According to the national standard "Lightning Protection Design Code for Buildings" GB50057-94 (2000 edition), the external lightning protection devices include flashover, lead wire and grounding device.
(1) flashover: according to the characteristics of the building and lightning protection level selection of the sky network, lightning belt or lightning rod. Outstanding metal objects outside the scope of protection, such as metal equipment, metal pipes, metal railings, billboards, aviation sign lights, etc., should be welded or stuck with the lightning protection system, constituting a unified conductive system. Metal decorations on the roof such as metal flag poles or meet the code requirements of the wall thickness of the metal roof, can be used as a flashover.
(2) lead: try to use the building of reinforced concrete columns within the diagonal reinforcement as a lead, the building of the fire ladder, steel columns and other metal components can also be used as a lead, but the lightning protection components should be connected to the electrical path.
(3) grounding device: the design of grounding device, when the foundation using silicate cement and the surrounding soil moisture content is not less than 4%, no waterproof layer on the surface of the foundation, you can use the foundation of the rebar as a grounding device (detailed instructions), if the foundation is plastic, rubber, linoleum and other waterproof materials wrapped or coated with asphalt waterproofing layer, shall not be utilized in the foundation of the rebar as a grounding device! At this time in the foundation groove around the laying of ring-type grounding device, and with the foundation of the rebar to make a reliable connection.
Two, internal lightning protection measures and lightning electromagnetic pulse
1 prevent side-strike lightning
If the protection range of the lightning rod according to the rolling ball method of calculation to determine the lightning rod may accept the space above the falling lightning, but the side of the incoming lightning can still hit in the lightning range of the curve of the curve in the space under the points, that is to say, in the lower part of the lightning rod within the space lightning rod protection rate is no longer 99%, but rather, in the lower part of the space, lightning rod protection rate is no longer 99%, but the lightning rod protection rate is no longer 99%. Protection rate is no longer 99%, but 50 ~ 80% or lower values, so we can not fully count on lightning rod, but also to prevent side-strike lightning. For example, if the building's lightning protection level is the second category, the 45 meters and above the outer wall of the railing, doors and windows and other larger metal objects should be connected to the lightning protection device.
2 equipotential connection
To do a good job of equipotential connection in the building, equipotential connection is aimed at reducing the need to protect against lightning in the space, a variety of metal parts and a variety of systems between the potential difference. Building lightning protection against direct lightning introduced a strong lightning current through the lead line into the ground, in the vicinity of the space to produce a strong electromagnetic field changes will be induced in the adjacent wires (including power lines and signal lines) on the lightning overvoltage, so the building lightning protection system is not only unable to protect the computer, but may be introduced into the lightning. Computer network systems and other equipment such as integrated circuit chips are very weak voltage resistance, usually below 100 volts, so it is necessary to establish an equipotential connection to reduce the potential difference, to ensure that computers, especially computer network systems, and other weak power system safety.
The main practice of equipotential:
① With connecting wires or over-voltage protector, will be in need of lightning protection in the space of lightning protection devices, electrical equipment, metal windows and doors, elevator rails, cable trays, all kinds of metal piping, and metal parts of the system of weak electricity (boxes, shells, racks), etc., welded or connected to each other to form a unified conductive system. Formation of the building's Faraday cage, thus avoiding the existence of potential difference between the grounding line to eliminate the generation of induced overvoltage.
② building structure of the whole building beams, slabs, columns, foundation of the rebar is part of the equipotential connection, should be welded or tied into a unified conductive system, to the integrated **** with grounding device.
③ from different directions and locations into the building lighting, power and weak power system of the pipeline, should be connected to the nearest building grounding connection plate or ring-type busbar (indoor can be used as a foundation ring beam or bearing beam, or another number of equipotential connections to do the busbar, outdoor for the perimeter of the ring-type grounding device).
3 weak equipment shielding
Shielding should be used as a weak system to reduce the interference of the necessary measures, shielding the main purpose is to prevent lightning electromagnetic pulse, in the electronic equipment and information equipment systems more buildings, should be based on the requirements of the lightning protection zoning and equipment, the building is made into a full shielding (external shielding), part of the shielding, partial shielding, or shielding of the equipment and piping, so that lightning strikes When the electromagnetic field layer by layer attenuation. The outside of the building (external walls) for full shielding to form a cage lightning protection is the most safe and reliable lightning protection design program. Therefore, the location of important microelectronic equipment such as weak room should be placed in the center of the building, deep or lower floors.
4 on the surge protector SPD
4.1 SPD in the power supply system in the installation location
(1) in the LPZOA zone and LPZOB zone and LPZl zone interface, in the line from the outdoor lead to the installation of the first level of SPD (generally for the voltage switching type SPD). Suggested installation location: at the main power inlet, such as the low voltage side of the transformer or inside the main distribution cabinet.
(2) When the voltage protection level of the SPD installed above plus the induced voltage of the leads at both ends of the protection of the equipment supplied by the subsequent switchboard, the second level of SPD should be installed in the level of the switchboard (generally voltage-limiting type), and its location is generally located in the LPZl zone and LPZ2 zone at the intersection of the interface. Suggested installation location: installed in the lower end of the distribution box with a large number of weak power, information system equipment or need to limit the transient overvoltage equipment, such as: floor distribution boxes, computer centers, telecommunication rooms, elevator control rooms, cable TV rooms, building automation rooms, security monitoring centers, fire control centers, industrial automation rooms, inverter equipment control rooms, hospital operating rooms, guardianship rooms, and electronic medical equipment equipped with the places of the distribution box. Inside the distribution box. In addition, all lead to the outdoor lighting or power lines of the distribution box, should be installed SPD, SPD in this role is mainly to prevent high potential tampering.
(3) for the need to limit transient overvoltage to a specific level of equipment (especially information systems equipment), it is appropriate to consider the installation of this equipment before the dual function of anti-operational overvoltage and anti-induction lightning third-level SPD (generally surge absorber), its location is generally in the LPZ2 zone and its subsequent lightning protection zone interface. Suggested installation location: computer equipment, information equipment, electronic equipment and control equipment before or in the nearest outlet box.