There are many similarities between lightning protection of radio and television shared antenna systems and cable television systems and microwave systems. For example, the requirements for lightning protection of antenna feeders and lightning protection of transmission signal cables are basically the same. Only the signal cables of television systems are subject to Streets and lanes are visited by thousands of households, and some of their body and details have to be explained. At present, wireless TVs use a common receiving device, so it is in fact consistent with the cable television system in lightning protection technology.
The damage of the television system except the antenna and the part directly connected to the antenna will be damaged by direct lightning. The other lightning damage mainly comes from the lightning wave of the transmission line and the power line. Therefore, from the perspective of equipment lightning protection, it must be from the signal transmission line and the power line. Blocked mine damage. From the point of view of lightning invading people, the ground potential is mainly caused by direct lightning. The high potential is transmitted from the ground terminal to the feeder and the overvoltage is caused by the induction. Therefore, do a good job of equipment lightning protection and the correct choice and installation of lightning protection device, is a key measure to do a good job of television system lightning protection. The following lightning protection lightning respectively introduce a variety of body practices.
1. Lightning protection measures for radio towers and equipment
Equipment used for broadcasting, television and communications. Its transmitting and receiving antennas are often placed on high towers. They are more exposed to lightning strikes. So the antenna is often the target of lightning strikes. But most metal antennas have their own Protection performance, even with microwave dish antennas, horn antennas, and satellite ground station antennas, will not be damaged by lightning as long as there is a good electrical connection to their metal grounding bracket. Such as folding symmetry vibrator. To give lightning from the structure in the antenna element and the coaxial cable shield to provide a short circuit, let the lightning current directly to human safety.
As mentioned before, most microwave towers are themselves a tower of steel structure. No special protection is required except for the bottom of the tower to be properly grounded. However, all metal jackets for waveguides, coaxial cables, and other cables must have a good electrical connection between the top of the tower and the tower, and must be repetitively electrically connected at about every 30 m to ensure a balanced voltage. Broadcast transmission towers usually use pull-wires. Care should be taken to ensure that the pull-wire fixing points are not damaged, and that their skin metal is welded to the rebar, and then bolted.
The radio equipment in the tower must be equipotentially connected to many points of the tower body, which is a necessary guarantee for personal and equipment safety.
The best grounding structure for a radio station is to place a closed equalization grounding device around the foundation of a building or tower, because such a grounding device not only facilitates the connection of points, but also makes it possible to achieve potential equalization within the closed loop.
Radio towers are often built on top of the mountain. Where the foundation is often rock, it is not only costly to achieve low grounding resistance, but also difficult; in this case, the grounding limit must be made lower than necessary, and more important It is necessary to ensure that all telephones, power cables, metal jackets, waveguides into the building, tower legs, neutral conductors of power transformers, and all external metal conduits have good equipotential bonding. In this case, it should be noted that when the lightning hits the tower, the potential of the tower itself increases, and it is possible to form a very high step voltage and contact voltage. For this purpose, measures must be taken to prevent contact voltage and step voltage. The equipotential bonding is the best way to prevent step voltage and contact voltage.
3, lightning protection of signal feeders
1. The coaxial cable led along the antenna vertical bar (shelf) should be double-shielded cable or single-shielded cable should be led through the metal pipe. The outer shield metal film or metal pipe of the double-shielded cable should be vertical and horizontal. Rod and ground network for a good electrical connection. And between the cable core and the shielding layer should be installed appropriate Shenzhen Lei Zhenzi lightning arrester.
Antenna amplifier installed near the antenna, if a separate power line is used to feed power, the power cable should be laid separately through the metal pipe. Both ends of the metal pipe must be reliably grounded. The phase line of the feeder must be installed with a thunderstorm sub-protector. The zero line of the power cord should be well connected with the outer metal shield of the coaxial cable or the threaded metal tube so that the signal system and the power supply system can achieve a common zero potential. It is forbidden to use an ordinary wire for overhead application.
2. Both ends of the overhead cable hanging wire and the metal pipe in the overhead cable line should be grounded. Aerial cable lines in the outskirts of the wilderness should be grounded at the input end of each intermediate amplifier at the branch pole, the upper pole, the terminal pole, the pole for installing the antenna amplifier, and every 5-10 poles of the straight line. Both the signal source and the power supply should be connected to the appropriate lightning protection device. Ground the lightning protector at the same point as the cable shield.
3. Outdoor power lines that supply power to the system equipment or user equipment from outside. Lightning surge arresters should be connected when the power line is introduced into a building.
4. When the buried cable enters the building, the shield of the outer metal of the cable should be grounded near where the cable enters the building.
5. When the aerial cable is directly introduced and the overhead metal pipe enters the user, it should be electrically connected with the grounding device.
6. The electrical equipment grounding device and buried metal pipe in the system shall be electrically connected with the lightning protection grounding device. If they are not connected, they shall be separated by not less than 3 m.
7. Do not lay cables directly between the roofs of two buildings to prevent direct lightning strikes. The cables should be lowered along the wall to within the scope of protection against direct lightning strikes and shall not interfere with the operation of the vehicle. Its hanging wire (metal wire) should be well grounded.
8. All TV receivers shall be equipped with Lei Zhenzi TV signal lightning protection device and electronic equipment power supply special power supply lightning protection module. The lightning protection current is transmitted from the signal transmission line and the power W line and is damaged.
9. The camera should be powered by the isolation transformer in the monitoring room. The remote camera can be powered nearby, but the device should have a lightning arrester in addition to switches, fuses, and voltage regulators.
