What are the lightning protection devices? Brief introduction of lightning protection device
May 23, 2022
The whole set of lightning protection devices can be divided into lightning receptors, down conductors, lightning protection devices, grounding devices, and lightning protection devices are devices that prevent being struck by lightning through modern electrical and other technologies. The lightning protection device in the lightning protection device can be roughly divided into: power lightning protection device, power protection socket, antenna feeder protector, signal lightning protection device, etc.
Lightning rods, lightning wires, lightning nets and lightning strips are all lightning receptors. They all use their prominence above the protected object to lead the lightning to themselves, and then discharge the lightning current through the down-conductor and grounding device. the earth to protect the protected object from lightning strikes. The material used in the air-termination device should meet the requirements of mechanical strength and corrosion resistance, and should also have sufficient thermal stability to withstand the thermal damage of lightning current.
(1) Lightning rods are generally made of galvanized round steel or steel pipes with a diameter of about 20mm, a length of about 2500mm, and the ends are pointed. Lightning rods are mainly used to protect towering and isolated buildings or structures and their surrounding facilities, and are also commonly used to protect outdoor power transformation and distribution devices.
(2) The lightning protection net uses galvanized round steel or flat steel to set lightning protection lines along the eaves of the roof, and then uses the same steel pipe to make 6×6m or 6×10m or 10×10m squares. Lightning protection nets are mainly used for buildings with flat or sloping roofs and large roof areas.
(3) The lightning protection belt is set around the building with galvanized round steel or flat steel. The lightning protection belt is mainly used to protect the vertical sides of high-rise buildings from lightning strikes. It forms a complete lightning protection system together with the lightning rod or lightning protection net on the roof.
(4) The lightning protection line is generally erected with a plated cast steel strand with a cross-sectional area of not less than 35mm2 and the overhead line on the same pole and tower. The erection method and sag requirements are the same as those of the overhead line, and are connected to the grounding device at the middle parts of the head and tail. The lightning protection line is mainly used to protect the overhead line erected on the same pole and its surrounding facilities. See Table 8-1 for the minimum size of the air-termination device. When the air-termination device is installed above the chimney, due to the corrosive effect of the flue gas, the size should be appropriately increased.
Two: lightning protection device
The lightning arrester is connected in parallel to the protected equipment or facility. Normally, the device is insulated from the ground. When there is a lightning strike overvoltage, the device and the ground are turned from insulation to conduction, and the breakdown discharge will lead to the lightning current or overvoltage into the ground. play a protective role. After the overvoltage is terminated, the lightning arrester quickly returns to the blocked state and resumes normal operation. Lightning arresters are mainly used to protect electrical equipment and power lines, and are also used as safety measures to prevent high voltage from entering the room. The arresters have protective gaps, tubular arresters, valve arresters and zinc oxide arresters.
Low-voltage systems have power surge protectors and signal surge protectors, also called lightning arresters.
(1) Protective clearance
The protective gap is made by using the principle of high-voltage charged body breaking through the air gap. It has a simple structure, low price, and is easy to make, but its performance is poor. It is generally used on lines with low voltage and less important.
(2) Tubular arrester
Tubular arresters are mainly composed of porcelain sleeves, arc extinguishing tubes and internal and external gaps. They have complex structures and are often used in 10kV distribution lines as lightning protection for electrical equipment such as transformers, switches, capacitors, and cable heads.
(3) Valve type arrester
Valve-type arrester is the most commonly used arrester for high-voltage lines, high-voltage electrical appliances, and it is mainly composed of porcelain sleeves, spark gaps and nonlinear resistors. Lightning protection, suitable for AC and DC power grids, not limited by capacity, line length, short-circuit current, etc.
(4) Zinc oxide arrester
Zinc oxide arrester is a new type of arrester. It adopts polycrystalline semiconductor ceramic resistors sintered with non-linear high-quality zinc oxide and bismuth oxide metal oxides, which cancels the spark gap and improves the reliability of protection. It is characterized by no discharge delay, no power frequency freewheeling after atmospheric overvoltage, can withstand various lightning strikes, low residual voltage, large current capacity, long service life, long use for 0.25--550kV electrical systems and electrical equipment. Lightning protection and overvoltage protection are also suitable for overvoltage protection on the low voltage side.
(5) Surge protector
Surge protector, also known as lightning arrester, is an electronic device that provides safety protection for various electronic equipment, instrumentation, and communication lines. When a surge current or voltage is suddenly generated in an electrical circuit or communication line due to external interference, the surge protector can conduct and shun the current in a very short period of time, thereby avoiding damage to other equipment in the circuit by the surge.
Power surge protector, suitable for AC 50/60HZ, rated voltage 220V/380V power supply system, to protect indirect lightning and direct lightning effects or other transient overvoltage surges, suitable for family homes, the tertiary industry and Requirements for surge protection in the industrial sector.
The signal surge protector is suitable for lightning protection of various signal lines such as network RS485 RS232 RS422 audio broadcast lines and other signal lines.
Three: Lightning protection leads down the line
The down-conductor of the lightning protection device should meet the requirements of mechanical strength, corrosion resistance and thermal stability.
(1) The down conductor is generally made of round steel or flat steel, and its size and anti-corrosion requirements are the same as those of lightning protection net and lightning protection belt. Use steel strands as down conductors, and the cross-sectional area shall not be less than 25mm2. When using non-ferrous metal wires as down leads, copper wires with a cross-sectional area of not less than 16mm2 should be used.
(2) The down-conductor should be laid along the outer wall of the building, and should avoid bending and be grounded through the shortest way.
(3) When using multiple down-conductors, in order to facilitate the grounding resistance and check the connection of down-conductors and grounding wires, a disconnect card should be installed at a height of about 1.8m between each down-conductor and the ground.
(4) When multiple down conductors are used, the first and second types of lightning protection buildings shall have at least two down conductors, and the distance between them shall not be greater than 12m and 18m respectively; the perimeter of the third type of lightning protection buildings shall exceed When the height is 25m or more than 40m, there should also be two down conductors, and the distance between them should not be greater than 25m.
(5) In places susceptible to mechanical damage, a section of downconducting from 0.3m below the ground to 1.7m above the ground should be protected by bamboo pipes, angle steel or steel pipes. When angle steel or steel pipe is used for protection, it should be connected with down-conductor to reduce the reactance when passing lightning current.
(6) If the cross section of the down conductor is corroded by more than 30%, it should be replaced.
Four: lightning protection grounding device
The grounding device is an important part of the lightning protection device. The grounding device discharges the lightning current to the ground, limiting the voltage of the lightning protection device to the ground from being too high. In addition to the independent lightning rod, the lightning protection grounding device can be shared with other grounding devices on the premise that the grounding resistance meets the requirements.
(1) Lightning protection grounding device material. The material used for the lightning protection grounding device should be larger than that of the general grounding device. The lightning protection grounding device should be checked for thermal stability.
(2) Lightning protection grounding resistance generally refers to the impact grounding resistance, and the grounding resistance value depends on the type of lightning protection and the type of building. The impact grounding resistance of the independent lightning rod should generally not be greater than 10Ω; for less important third-class buildings, it can be relaxed to 30Ω. The power frequency grounding resistance of the lightning protection device should not be greater than 10Ω. The grounding resistance and impact grounding resistance of the lightning intrusion wave should not be greater than 5-30Ω, among which, the grounding resistance of the valve-type arrester should not be greater than 5-10Ω.
(3) Suppression of step voltage. In order to prevent the step voltage from hurting people, the distance between the direct lightning protection grounding device and the entrances and exits of buildings and structures and pedestrian crossings should not be less than 3m. When less than 3m, one of the following measures should be taken:
①The horizontal grounding body is partially buried more than 1m deep;
②The horizontal grounding body is partially covered with insulation (for example, covered with an asphalt layer with a thickness of 50-8Ocm);
③ The asphalt pavement with a width exceeding the grounding body by 2m and a thickness of 50-8Ocm shall be laid;
④Buried hat brim type or other types of equalizing strips.