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Discuss the harm and protective measures of lightning to ele

The following in view of their respective characteristics, specific measures to talk about lightning protection.
       1. Prevent direct lightning As a result of the mining area of electronic truck scale many open areas, there are few high-rise buildings around, or not in the protection of the lightning protection system of high-rise buildings, it is possible to produce electrical discharge with the air between the clouds, the generation of direct lightning strike. For this reason, reliable measures must be taken to prevent lightning damage in areas prone to lightning disturbance. Therefore, lightning rods can be reasonably set according to specific locations and regulations to neutralize the charge in the cloud with the tip discharge effect, effectively protecting the electronic weighing system and avoiding direct lightning strike. < br / > Direct lightning lightning protection equipment is the role of lightning, that is, to prevent lightning directly hit the measuring room and lightning lightning protection within the scope of various metal pipelines and electrical equipment. It cannot protect all kinds of metal wires outside the protection range of the lightning receiver and the induced lightning generated by direct lightning. 2>. Lightning protection
        When the lightning discharge path does not pass through the lightning protection device, the discharge process produces a strong transient electromagnetic field in the nearby conductor induction of a strong electromagnetic pulse, known as induced lightning. Induction ray can invade the conductor by two different induction modes: electrostatic induction and electromagnetic induction.
    2.1Anti-static induction of lightning strike During a thunderstorm, although there is no direct lightning strike between the charged cloud in the sky and the outdoor weighing platform, electrostatic coupling can make the equipment carry charges with opposite polarity to the cloud. When airborne charged clouds and other clouds produce lightning discharge, suddenly disappear, in order to evacuate the large amount of charge gathered at the top of the scale, will produce a large backflow current. An electronic truck scale generally has 10 to 12 supporting points and sensor connection, when electrostatic induction lightning strikes caused by large current backflow, the above load point is the bad link of backflow channel, will form electrostatic induction in the circuit. Therefore, must be on the sensor, the bottom (such as bridge type weighing sensor) or left and right side), such as cantilever beam sensors set large current bypass cable, which adopts a strand woven wire jumper, make whole sensor of equipotential state formation, base plate and bearing connected to a equipotential body, to prevent accidental electric current through the sensor damage caused from the sensor. Such, scale platform and electronic car scale have large current backflow channel between the ground network, when electrostatic induction, can supplement from the earth electron, make among them and, do not because of equipment generation high potential cannot be evacuated quickly. 2.2 Protection against electromagnetic shock
In recent years, it is more the electromagnetic effect of lightning that produces a destructive surge current for precision electronic equipment.
        (1) generation of electric surge. Surge is an abnormally large current pulse at the order of microsecond, and its wave head time is generally 0.25 ~ 20&mu. S, its unit energy is generally 2.5 ~ 10MJ/Ω , which can damage electronic equipment by instantaneous overvoltage. And lightning is one of the most obvious cause of the surge, when air lightning, with a strong discharge with the opposite sex between charge cloud, will produce electromagnetic field amplitude and rise along the steep, the high strength of tem field on electromagnetic sites involved in the conductor causes a lot of induction electromotive force, so that the weighing instrument, computer host and monitor the damage of components. Therefore, lightning through the impact of hitting the power line, signal line and lightning electromagnetic pulse generated by the surge, can make computers, instruments and other electronic equipment by instantaneous overvoltage and be destroyed. In addition, large motor equipment, elevators, generators, air conditioners, refrigeration equipment, etc., will also cause surge. UPS can also be knocked out by surges.
        (2) surge protection principle. At present, in the protection of surge, surge protector has been used more and more frequently. The Surge protection Device (SPD) is a Device that shall contain at least one nonlinear voltage limiting element for limiting transient overvoltages and diverting inrush currents. General surge protectors use MOV (metal oxide semiconductor rheostat) technology, which is different from spark gap technology. The surge cannot be stopped because it contains too much energy. It is for this reason that the strategy to protect sensitive electrical equipment from surge damage is to divert the surge away from the equipment. When the voltage rises to the level set at the top, the MOV immediately ACTS, and the response time is 1-3 nanoseconds. In the MOV & other; V” It is a rheostat. At the moment of response, the resistance of MOV drops from the full value to almost zero ohm. MOV makes the transient high voltage find the access to the ground and attracts over current away from sensitive electrical equipment.
        Surge protectors are divided into three categories according to their working principle. (a) Voltage SPD(Voltage switching tspdypeSPD) switching mode is used for Voltage surge protection. Discharge gap, gas-filled discharge tube, thyratron and tri-terminal bi-directional thyristor are commonly used as components of this SPD. This type of SPD is sometimes called the SPD. Short circuit switching mode ” Or & other Kroba type ” The SPD. (b) type pressure limiting the SPD (Voltage limiting typeSPD), without electricity pour out at the moment, as the high impedance, with the increase of transient current and Voltage, impedance with continuous smaller. Varistors and suppression diodes are commonly used as components of this SPD. This type of SPD is sometimes called the SPD. Clamp pressure type & throughout; The SPD. (c) Combinatino typeSPD, a combination of voltage switching and voltage limiting components, can display either voltage switching or voltage limiting characteristics, depending on the voltage applied. According to the function of surge protector in electronic information system, it can be divided into power surge protector, antenna feeder surge protector and signal surge protector. (3) selection of surge protector. When selecting surge protectors, a manufacturer with advanced technology should be selected. The products should have detailed specifications, technical indicators, origin, standard certificates in accordance with all aspects and sales license certificates, etc.
        1) whether the design is user-friendly and easy to install. The ideal product should be small, compact, and able to be installed in an existing space while being easy to install. Therefore, when installing surge protector, the closer it is to the distribution box, the better, preferably within 15cm.
        2) reaction time. The response time of the surge protector must be faster than the surge speed. The reaction time in nanoseconds meets the technical requirements.
        3) the maximum current that can be processed at a time. The maximum current, or peak current, is the capacity of a surge protector to handle the maximum current.
        4) the ability to absorb energy. The capacity of a surge protector to absorb energy is measured in joules. The higher the joule, the longer the life of the surge protector.
        5) the ability to clamp down on voltage. That is, the ability to clamp over voltage into the safe range of electrical equipment. Launched on 1 June 1998. The 1998 standard stipulates that the clamping voltage of computer lightning protection guards (surge protectors) for 220/380v power systems shall be less than or equal to 2kV.

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