Lightning protection measures for wireless radio communication solution
Lightning is a kind of natural weather phenomenon. If we don't pay attention to the protection, it will cause serious harm to people's life and property. For the wireless radio communication solution, in the solution design, especially the lightning protection design should be the most important work.
Physical characteristics of lightning
According to observation, there are about 100 lightning strokes per second on the earth. Since ancient times, thunder and lightning is a kind of natural phenomenon, which has caused certain harm to human society. Therefore, it is of great significance to seek effective protective measures.
Lightning protection measures for communication equipment
Generally speaking, there are four ways to avoid lightning stroke for buildings:
1) Dredge, that is, the charge in the thundercloud dredges the earth, so as to avoid direct lightning or induced lightning current flowing through the protected buildings or equipment, so as to protect these buildings or equipment from lightning stroke.
2) Isolation, that is, to isolate the lightning signal from the protected object so as to avoid lightning stroke.
3) Equipotential, that is to say, tower ground, working ground, public ground of buildings, etc. are at the same potential.
4) Dissipating, that is to say, releasing the opposite charge and the charge in the thundercloud to neutralize, so as to prevent the formation of lightning. According to the above four ways of lightning protection, as for the lightning protection design of a radio communication project, the main lightning protection measures are as follows:
Installation of lightning rod or lightning arrester
For most of the lightning protection facilities of communication equipment, the lightning rod is mainly installed on the communication tower. This method is economical and simple, but it should be installed in strict accordance with the following requirements.
a. the lightning rod shall be installed several meters higher than the antenna tip, and there shall be a certain interval between the lightning rod and the antenna to prevent the radiation pattern of the antenna from damaging the communication effect due to the existence of the lightning rod. The general practice is that the lightning rod becomes the main pole of the antenna tower, while the communication antenna is installed at the outer edge of the lightning rod about 1.5 wavelengths away.
b. The resistance of the DC path of the grounding wire is required to be low enough, generally 10-50 Ω. Because the lightning surge current is large, the spectrum is wide and the duration is short, the inductance must be as small as possible.
c. Flat wire or stranded wire shall not be used for the ground wire, because this kind of wire has large inductance, which is not conducive to discharging lightning current and easy to be corroded. As far as possible, use solid conductors of more than 3 mm, preferably of the same metal material.
d. In order to increase the drainage area of the ground surface, multiple grounding bodies with a certain interval can be embedded and welded with each other. For example, bury about 10 copper pipes around the building at an interval of 1 to 2 meters, and weld them.
Although it is economical and simple to install the lightning rod on the communication tower, it is difficult to be foolproof. For some important communication projects, it can be considered to install radioactive lightning arresters. Radioactive lightning arrester is one of the most advanced lightning protection devices in the world.
The key part of the radioactive lightning arrester is the radioactive source, which can emit particles continuously and ionize the surrounding air to produce a large number of electrons. Under the action of lightning field, these electrons accelerate continuously, and produce interlocking multistage ionization or avalanche ionization to the air, forming an electronic flow proportional to the electric field strength. At this time, the ionization conduction generated from the radiation source to the thundercloud will continuously neutralize and release the space charge, eliminate the existing low electric field, and reduce the possible high electric field to the low electric field, so as to effectively prevent Stop the occurrence of lightning and play a significant role in eliminating lightning. The protection area of this kind of radioactive lightning arrester is large, its radius is about 260 meters, and it is safe and reliable without harm to people.
Method of preventing induced lightning stroke
In addition to the installation of lightning rod or lightning arrester on the communication tower, attention should be paid to the elimination of induced lightning stroke. The usual method is to install lightning arrester in the wireless intercom antenna system.
The following problems should be paid attention to when installing lightning arrester in wireless radio antenna and feeder system.
First, the grounding terminal of the arrester must be reliably connected with the ground, and the grounding resistance shall not be greater than 5 Ω, otherwise the lightning protection effect will be affected.
The other is that there is a certain insertion loss of the arrester, which has a certain impact on the strength of the radio antenna radiation signal. At the same time, pay attention to the change of the standing wave ratio, which is generally required to be less than or equal to 1.5 for the antenna feeder system.
Third, when installing the communication antenna, the antenna system strut is reliably connected with the tower, and the connection resistance is equal to 0 Ω. The feeder shall be hung down from the inside of the tower and fixed with copper wire every other distance.
For important wireless radio communication solution, in addition to the installation of lightning arrester in the antenna feeder system, attention should be paid to the lightning protection of the power supply system. The general practice is to install lightning arresters in transformers and distribution rooms.
