Communications Security Equipment with tools of protection for communication project YH00

Definition
Communication line protection: various protective measures adopted to protect communication lines and equipment from damage or interference by external electromagnetic fields or other environmental factors.
Chinese name: communication line protection
Mbth: protection of tele communication line
Nickname: none
Applied disciplines: information communication
Features: electromagnetic field, environmental factors, communication lines, protective measures
Source of impact
The electromagnetic field that affects the communication line mainly comes from the following aspects:
1. strong wires: such as the high-voltage transmission lines we often see, electrical transport equipment such as the catenary of electric trains and the power supply lines of high-speed railways, etc.
2, lightning, magnetic storms, and sunspot movement of electromagnetic storms and other natural electromagnetic field source.
3. electromagnetic waves radiated by radio stations, radiotelegraph, etc.
4, the city's cable broadcasting network.
5, the industrial electromagnetic interference of industrial and mining enterprises
6. power carrier line.
7, nuclear fusion electromagnetic pulse.
8, computer, microwave oven and other household appliances leaked electromagnetic waves.
Influence of strong wires
The power supply of the strong wire is divided into two different systems:
1, strong wire in each phase of the wire current and potential amplitude is equal and the phase of the symmetrical system, such as three-phase alternating current.
2, strong electric wire using the earth ( or other track ) as a conductor of asymmetric system.
We need to understand that asymmetric systems and faulty symmetric systems have a great influence on communication lines. And the normal operation of the symmetrical system, the influence of communication line is relatively small.
The current in a strong wire is magnetically affected in a communication line by the electromagnetic mutual inductance ( coupling inductance ) between the strong wire and the communication line. And the voltage of the strong wire through the coupling capacitance between the strong wire and the communication line, will produce a movie in the communication line. These electromagnetic effects can impair the transmission quality of electrical signals. The principle of the mutual inductance phenomenon is shown in fig. 1.
Fig. 1 principle of electromagnetic mutual inductance
For the asymmetrical system of the strong electric wire, the ground current of the strong electric wire will produce different ground potential in different places of the earth, and the ground current will be affected on the communication equipment by the action of the coupling resistance.
The influence of these strong wires, heavy damage to communication equipment or endanger the life safety of operation and maintenance personnel; Light is produced in the telephone circuit noise, in the telegraph circuit distortion, reduce the quality of communication.
Effect of lightning
Lightning and thunder, the natural phenomena of communication lines will also have a significant impact. The technician classified lightning:
1. linear lightning
2. flake lightning
3. chain lightning
4, ball lightning.
Of the four lightning types mentioned above, linear lightning is the most harmful to communication lines.
The technician also classified the mine:
1. direct lightning strike: lightning strike directly on communication line equipment. Direct lightning often damages communication line equipment, causing serious harm.
2. induced lightning: lightning that does not directly hit the communication line equipment but induces voltage and current in the communication line. Induction lightning sometimes damage overhead bright line of poor quality or unclean every electron; In most cases, external equipment will not be damaged, but will cause interference in the communication equipment, affecting the quality of communication.
stray current
The following describes the effect of stray current on communication lines:
In people's production and life, current is everywhere. Such as electrical railways, high-speed rail, trams, other remote power supplies, and even ground wires for direct current transmission lines. We refer to these existing electrical flows as stray currents.
Stray currents into the ground often cause electrical erosion ( electrolytic erosion ) of the metal sheath of underground cables and optical cables. Dc erosion is more serious than AC erosion. Note the following concepts:
1 ) cathode area: the area where stray current flows from the earth into the communication line equipment.
2 ) anode area: the area where stray current flows back to earth by line equipment.
It is common for that anode region to be subject to electrolytic corrosion. Due to the different geological conditions, sometimes the cathode area will also appear electrolytic corrosion phenomenon. At the same time, the external natural environment is complex and changeable, there will also be chemical intergranular corrosion, microbial corrosion, soil corrosion, etc., which will affect the communication line. Underground cables and cables can also be " attacked" by termites, wasps and mice.
Influence of external electromagnetic field
What effect does the external electromagnetic field have on the communication line?
1, high altitude nuclear explosion will form a strong electromagnetic pulse, it not only harm to the metal cable; Some optical cables without metal components may also have an impact. It will increase the temperature of the optical fiber, which will affect the transmission loss characteristics of the optical fiber.
2. high voltage transmission line: the strong electric field generated by high voltage transmission line is an electromagnetic pollution. If there is no reasonable protection of communication line, also affect the quality of communication transmission.