3.1, external lightning protection system design - external lightning protection system, the main consideration of the two parts of the flash and grounding.
3.1.1, the flash system:
For single-point protection, generally Φ10-18 hot-dip galvanized round steel, or water pipe, professional lightning rod, set up in the protection of the point (surface) above the height of the calculation method, according to the GB50057-90 (2000 version) of the provisions of the "roller ball law "Calculation. For the protection of the building, the conventional method is to use Φ10-12 hot-dip galvanized round steel, laid along the daughter wall of a week. If the area of the building is too large, it is necessary to lay a lightning net on the floor, together with the lightning belt, to form an overall lightning system. Lightning belt samples are shown below:
Lightning belt layout schematic
Lightning belt installation schematic
Description: the use of materials, are hot-dip galvanized round steel. The diameter of Φ8-12 can be. The total length of the support card, 21cm, as shown in the figure, bending a 5cm long lap section, as a welded with the lightning belt. Drill a hole with a depth of 6cm every 1 meter on the daughter wall, the diameter of which is in line with the diameter of round steel. As fixed.
The above is a conventional lightning belt design. If because of special needs, you can design independent lightning rod. Lightning rod also according to the "ball method" to calculate the scope of protection of the needle. Engineering experience in calculating the formula, can be roughly "triangular method"
That is, a class of buildings, the radius of protection and lightning rod height is equal, that is, the shape of an equilateral triangle. As shown in the figure:
h: lightning rod height; R: protection radius, h = R
Two, three types of buildings, the protection radius is:
This time, the protection radius and the height of the lightning rod proportionality: 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 ground net. The general requirements of the ground network, building grounding is not greater than 30 ohms, power grounding shall not be greater than 10 ohms, ordinary weak power system grounding shall not be greater than 4 ohms; if the joint grounding method, it is required to be not greater than 1 ohms. In the actual construction process, depending on the specific circumstances, the use of non-useful combinations, optimize the material, you can achieve the purpose of optimizing the design. The following is an example of conventional ground network design:
Ordinary man site network layout plan
Ordinary ground network construction sample drawing
Description:
This network consists of vertical grounding body (L45×45@2000 hot-dip galvanized steel angle), horizontal grounding body (40×4mm hot-dip galvanized flat steel), grounding module (600*500*45mm) Composition, if the soil conditions are poor, such as soil resistivity is greater than 300Ω?m case, you should increase the long-lasting resistance reduction agent.
The burial depth of the ground network, shall not be less than 0.5m, the interval between the vertical grounding body, generally twice the depth of the vertical grounding body. Artificial ground network, be sure to reserve the end of the ground, as a system of grounding and testing points to use.
Other ground network design:
In special occasions, such as the construction area is too small, or the soil environment is poor, you can use non-metallic grounding module, or ion grounding rod, to solve the problem. This is not an example.
3.1.3, equipotential design:
The principle of equipotential, like two pools, construction at the same height, and equipped with the same height of water, since the water pipe connected up, because there is no pressure difference between them, and therefore will not appear the phenomenon of water flow. For potential, the same reason, when we equipment, between the objects, are connected with metal wires, the potential difference between them is zero, so there will be no electric current, or the phenomenon of mutual discharge.
For external lightning protection, flashover, grounding, etc. has been dealt with when we have to consider the treatment of equipotential. General roof of the metal water tower, water pipes, metal exposed objects, iron doors, iron window frames, etc., are required to use 40 * 4mm hot dip galvanized flat steel for connection, and received lightning belt lead line. So that all the exposed metal objects are at the same potential level, thus avoiding the potential for uneven, and produce the current, resulting in safety hazards to people and damage to equipment.
For general equipment room, are required to carry out equipotential connection. The equipotential connection of the equipment room, generally through the equalization of pressure ring to achieve. Is along the computer room around, from the ground above about 10cm, and is located under the anti-static floor position, the ring set a circle of copper tape (30 * 3mm), or hot-dip galvanized flat steel (40 * 4mm), and will be over the place of all the building's columns of reinforcing bars, lead to weld to the top; at the same time, including equipment shells, metal windows, and other metal objects, all welded with wires to the top of the equalizing ring, and then At the same time, including the equipment shell, metal windows, other metal objects, all with wires welded to the equalizing ring, and then through a sink, with flat steel or round steel welded to the ground. As shown in the figure below:
3.2, internal lightning protection design
3.2.1, power system lightning protection design
Internal lightning protection, can also be divided into two major parts. One part is the power supply part. Because all the equipment, are inseparable from the electricity, and the power line as the main induction of lightning and direct lightning path, so it is also the induction of lightning inside, the most harmful part. So do a good job in the power system lightning protection, it seems to be important.
1, according to the national standard GB50343-2004, three-level protection. The first level of protection against 10/350 waveform (i.e., direct lightning waveform) SPD. 40KA current capacity of the second level of SPD, and then at the equipment end, the use of the last level of power supply lightning protection, so that layer by layer protection, increase the safety factor of the equipment. The principle of the three-level protection is as follows:
Through the above three levels of protection, the surge voltage generated by the lightning strike, suppressed in a relatively safe range.
According to the latest "building electronic information systems lightning technical specifications" that is, GB50343 requirements of Table 4.3.1 requirements, some of the higher requirements of the equipment or important systems, or located in the environment is more severe place of electricity, should be considered for the fourth level of protection, as follows:
Table 4.3.1 building electronic information systems lightning protection level
Lightning protection level electronic information systems
A level 1, large computing centers, large communications hubs, national financial centers, banks, airports, large ports, train hubs, etc..
2, Class A security systems, such as national cultural relics, archives of closed-circuit television monitoring and alarm systems.
3, large-scale electronic medical equipment, five-star hotels
B level 1, medium-sized computing centers, medium-sized communication hubs, mobile communication base stations, large sports stadiums (stadiums) monitoring system, securities center.
2, bureau-level security systems, such as provincial cultural relics, archives, closed-circuit television monitoring and alarm system.
3, radar stations, microwave stations, highway monitoring and toll systems.
4, medium-sized electronic medical equipment
5, four-star hotels
C Level 1, small communication hubs, telecommunications bureaus
2, large and medium-sized cable television systems.
3, three-star hotels and below.
Level D In addition to the above A, B, C, the general purpose of the electronic information system equipment.
In conjunction with the actual combination, we generally follow such an idea according to the low-voltage distribution room, the building's general distribution, the floor distribution, equipment front-end such an idea to deal with.
According to the relevant provisions of the national low-voltage lightning protection, external metal lines into the building must be buried in the ground before wearing a metal pipe groove more than 15 meters into the building, and to add the building line into the end of the installation of low-voltage lightning protector. It must be done at the entry end of the power supply to install the low-voltage end of the total power supply lightning protector, the external lines may be introduced by the high voltage of lightning strikes to the earth discharge to ensure the safety of the equipment connected to the use of the lightning protector can be limited to the lightning over-voltage to 2000V or less.