3. 1, external lightning protection system design-external lightning protection system, mainly considering lightning protection and grounding.
3. 1. 1, lightning receiver system:
Single-point protection generally adopts φ 10- 18 hot-dip galvanized round steel, or water pipes and professional lightning rods, and the height is calculated according to the "rolling ball method" specified in GB50057-90(2000 edition). In order to protect buildings, the conventional practice is to use φ 10- 12 hot-dip galvanized round steel and lay it around the parapet. If the area of the building is too large, it is necessary to arrange a shielding net on the floor to form a whole lightning protection system together with the lightning protection belt. Details of lightning protection zone are as follows:
Schematic diagram of lightning protection area layout
Schematic diagram of lightning protection belt installation
Description: All materials used are hot-dip galvanized round steel. The diameter is φ 8- 12. The total length of the support card is 2 1cm. As shown in the figure, bend a 5 cm long lap section with lightning protection belt as a welding fixture. Drill a hole with a depth of 6cm on the daughter's wall every 1 m, and the diameter is the same as that of the round steel. For repairs.
The above is the design of conventional lightning protection zone. If it is because of special needs, an independent lightning rod can be designed. The lightning rod also calculates the protection range of the lightning rod according to the "rolling ball method". The calculation formula of engineering experience can be roughly "triangle method"
That is, a building whose protection radius is equal to the height of lightning rod, that is, an equilateral triangle. As shown in the figure:
H: height of lightning rod; R: protection radius, h = R.
Two or three types of buildings, the protection radius is:
At this time, the proportional relationship between the protection radius and the height of the lightning rod is: r = h.
3. 1.2, grounding system design:
According to the requirements of GB50057-94, we can use hot-dip galvanized angle steel and hot-dip galvanized flat steel as materials to make grounding grid. The general requirements of grounding grid are that the building grounding is not more than 30 ohms, the power supply grounding is not more than 10 ohms, and the common weak current system grounding is not more than 4 ohms; If public grounding is adopted, it is required not to exceed 1 Ω. In the actual construction process, according to the specific situation, using different combinations and optimizing materials can achieve the purpose of optimizing design. The following is a design example of a traditional grounding grid:
Layout plan of common artificial grounding grid
General grounding grid construction details
Description:
The network consists of vertical grounding body (L45×45@2000 hot-dip galvanized angle steel), horizontal grounding body (40×4mm hot-dip galvanized flat steel) and grounding module (600*500*45mm). If the soil conditions are poor, such as soil resistivity greater than 300 Ω? M, long-acting drag reducer should be added.
The buried depth of grounding grid shall not be less than 0.5m, and the spacing between vertical grounding bodies is generally twice the depth of vertical grounding bodies. For artificial grounding network, the grounding terminal must be reserved as the system grounding point and test point.
Other grounding grid designs:
In special occasions, such as the building area is too small, or the soil environment is harsh, nonmetallic grounding modules or ion grounding rods can be used to solve the problem. There are no examples here.
3. 1.3, equipotential design:
The principle of equipotential is like two pools built at the same height and filled with water at the same height. Because they are connected by water pipes, there is no pressure difference between them, so there will be no water flow. For electric potential, similarly, when our devices and objects are connected by metal wires, the potential difference between them is zero, so there will be no current or discharge between them.
For external lightning protection, when the lightning protection connection and grounding have been processed, the equipotential treatment should be considered. Generally, it is metal water towers, water pipes, metal exposed objects, iron gates, iron window frames, etc. The roof shall be connected with 40*4mm hot-dip galvanized flat steel and connected with the down lead of lightning protection belt. All bare metal objects are at the same potential level, thus avoiding the current generated by uneven potential from harming people's safety and damaging equipment.
For the general computer room, equipotential connection is needed. Equipotential connection in computer room is generally realized by equalizing ring. That is, around the machine room, about 10cm from the ground, under the anti-static floor, a circle of copper tape (30*3mm) or hot-dip galvanized flat steel (40*4mm) is set around, and the column reinforcement of all buildings passing by is led out and welded on it; At the same time, metal objects such as equipment shell and metal window are all welded to the equalizing ring with wires, and then welded to the ground with flat steel or round steel through bus bars. As shown in the figure below:
3.2, internal lightning protection design
3.2. 1, lightning protection design of power supply system
Internal lightning protection can also be divided into two parts. One part is the power supply part. Because all equipment is inseparable from electricity, and the power supply circuit is the most harmful part of induced lightning as the main way to induce lightning and direct lightning. Therefore, it is very important to do a good job in lightning protection of power supply system.
1, according to the national standard GB50343-2004, three-level protection. The first stage adopts SPD which can prevent 10/350 waveform (that is, direct lightning waveform). In the second stage, SPD with 40KA flow capacity is used, and then the final power arrester is used at the equipment end to protect the equipment layer by layer to increase the safety factor of the equipment. The principle of three-level protection is as follows:
Through the above three levels of protection, the surge voltage caused by lightning strike is suppressed in a relatively safe range.
According to the latest Technical Specification for Lightning Protection of Building Electronic Information System (Table 4.3. 1 in GB50343), four-level protection should be considered for some equipment or important systems with high requirements or places with harsh environment, as shown in the following table:
Table 4.3. 1 lightning protection grade selection table for building electronic information system
Lightning protection grade electronic information system
Class A 1, large computing centers, large communication hubs, national financial centers, banks, airports, large ports, train hubs, etc.
2.A-level security system, such as the CCTV monitoring and alarm system of the National Cultural Relics Archives.
3, large electronic medical equipment, five-star hotel
Class b 1, medium-sized computing center, medium-sized communication hub, mobile communication base station, large stadium (gymnasium) monitoring system and securities center.
2. Bureau-level security systems, such as closed-circuit television monitoring and alarm systems for provincial cultural relics and archives.
3, radar station, microwave station, highway monitoring and charging system.
4. Medium-sized electronic medical equipment
5. Four-star hotel
Class C 1
2, large and medium-sized cable TV system.
3. Three-star and below hotels.
Class d general electronic information system equipment other than the above-mentioned classes A, B and C. ..
Combined with the actual situation, it is generally handled according to the ideas of low-voltage distribution room, building general distribution, floor distribution and front-end equipment.
According to the national regulations on low-voltage lightning protection, external metal lines must be buried more than 15 meters through metal pipe grooves before entering the building, and low-voltage lightning arresters should be installed at the incoming end of the building. It is necessary to install a general lightning arrester at the low voltage end of the incoming line of the power supply, so as to lead the lightning high voltage that may be introduced by the external line to the earth discharge, so as to ensure the safety of the connected equipment. Lightning overvoltage can be limited below 2000 volts by using lightning arrester. ..