CATV system, lightning protection technology (I)
Is an atmospheric discharge phenomena, often makes cable television equipment was severely damaged in the CATV system, the lightning protection design is a very important task, which in practical engineering, mine has not caused enough attention of technical personnel, Once was struck by lightning, there is no good lightning protection measures of the system will have been seriously damaged, and even paralysis. Large-scale systems for long lines, lightning protection design is even more pressing task, this article from the generating mechanism of lightning and thunder and lightning of the distribution of lightning elaborated with a view to the reader an overall understanding of lightning, thus described the measures as well as the CATV equipment, lightning protection the anti-lightning performance.
There are two kinds of lightning: "Direct is not mine" and "lightning." Lightning directly stroke rate of only about 10% of lightning strikes, crimes against the scope of the general small, can use the lightning rod, lightning, and lightning-line network of anti-avoidance, endangering a much larger "lightning" accounted for nearly 90% of the rate of lightning strikes, against a wide range of , CATV system, electronic equipment damaged by lightning ring, mainly caused by lightning. Lightning directly stroke
Electrically charged clouds and the earth was created between the discharge, in the process of the formation of Thundercloud some clouds built up a positive charge of the Li cloud close to a certain extent, the discharge occurs very rapidly. There a bright flash. When Thundercloud is very low, around the opposite sex no charge Thundercloud, they will on the ground or the buildings out of the opposite sex charge induced to form a charged cloud to the ground or building discharge; discharge current can reach tens or even hundreds of Mochi-an , the discharge time of 50-100μ S, such a discharge is the lightning directly stroke, lightning directly stroke of buildings and people, great animal safety hazards. Installed in the lightning rod, the
CATV system, even if the electronic equipment within the scope of its protection may still be damaged by lightning, mostly burning fuses, power transformers. Rectifier component, three-terminal regulator, serious damage to integrated circuits and other components may also be, indicating the introduction of lightning strike than from the antenna, but from the introduction of the power cord, showing that although lightning rod to protect the buildings, but can not be placed on the protection CATV inside the electronic equipment, which is caused by lightning.

Induction electrostatic induction, and lightning current lightning generated electromagnetic induction caused by two kinds of reasons, when the charged clouds (Thundercloud) near the transmission lines, it will above the sensor out of the opposite sex in their charge, these charges are Thundercloud charge heterosexual fettered. When Thundercloud on nearby targets or Jieshan Qi (lightning rod is the first and most commonly used Jieshan Qi) discharge, its quick and in charge, while the transmission lines on the road bound charge will be for free charge, the formation of local high-voltage induction . This induction occurred in the low-voltage high-voltage overhead lines can also be reached when the 100KV; in telecommunications lines of up to 40-60KV.
And it can be passed along the line electronic equipment,
Damage. After the huge lightning strike lightning current in the surrounding space generate alternating magnetic field, due to electromagnetic induction sensors out of a nearby high-voltage equipment, so that equipment damage.

The distribution pattern of China's thunder and lightning is: usually hot and humid areas than in cold and dry areas of lightning and more thunder and lightning at the same time the frequency is decreasing with the geographical latitude increases, that is, closer to the equator the higher the frequency, specifically with South "Southwest" Yangtze River "North" Northeast "Northwest, in addition to the frequency with lightning changes from region to region, namely: mountain" plain "the desert, the land" and lakes every year peak of lightning in 7-8 months, the activities of mostly in the 14-22, when the time between. Whether lightning is an area determined by the weather conditions, but the specific lightning points are influenced by local conditions. ① terrain,
Usually mountain Dongpo, the southern slope is more than likely lightning Mountain West. The northern slope of the mountain in the plains, lightning probability is larger than Canyon Lake beach lightning probability is small, but the lakes, if they rely on the water side of mountain slopes are more likely to drop mine; draft, or downwind of the valley easy to lightning. ② the impact of objects on the ground, open land in the isolated groups of buildings in high-rise buildings and buildings vulnerable to lightning, the metal structure, roof, tower susceptible to lightning strikes, tree hut, receiving antennas, transmission lines are easy mountain been struck by lightning, it is because these things on the ground at the Thundercloud and the earth Geely to establish a good discharge channel. ③ the impact of geology, soil resistivity
The relative value of the accumulation of small but fast electric charge relative to the local easy to lightning, there are large areas of soil resistivity is large, the local soil resistivity of the small size of Yi lightning; soil resistivity of a small hill slopes or soil easily lightning; soil, there are conductive mineral regions Yi lightning; water table in areas of high or spa easy to lightning.

Mine the most favorable for the system of measure is a good grounding system, a good grounding not only to vent out early in the voltage generated lightning, but also leaked out due to device leakage generated ground voltage, to protect the equipment and physical security purposes, the specific system, mine is from the earth began. In the meantime, where it is needed by lightning installed, the arrester, but the use of anti-lightning equipment performance is not ignored in the selection of equipment, the examine the anti-lightning equipment performance is also an important part. At present, China's mass production and use of arrester,
Have had the electrician as the basic element silicon carbide valves of various valve-type arrester; a zinc oxide varistor to the basic components of the zinc oxide arrester, zinc oxide arrester arrester valve than with the action quickly, Flow capacity, residual depression , no freewheeling, simple structure, high reliability, long life, easy maintenance and so on. The following highlight the zinc oxide arrester, zinc oxide varistor arrester for lightning and the lightning surge intrusion prevention to be effective. The working principle of their volt-ampere characteristics of the non-linear. The normal voltage,
Arrester was high-impedance state, only a small leakage current (μA orders of magnitude), power loss is very small, when the line appears in overvoltage, the arresters showed low resistance state (time effect for the 10-9 orders of magnitude) over-voltage with discharge current form through the arrester into the earth, over-voltage was inhibited down after the surge voltage, line voltage is back to normal when the arrester also showed high resistance insulating state, so there must be a good grounding arrester device with co-arrester volt-ampere characteristics of the following diagram as follows:
Where: i a lightning discharge current: VimA a leakage current when the lmA voltage, VI a discharge voltage, Ve a lightning surge voltage.