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The monitoring system of lightning protection design, discussion

Categories: Technical SupportStars: 3Stars Visit: - Release time: 2014-04-25 20:26:00
Font size:【 Large Middle Small Source: Editor: Author:

  One, the introduction

  As the safety monitoring system in Banks, traffic, communities, the rapid popularization application of warehouse management, equipment monitoring and control system for the likelihood of lightning damage is greatly increased. The consequences may be the whole monitoring system operation failure, and is difficult to estimate the economic loss caused.

  Security monitor system in order to take effective lightning protection measures, to ensure normal and reliable operation, monitoring and control system should first clear the monitoring system of the main causes of lightning strike damage and possible lightning invasion pathways, especially the lightning damage serious outdoor surveillance equipment, on the basis of analyzing the reason for its damage, correct selection and use of monitoring and control system equipment of lightning protection devices, as well as the study and exploration of the signal and power circuit cloth, shielding and grounding method, etc. Can make the security engineering companies, to improve the electrical resistance of the monitoring system, optimize the system lightning protection level have very good effect.

  Second, composition and the formation of closed-circuit monitoring system

  1, TV monitoring system (ClosedCircaitTelevisiow, referred to as "CCTV), generally consists of three parts:

  The front part: mainly by black and white (color) cameras, lenses, yuntai, shields, support, etc.

  Transmission parts: using coaxial cable, wire, multiconductor take overhead, buried, or along the wall for laying way transmission of video, audio or control signal, etc.

  Terminal part: mainly by the image segmentation, monitor and control equipment, etc. 2, the causes of CCTV system

  Direct lightning, lightning strike on the outdoor camera directly cause equipment damage; Lightning strike on the overhead cables directly cause cable fuse.

  Thunder electric wave invasion: China central television (CCTV) power cable, signal transmission, or metal pipeline into the control room by lightning or thunder and lightning induction, thunder electric wave along the metal wires into equipment, causing potential equipment damage.

  Lightning induction: when lightning rods, around the downlead will produce strong tem field. In the electromagnetic field monitoring equipment and transmission line a lot around the electromotive force is induced. This phenomenon is called electromagnetic induction. When a charged thunder clouds appeared, buildings and transmission lines under the thundercloud charge induction out in contrast to the thundercloud. The induced charge of up to 100 kv in the low voltage overhead lines on the road, including 40-60 kv line road. This phenomenon is called the electrostatic induction. Electromagnetic induction and static electricity is called induction lightning, also called secondary ray. It is the damage to the equipment without lightning strike to suddenly, but it is much more than the chance of hitting LeiFaSheng.

  Third, China central television (CCTV) system of integrated lightning protection

  1, the front-end equipment of lightning protection

  Front-end equipment have outdoor and indoor installation two situations, installed in the indoor equipment, generally will not suffer from direct lightning stroke but should be considered to prevent lightning overvoltage on equipment, while the outdoor equipment should be considered at the same time prevent direct lightning stroke.

  Front-end equipment such as camera should be placed by ShanQi (lightning rod or other lightning conductor) effective protection scope. When the camera during erection, lightning rod best 3-4 meters distance from camera. If you have difficulty lightning rod can be set up on the camera support bar, downlead rods can be directly used in itself or choose Φ 8 galvanized round steel. To prevent electromagnetic induction, along the rod on the camera power and signal lines should wear metal shielding.

  To prevent thunder electric wave invasion along the route to the front-end equipment, should be equipped with each line of the equipment before an appropriate lightning arrester, such as the power cord (220 v or DC12V), video lines, signal lines, and yuntai control line.

  The power of the camera using AC220V or DC12V in general. Camera by dc power supply transformer, single-phase power supply arrester should be in series or parallel in front end dc transformer, such as dc power transmission distance is more than 15 meters, the camera should be concatenated low-voltage dc lightning arrester.

  Signal transmission distance is long, low pressure and easy to damage to the equipment, induction lightning current to conduct from the signal transmission line lightning current into the ground, over-voltage protector must be quick response signal, must be considered when designing the signal transmission line protection signal transmission rate and signal level, to start the parameters such as voltage and flux of the thunder and lightning.

  Outside the front end of the equipment should be good grounding, grounding resistance less than 4 Ω, high soil resistivity area can be extended to < 10 Ω.

  2, transmission line lightning protection

  CCTV system mainly transmission line and the power cord. Outside the power of the camera can be introduced from the terminal equipment, can also be introduced from near the monitoring points of the power supply.

  Control signal transmission line and the alarm signal transmission lines generally choose soft core shielding line, the erection (or installation) between the front and the end.

  GB50198-1994 rules, the route of transmission parts in the suburbs of city and country, laying of directly buried installation can be used. When conditions are not allowed, or overhead way, communication pipeline can be used as stipulated the transmission cable with other line other line its groove (see table 1), and the shortest distance between a rod with other lines set up the minimum vertical distance (see table 2)

  Table 1 cable trench with other lines (tunnel), the minimum distance (m) species minimum spacing of 0.5 220 v ac power line communications cable 0.1 table 2 cable rod with other lines set up the minimum vertical distance (m) species minimum vertical distance between 1-10 KV power line 2.51 KV powerline GuangBoXian line 0.6 1.0 1.5 below

  From the Angle of lightning protection, lightning protection effect is best, directly buried installation overhead lines is the most vulnerable to lightning strike, and the destructive, spread to a wide range, in order to avoid the first end equipment damage, aerial transport should be grounded on each pole when processing, aerial cables of messenger wire and overhead cable line are connected to the metal pipes. Intermediate amplifier at the input shall be respectively suitable access to the source and power source.

  Buried a transmission line and prevent the occurrence of lightning equipment, a large number of facts show that lightning damage of buried cables, about 30% of the total failure, even if the lightning is far away, still there will be a part of the lightning current flows into the cable. So with belt shielding layer of cables or cable wear steel pipe buried, keep steel electrical connectivity. For shielding electromagnetic interference and electromagnetic induction is very effective, this is mainly due to the metal shielding effect and skin effect of lightning current. Such as cable wear all the metal are in trouble, but in front of the cable into the terminal and front-end equipment wear metal pipe buried, buried length of not less than 15 meters, at the door end the cable metal sheath, steel pipe is connected with lightning protection grounding device.

  3, terminal equipment of lightning protection

  At a China central television (CCTV) system, the control room of the lightning protection is the most important, from direct lightning protection, thunder electric wave invasion, equipotential connection and surge protection in many aspects.

  Control room in the building should have direct lightning prevention of lightning rod, lightning protection belt or lightning protection network. The direct lightning proof measures shall be in accord with GB50057-94 regulations on lightning protection.

  Into the control room of resisting the inductive thunderbolt at various metal pipe should be received the grounding device. Aerial cable directly into, in the household should be equipped with lightning arrester, and the cable and metal outer security layer bearing wire received the grounding device.

  Control room should be set up first-class electrical connection bus (or plate), the bonding bus bar with building lightningproof grounding, PE line, equipment, sites, antistatic etc together to prevent dangerous potential difference. All kinds of surge protector, lightning arrester grounding line should be in the most direct and the shortest distance to equipotential connection bus for electrical connection.

  With 80% lightning high voltage from the power cord invasion, in order to ensure the safety of equipment, the general power supply should be set on level 3 lightning protection. In the video transmission line, the signal line, intrusion alarm signal before entering the front-end equipment or into the center console shall be equipped with corresponding lightning protector.

  A good grounding is a vital part of the lightning protection. The smaller the overvoltage grounding resistance value is lower. The monitoring center using special grounding device, the grounding resistance shall not be greater than 4 Ω. Using comprehensive grounding network, the grounding resistance shall not be greater than 1 Ω.

  Four, the conclusion

  Lightning damage to the safety monitoring system approach are manifold. This article mainly discusses the security monitoring system lightning strike damage

  Main reason, and possible intrusion ways made the preliminary analysis, for the security monitoring system lightning protection technology is introduced. To be sure, lightning protection is a complex problem, lightning protection design of safety monitoring system depends not only on the performance of the lightning protection device, what is more important in the design of monitoring system construction, consider to the geographical environment monitoring system, design the right means of wire cloth, shielding and grounding method. All in all, lightning protection design should be comprehensive consideration, can obtain good effect.