Lightning protection grounding is divided into two concepts. One is lightning protection to prevent damage caused by lightning strikes; the other is grounding, which guarantees the normal operation and personal safety of electrical equipment and adopts a measure of power consumption. The grounding device is the general name of the grounding body and the grounding wire. Its role is to introduce the lightning current into the ground. The protection of the lightning protection system is largely related to this. The characteristics of the grounding project itself determine the influence of the surrounding environment on the project's effectiveness. It is not feasible to design the grounding project without the specific conditions of the project site. Practice requires a systematic grounding theory to guide the actual project. The merits of the design depend on comprehensive consideration of many factors in the local soil environment. The factors such as soil resistivity, soil structure, water content, and workable area determine the choice of the shape, size, and process material of the grounding grid. Therefore, when designing the artificial grounding body, accurate design should be carried out as far as possible according to the geology of soil resistivity, soil layer distribution, etc. in the location of the ground network. Grounding body: also known as the grounding pole, is a metal conductor or conductor group that is in direct contact with the soil. Divided into artificial grounding body and natural body. The grounding body serves as a conductor that is in close contact with the soil of the earth and provides an electrical connection with the earth, and safely dissipates the energy of the lightning into the earth.
Design Principles
The grounding of communication lines and communication machinery is designed for lightning protection, high power, electromagnetic induction, corrosion prevention, and communication interference, as well as normal operation of communication and protection of personal safety.
Various grounding systems in the communications room (including joint grounding, protective grounding, lightning protection grounding, and various natural grounding bodies, etc.) can be set in two ways (that is, split mode and joint mode), but only one setting is allowed at each location. the way.
Introduce the AC power cord of the power supply room, and install corresponding low-voltage lightning arresters and equipments to protect lateral voltage in the outdoors.
Grounding body (including lightning protection, repeated grounding of AC neutral line, protective grounding, joint grounding, cable metal outer sheath, and various natural grounding bodies, etc.), connection of underground lead wires and bare conductors on the ground, etc. Electrochemical corrosion measures:
1 The grounding body (including the underground lead wire) should use galvanized steel, cast steel, copper or graphite electrodes;
2 Reduce the DC operating current of the joint grounding system;
3 The protective earthing system should have no direct current or alternating current;
4 The introduction cable should use the insulated outer sheathed cable or the metal outer sheath of the cable and the indoor grounding system plus insulation measures;
5 When two kinds of different metal wires (or metal rows) are connected, they should be welded as far as possible to ensure no false welding or false welding. When using fasteners, the joints should be tin-plated.
The lead of the grounding body must not be protected by steel pipes and insulation measures should be taken.
When using separate grounding methods, you should do:
1 The distance between various underground grounding bodies and underground bare leads shall be >20m, and grounding piles shall be installed at the locations where grounding devices are buried.
2 The protective ground bar and the joint ground bar should be installed separately in the power supply room. 3 The space distance between the outdoor lead wire of the grounding system and the house lightning discharge line: When the height of the house is 30m or less, it should generally be >2m.
The joint grounding system shall be connected to the joint ground row according to the mechanical room classification, and the connection location is as follows:
1 One pole of various DC power bus bars to be grounded;
2 introduction of racks, test racks, introduction of test racks, test benches, test bench test sites, and test instrument grounding;
3 The metal racks that do not connect to the AC power supply in each mechanical room (the DC distribution screen rack in the power supply room should not be grounded);
4 Telegraph machinery and automatic telephone repeater work grounds;
5 Insulated metal sheath for cable introduction, metal shield for distribution cable;
6 Security lightning arresters (including discharge gaps, surge arresters, etc.) in each communication mechanical room;
7 Disk shelves that are prone to noise interference are individually grounded.
The protective grounding system is connected to the protective grounding strip according to the equipment. The connection locations are as follows:
1 AC switchboards, rectifiers, other AC power supplies, and racks and chassis that access AC power;
2 The metal sheath of the AC power cord;
3 Neutral repeat grounding of AC three-phase four-wire distribution system. It is forbidden to replace the protective grounding with the neutral three-phase, four-wire system.
The following requirements shall be fulfilled when using the joint grounding system:
1 The joint grounding body, the protective earthing body, the house lightning protection earthing body, the underground cable metal outer sheath, the concrete electrode and the metal water pipe should be connected to a grounding system, and the welding and anti-corrosion measures should be taken;
2 All communication lines should be introduced underground cable, and lightning protection equipment should be installed;
3 Do not make use of the metal parts of the indoor communication equipment to constitute a lightning current leakage path.
Communication cable from the equipment room to the back row.
Copper cores should not be <35mm2 (main distribution frame to ground row); copper cores should not be <16mm2 (required for grounding resistance <10ohm for communication equipment); copper cores should not <10mm2 (requirements for grounding resistance ≥ 10Ω for communication equipment Use); aluminum core should not be <25mm2 (for industrial frequency AC equipment).
Room lightning protection construction method
There are three ways for lightning to enter the communications room:
The first is that the direct lightning strikes the metal wire directly, so that the high voltage lightning wave propagates along the two sides of the wire in a wave form and is introduced into the room;
The second is a high-voltage pulse from an induced lightning, that is, due to the thunderstorm cloud discharge to the earth;
The third type is the electrostatic induction and electromagnetic induction formed by the rapid discharge between thunderstorm clouds. This counterattack will go along the neutral line of the power system, protect the grounding wire and various forms of ground wires, and transmit the waves into the room.
The building passes the main steel bar of the building, the upper end is connected with the air-termination device, the lower end is connected with the ground network, and the middle is connected with the pressure-equalizing net or the equalizing pressure belt of each layer, and the pressure-equalizing connection is applied to the various metal pipelines entering the building. Special requirements of various ground lines for equipotential processing.
Requirements for wiring and grounding of communication network systems in building buildings: The distribution of communication cables and ground wires should be concentrated as far as possible in the middle of the building. The layout of communication cable troughs and grounding troughs should be avoided as close as possible to the columns or beams of the building and keep a long distance from them. The design of communication cable troughs and ground troughs should be located as far as possible from the building. The position of the column or beam is far away.
According to the requirements for the division of lightning protection areas, the exterior of the building is a direct lightning strike area; the interior of the building and the location of the computer room are non-exposed areas, and the more inside, the lower the degree of danger. Lightning overvoltage damage to internal electronic equipment is mainly introduced along the line. The interface of the protected area is formed by a shielding layer composed of an external lightning protection system, reinforced concrete of the building, and a metal shell. Metal components such as electrical passages and metal pipes must be equipotentially connected at each crossing point when passing through the lightning protection zones at all levels.
The power lines and communication lines entering the building shall be at the junction of LPZ0 and LPZ1, LPZ1 and LPZ2, and the front end of the terminal equipment. According to IEC1312, the lightning electromagnetic pulse protection standard, the power supply SPD and the communication network SPD shall be installed. (Transient overvoltage protector). The SPD is an effective means to protect electronic equipment from lightning surges and other disturbances that may cause overvoltage surges.
Communication equipment room grounding device construction method
Communication room grounding resistance standard, sharing a set of grounding devices, grounding resistance value should be ≤ 1Ω.
When safety protection grounding, DC working grounding, and lightning protection grounding are separately provided, the grounding resistance shall meet the following requirements: 1 Safety protection grounding, grounding resistance shall not be >10Ω;
2 DC work ground, grounding resistance should not> 4Ω;
3 lightning protection grounding, grounding resistance should not> 10Ω.
Angle steel 50 × 50 × 5mm, length 1.5m ~ 2.5m; angle steel and angle steel connection flat steel, spacing ≥ 4 ~ 5m, angle steel ≥ 40 × 4mm; lead using 50mm2 stranded copper core insulated wire or according to design requirements; The connection between the lead and the flat steel is welded, and the welding point needs to be treated with anti-corrosion treatment; the distance from the grounding body to the communication equipment room is 15m to 50m; the depth of the grounding body is 1m; and the grounding in the corrosion zone needs anti-corrosion measures.
The communication room should be based on the principle of equalization and equal potential, and a joint grounding grid should be formed between the working site, protection site and lightning protection site.
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