Internal lightning protection system

The lightning protection project built and applied to the interior of a building is called an internal mine protection project. Internal lightning protection projects mainly include shielding, lightning protection devices and equipotential bonding. The internal lightning protection projects in buildings involve a wide range of facets and face many damages including induced lightning, ball lightning, conductive lightning, or power line fluctuations caused by high voltage surges on the line. High voltage introduction.

The introduction of high voltage refers to the lightning damage caused by lightning high voltage guided through the metal wire to other places and indoor. There are three kinds of high-voltage-introduced power supplies: one is that the direct lightning hits the metal wire directly, so that the high-voltage lightning propagates along the two sides of the wire in the form of waves and is introduced into the room; the second is a high-voltage pulse from the induced lightning, that is, due to thunderstorms. The discharge of clouds to the earth; or the electrostatic induction and electromagnetic induction formed by rapid discharges between thunderclouds, induce a counterattack of several kv to several tens of kv to hundreds of kV, and this counterattack will follow the neutral line of the power system, and the protective earth Lines and ground wires of various forms, either in the form of waves, propagate into the room or spread to larger indoor areas, causing large areas of harm.

Lightning strikes electronic equipment and damage mechanisms

There are three ways in which lightning strikes electronic devices by lightning strikes on electronic devices:

(I) Lightning directly hits electronic equipment network equipment

The thunder and lightning point is the high voltage side of the power supply. Lightning strikes the power supply part of the electronic equipment system along the power supply line, causing over-current and over-voltage to cause the power supply system of the power supply system to be damaged, cut off, and cause damage to the entire system.

Thunder strikes the antenna of the network wireless communication, enters the network system along the aerial feeder, cause the main communication apparatus such as communication interface, receiving system, indoor unit, router,etc. to damage.

Lightning strikes network communication wire lines (such as fiber optic cable, ddn, frame relay, x.25 private line, and telephone line) to generate strong mechanical force, violent shock wave, and hot high temperature makes communication lines

Damage; over-voltage and over-current intrusion into the network system along the communication wireline, causing damage to routers, switches, and front-end equipment.

(B) induced overvoltage

1. Loop induced overvoltage

Because the network system extensively arranges various conductor lines (such as power lines, data communication lines, and antenna feeders) in the buildings, the layout of these line networks is intricate and complicated, and many loops are formed in different spatial positions inside the building when the buildings are Lightning strikes or lightning discharges in nearby areas will generate a pulsed transient magnetic field in the interior space of the building. After this rapidly changing magnetic field crosses these loops, a transient overvoltage will be induced in the loop, which will endanger the connection with this loop. Electronic equipment.

2. Line induced overvoltage

It is the over-voltage on the network communication line, sub-static induction and electromagnetic induction

1) Electrostatic induction mainly refers to the overhead line is located near the point of lightning strike, and is charged by the lead channel of the Thundercloud group. Electrostatic induction on the overhead line accumulates a large number of opposite charges. When the main discharge of thundercloud begins, the charge velocity in the thundercloud is neutralized. As a result, the originally bound charge on the overhead line is quickly released to form a transient overvoltage wave. This wave travels near the speed of light to the overhead line and propagates. The intrusion of the network equipment terminated by the pilot line will damage it.

2) When lightning strikes directly on lightning rods and lightning protection strips, due to the large amplitude of the lightning current and the high steepness of the wave head, a strong induced electromagnetic field is formed near the channel of the lightning current. This powerful induced electromagnetic field will be directly induced on the power line or network communication equipment, forming an inductive overvoltage intrusion into the network system and damaging the network equipment. The high-intensity (30ka lightning current) lightning discharge can generate electromagnetic induction on the network system within a range of 1km from the lightning strike, resulting in damage to the system equipment. According to statistics, this induced lightning strike accounts for more than 70% of computer lightning strikes.

3. Coupling and transfer overvoltage

Lightning strikes that cause transient high voltages or overvoltages can often be coupled or transferred to a network device via a network line, causing damage to the device.

(c) Lightning strikes ground potential to increase invasion

When a building is subjected to a direct lightning strike, the lightning current will enter the ground along the down conductors and the grounding body in the lightning protection system of the building. During this process, the lightning current will generate a transient high voltage in the lightning protection system. The insulation distance between the line and the surrounding network equipment is not enough and the equipment and the lightning protection system are not common ground. High voltage will appear between the two, and discharge breakdown will occur, resulting in serious network equipment damage and even personal safety. This kind of counterattack due to improper handling of grounding technology caused ground potential and caused all network system equipment to be destroyed. The transient high potential of the ground potential endangers the network equipment in the adjacent buildings. If the network system building is not struck by lightning and no overvoltage protection measures are taken, and nearby buildings are struck by lightning, the transient high potential will be transmitted along the underground pipeline to the network. The counterattack to the line in the equipment grounding system causes the equipment connected to these lines to be damaged by the transient high potential.

Lightning overvoltage

Whether it is a lightning shock wave or a counter-attack of the ground potential, an instantaneous lightning overvoltage is generated on the network, line or equipment. Lightning overvoltage is divided into vertical overvoltage and lateral overvoltage.

1, vertical overvoltage:

The over-voltage to ground that occurs at some point in the balance circuit is called vertical overvoltage. The voltage from which the ground potential rises can be regarded as the longitudinal overvoltage that intrudes from the ground system.

2, lateral overvoltage:

The overvoltage that appears between the balanced circuit line and the line, or the line-to-ground of the unbalanced circuit, is called a lateral overvoltage. Devices that connect symmetric balanced transmission lines can cause horizontal overvoltage because the vertical overvoltage of two lines in the line is unbalanced, or because of the difference in the operation time of the vertical protection elements.

For electronic equipment connected to a coaxial cable system, vertical overvoltage is a lateral overvoltage.

Damage mechanism of electronic equipment

Damage to the equipment components in the balance circuit due to longitudinal impact includes: damage to the components or insulating medium that straddle between the line and the ground; breakdown of transformers, interlayers, or pairs of wires that breaks through impedance matching between the line and the equipment Insulation and so on. Lateral impact can be transmitted in the circuit as well as information, damaging the internal circuit's capacitance, inductance, and solid components with poor resistance to impact.

The extent to which the components of the equipment are damaged by lightning strikes depends on the level of insulation and the strength of the impact. For insulation with self-healing capability, the breakdown is only temporary. Once the impact disappears, the insulation is quickly recovered. Some non-self-recovering insulation media will not immediately interrupt the device if only a small current flows after breakdown. The operation of the device, but over time, the component parts are dampened, their insulation is gradually reduced, the circuit characteristics are deteriorated, and finally the circuit is interrupted.

Some device components such as transistor collector and emitter or emitter and base have permanent damage in the event of reverse breakdown. For components susceptible to energy damage, the degree of damage depends mainly on the flow through The current and duration on it.

Lightning strike electromagnetic pulse protection measures

(1) The building passes the main steel bar of the building, the upper end is connected with the air-termination device, and the lower end is connected with the ground network. The middle is connected with the pressure-equalizing mesh or the equalizing pressure band in each layer, and the equalizing potential is applied to the various metal pipelines entering the building. Connection, different ground lines with special requirements for equipotential processing.

(2) Requirements for wiring and grounding of computer communication network systems in building buildings: The deployment of communication cables and ground wires should be concentrated as far as possible in the middle of buildings. 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.

(3) According to the requirements of the lightning protection zone, 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. 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 screen layer consisting 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.

(4) The power lines and communication lines entering the building should be connected to the lpz0 and lpz1, lpz1 and lpz2 areas, and the front end of the terminal equipment. The power supply type spd and the communication should be installed according to the iec1312- lightning electromagnetic pulse protection standard. Network class spd (transient overvoltage protector). Spd is an effective means to protect electronic equipment from lightning surges and other interference caused by the risk of conductive surge voltage.