threshold of air. This can be done by increasing the radius of the rack, because in an extended structure, the field strength is inversely proportional to the radius of the conductor. In practice, we should talk about the radii of racks of tens of centimeters, which cannot be considered constructive due to unjustified metal costs and a sharp increase in wind loads, which are very significant at a lightning rod height of tens of meters. In addition, the radius of the rack due to the uneven distribution of the induced electric charge on it should increase from the base to the top, which contradicts the design of the rack for strength reasons.

The objective of the present invention is to provide a device for lightning protection, which eliminates the above structural contradictions, namely: to exclude sparking in the area of combustible and explosive gas emissions while reducing wind loads on the structure.

The problem is solved in that in a device for lightning protection, including a rod lightning conductor, consisting of a metal mast, a pin lightning rod, and an earthing switch, according to the invention, the metal mast is made in the form of a conical structure with a section radius decreasing from its base to the top, and the metal mast is placed inside the shielding, consisting of a set of thin metal conductors installed with equal pitch, while the radius of the circle along which the conductors are installed on melts from the base of the sheath to its apex, and the upper ends of the conductors are fixed in the upper part of the metal mast by means of a flange connection, while the flange connection itself is placed inside the toroidal electrostatic shield, and the rod lightning rod is rigidly fixed in the center of the metal mast, and the metal mast itself is rigidly fixed to the foundation, and its lower part is installed in a tank with water, and the ground electrode is made in the form of a multi-beam design, in communication with the tank with water and made from pipes with drainage holes that allow drip irrigation of the soil.

The problem is also solved by the fact that the height of the shielding is 80% of the total height of the lightning rod.

In addition, the shielding is attached to the metal mast of the lightning rod at a height of 2 m above ground level.

The problem is also solved by the fact that the radius of the flange connection is 0.2 m higher than the radius of the circle on which the conductors are placed.

In addition, the electrostatic screen is made with a radius of the cross section forming the torus of about 0.15 m

It is also important that the number of beams in the design of the ground electrode system is set taking into account the specific resistance of the soil and the maximum allowable lightning current to ensure a decrease in the field inside the protection zone below the ionization threshold of air.

The technical result of the claimed invention is the development of an intrinsically safe device for lightning protection, which can be placed in a space filled with explosive and fire hazardous gas emissions.

Figure 1 shows a General view of a rod lightning rod.

Figure 2 shows the design of the ground electrode.

Figure 3 shows the placement of containers for drip wetting of the soil.

The device for lightning protection consists of a metal mast 1, which is made in the form of a cone, a rod lightning rod 2 and an earthing switch 3. A shield sheath 4 consisting of a set of thin conductors 5 is rigidly attached to the metal mast. The upper ends of the conductors 5 are mounted on the metal mast 1 by means of a flange connection (not shown in Fig.), which is placed inside a toroidal electrostatic screen 6. The rod lightning rod 2 is rigidly fixed in the center of the metal mast 1.

The metal mast 1 is rigidly fixed to the foundation 7, and its lower part is installed in a tank with water 8, and the ground electrode 3 is made in the form of a multi-beam design, connected with a tank with water 8, and made of pipes 9 with drainage holes that allow for drip irrigation of soil .

The device operates as follows.

The number of conductors 5 and the radii of the circumference of the shielding sheath 4, along which they are located in the upper and lower parts of the mast 1, are chosen so that the electric field strength at any point in the structure in contact with hazardous gas emissions does not exceed the ionization threshold of air (E _ion = 3000δ kV / m, where δ is the relative density of air). The initial data for calculating the geometric parameters of the shielding are:

- the amplitude and time parameters of the allowable current pulse of lightning,

- the value of the impulse grounding resistance of the lightning rod,

- the geometric dimensions of the grounding buses and the plan for their placement in the ground,

- lightning rod height.

The calculation technique is based on the known principles of electrodynamics and should be performed using specialized software. For example, for a lightning rod 30 m high, computer calculations lead to the following functional dependences between the electric field on the external surface E, the potential on the grounding device U, the number of conductors N and the radius of the circle of the lightning rod support along which they are placed: if, for example, an allowable threshold of electric field strength at the place of installation of the lightning rod 2500 kV / m, and the potential on the ground electrode when the lightning current spreads rises to 2000 kV (E / U = 1.25), then, using conductors with a radius of 5 mm, you can limit yourself to instruction of 50 conductors, if you place them on a circle with a radius of 0.4-0.8 m. Under the same conditions, the number of conductors with a radius of 2.5 mm increases to about 100. Both versions lead to the fact that when placing conductors around a circle with a radius 0.6 m effective section of the shell, which determines the wind load, is reduced by more than 4 times compared with the solid structure.

The dimensions of the electrostatic screen 6 are selected so as to guarantee a decrease in the electric field to the threshold of ionization of the air at the attachment points of the conductors 5 forming the shielding 4.

To increase the efficiency of reducing the electric field on the side surface of the lightning rod, its grounding device 3 should provide the most uniform distribution of potential on the earth's surface within the widest possible radius. In the extreme situation, when the earth's surface is metallized within a circle with a radius of 2-3 heights, the electric charge and the electric field on the surface of the side lightning rod would completely cease to depend on the grounding resistance.

A good technical effect is obtained when using multi-beam grounding conductors 3 with transverse connections between beams 15-20 m long. Examples of grounding conductors of a similar design like “grounding web” are presented in FIG. 2. The earthing switch is an integral element of an intrinsically safe lightning conductor. The specific design of the ground electrode is selected depending on the specific resistance of the soil and the required ground resistance.

The beneficial effect of a multipath ground electrode system is manifested as follows.

When the lightning current spreads, the pipes 9 of the ground electrode 3 take the same potential as the base of the lightning rod. The proximity of the pipes to the surface of the earth determines a comparable potential on the surface above the pipes. The electric charge that occurs there creates a noticeable fraction of the potential on the side surface of the lightning rod, as a result of which the intrinsic charge of the conductors forming this surface decreases within a few tens of percent, limiting the increase in the radial component of the electric field strength there.

Seasonal variation of grounding resistance due to changes in soil moisture is known from operating experience. In dry summer periods due to dehydration, the grounding resistance of a lightning rod can increase dramatically, thereby increasing the risk of sparking in hazardous areas. For seasonal stabilization of grounding resistance in a lightning rod, a drip irrigation system is provided. To this end, all underground grounding pipes 9 are provided with drainage holes along the side surface. The metal mast of lightning rod 1 is placed with its base in a container of water 8. The signal for starting watering is supplied by a sensor (not shown in Fig.), Which constantly monitors the grounding resistance of the ground electrode. If the grounding resistance exceeds the maximum permissible value, the sensor issues a command that, after processing by the converter, controls an electrically operated hydraulic valve (not shown in Fig.), Which allows liquid from tank 8 to drip irrigation pipes 9. Watering time is limited by a command from the soil moisture sensor, which, after treatment with a converter, closes the hydraulic valve.

Thus, the implementation of the device for lightning protection with a side shielding conical shell, consisting of a set of thin conductors, makes it intrinsically safe, and its grounding device provides the most uniform distribution of potential on the earth's surface within the maximum radius, which allows you to place the proposed device for lightning protection in space filled with explosive and fire hazardous gas emissions.

Claims (6)

1. A device for lightning protection, including a rod lightning conductor, consisting of a metal mast and a rod lightning rod, and an earthing switch, characterized in that the metal mast is made in the form of a conical structure with a section radius decreasing from its base to the top, and the metal mast is placed inside the shielding consisting of a set of thin metal conductors installed with equal pitch, while the radius of the circle along which the conductors are installed increases from the base of the shell to the top, and the upper ends of the conductors are fixed in the upper part of the metal mast by means of a flange connection, while the flange connection itself is placed inside the toroidal electrostatic screen, and the rod lightning rod is rigidly fixed in the center of the metal mast, and the metal mast itself is rigidly fixed to the foundation, and its lower the part is installed in a tank with water, and the ground electrode is made in the form of a multi-beam design, in communication with the tank with water, and made of pipes with drainage holes, allowing to produce drip irrigation of the soil. 2. The device for lightning protection according to claim 1, characterized in that the height of the shielding is 80% of the total height of the lightning rod. 3. The device for lightning protection according to claim 1, characterized in that the shielding is attached to the metal mast of the lightning rod at a height of 2 m above ground level. 4. The device for lightning protection according to claim 1, characterized in that the radius of the flange connection is 0.2 m greater than the radius of the circle on which the conductors are placed. 5. The device for lightning protection according to claim 1, characterized in that the electrostatic screen is made with a cross-section radius of the generatrix of the torus of about 0.15 m 6. The device for lightning protection according to claim 1, characterized in that the number of rays in the design of the ground electrode is set taking into account the soil resistivity and the maximum allowable lightning current to ensure a decrease in the field inside the protection zone below the air ionization threshold.

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