In-depth description of comprehensive lightning protection of programmable Switches

Program-controlled switches are still commonly used. So I have studied the comprehensive Lightning Protection Problem of the program-controlled switches. Here I will share it with you and hope it will be useful to you. Power Communication (Power Communication Network) is an indispensable part of modern power systems and one of the three pillars of the safe and stable operation of modern power grids, the program-controlled switch is an important part of Shaanxi Electric Power Communication Network. Once a fault occurs, the losses are not only economical, more seriously, it poses a potential threat to grid security. Therefore, it is particularly important to strengthen the security protection for the programmable switches.

The main component of a Programmable switch is an integrated circuit (IC ). The IC anti-interference capability is relatively low. Even the lightning electromagnetic pulse (LEMP) induced by the line can penetrate the IC element. Therefore, programmable switches are prone to lightning strikes. I will analyze and discuss this issue in depth.

Principles of classification and prevention of lightning disasters

Lightning strikes can generate different types of damages. The International Electrotechnical Commission has called lightning disasters a "major environmental hazard in the electronic age ", transient overvoltage, such as lightning strikes, inductive lightning strikes, and power sharp waves, has become the culprit in damaging electronic devices. From the analysis of a large number of lightning strikes on communication equipment, experts believe that lightning electromagnetic pulse LEMP caused by lightning induction and lightning wave intrusion is the main cause of communication equipment damage. To this end, we adopt the "overall defense, comprehensive management, and multi-protection" principle ". We strive to minimize the potential harm.

Main Countermeasures for Lightning Protection

Grounding is the most basic and effective measure in the lightning protection system. According to the different functions of "grounding", we can divide "Ground" into "Work Place", "Protected Area" and "Lightning Protection ground. An important communication equipment system must have a "working place". It provides a standard reference potential for the entire system. With this reference potential, the system can work normally; if the system is powered by a strong power supply at the same time, the device housing must be connected to a "Protected Area" to protect personal safety. If the system is connected to an outdoor metal equipment or cable, the system also needs to be connected to the "Lightning Protection ground" in a reasonable position to prevent lightning strikes and high voltage string from entering the system.

If the "work location", "Protected Area", and "Lightning Protection" of the communication system are separately installed, they do not connect to each other and are self-contained systems, which are called "separate Grounding System ". If the three are combined to form a unified grounding system, we call it a "combined grounding system ". Currently, the scheduling and communication building in Shaanxi Province is connected to the ground. The combined grounding system eliminates the potential difference between different grounding points. when lightning strikes occur, the discharge between different grounding points can be effectively restrained. The grounding of the programmable switch and the grounding of the whole building are very important. According to the standards and regulations of the Ministry of Information Industry, the impact Grounding Resistance of anti-lightning grounding of telecommunication buildings should not be greater than 10 ohm yd5003-94 "Code for designing telecommunication special houses"), the grounding resistance of important telecommunication buildings should be under 1 ohm ydj20-88 "interim technical provision on installation and Design of program-controlled telephone exchange equipment"). If the ground connection does not meet the requirements, when the switch is subject to strong power interference or lightning strikes, serious damage may occur. The grounding of the program-controlled switch under the jurisdiction of Shaanxi electric power company adopts the combined grounding method, and the grounding resistance of the grounding body is <1 Ω measured at 0.7 Ω ).

In the actual wiring process, a wiring similar to "scattered grounding" is adopted, that is, both the working and protected ground wires are drawn from the ground wires. The two wires are not directly connected to each other. See figure 2, its advantage is that when the lightning current flows through the grounding network, the lightning current flows only vertically, and even if there is a bad contact, it will not cause horizontal interference. Grounding treatment of the switch: A 135mm2-inch copper core wire is used to separately connect to the grounding line. Different from the system: 1) The Cabinet is not directly connected to the positive pole of the switch, nor randomly connected to the cable or wire with the positive pole. 2) The contact parts of the Cabinet, the elevated floor, and the base are insulated, equivalent to the "floating grounding" method, in order to prevent the static electricity of similar surface layer and the stray current of buildings from being stringed into the cabinet, which may interfere with communication.

Grounding of the total distribution frame: Two 50mm2 multi-strand copper core wires are separately introduced from the master line, one of which is connected to the base of the distribution frame, and the other is connected to the grounding copper strip at the top of the distribution frame. The advantages of Dual-line grounding are: on the one hand, the reliability of the security equipment and the alarm signal circuit can be improved; on the other hand, when the communication line is struck by lightning and high-voltage current and enters the ground through the security guard, it can quickly reduce the potential on the distribution frame. After the joint grounding method is adopted, the grounding of the equipment and floor is more reliable, effectively ensuring the safety of the equipment and the person.

Rational Integrated Wiring

The wiring of a program-controlled switch is a very professional task. The wiring scheme should be considered in the design phase. Cabling includes program-controlled switch trunk lines, internal lines, power supply lines, and indoor ground wires. The transmission network of a vswitch adopts two methods: overhead and overhead. For overhead cables, the telephone lines or cables should be buried before entering the room. The buried length is> 2 P (P is the resistivity of the grounding resistance, in the unit of Ω * m), and the actual length is> 50 m. Generally, metal-clad cables are directly buried, or non-metallic shielded cables are directly buried through metal pipes. From the perspective of Lightning Protection, underground cables should be used in case of conditions.

The transmission network of the programmable switch should be cabled along the dedicated signal cable trough in the room to avoid laying along the building structure column or close to the external wall. strong and weak current cables should not be laid along the same trough to reduce interference. For example, if a dispatching center building in Shaanxi does not have a special signal cable trough, its signal line and power line are laid in the same trough. When the power line is struck by lightning or lightning pulse, it will also sense an electromagnetic pulse on the signal line and transmit it to the switch along the signal line, causing the switch to be damaged by lightning strikes.

Measures for determining traffic distribution and pressure limit

Line lightning arresters should be installed in the indoor programmable telephone and dedicated data cable channels. When using lightning arresters, the start voltage should be 1.5 times of the Signal Peak voltage of the Protection line, and the lightning flow flux is greater than or equal to 0.2KA, the characteristic impedance is 600 ohm and the operating frequency is 0-5 MHZ. If a receiving device is outdoors and a signal line is connected to an indoor device, a lightning arrester of the corresponding type should be stringed between the incoming line and the device of the antenna receiving device. The above lines and the signal arresters installed on the equipment should be grounded nearby, and the grounding resistance should be less than 4 ohm. Some of them must be less than 1 ohm for special requirements on Grounding ). In addition, the grounding wire cannot be connected to the lightning rod or lightning rod. It should be connected to the grounding wire of a special Lightning Arrester and directly connected to the ground network. Installed on the power cord, signal line, commonly known as lightning arrester), lightning electromagnetic pulse attack, timely Ray current into the ground to protect. When selecting a referer, pay attention to the response time. When some security guards intrude into the thunder current, the protected device is damaged, and the security guard is still intact, because the response time is too slow. Line lightning arresters consisting of core devices, such as ZnO resistors and varistor, are now popular in the market. The response speed is faster and the effect is better.

Other effective measures

Determine the equipotential connection of the Communication Room: that is, all metal devices, external conductive materials, power lines, communication lines and other cables entering and leaving the room should be connected to the total bus to form an equipotential metal connection. The data room shall be equipped with an equipotential pressure network and be connected to the grounding system of the building. The equipotential network should adopt M-shaped network, and the DC Ground of each device is connected to the Equipotential network at the shortest distance. Principle of shielding a vswitch: In addition to signal lines and power lines, the switch room should also be shielded, the specific method is to ground metal doors, windows, ceilings and anti-static special floors. The potential distribution of each point is even, and the internal staff and equipment will be well shielded.

Conclusion

In modern communication systems, a well-designed lightning protection system is crucial to the safe operation of devices. Not only for programmable switches, but strictly follows the principle of comprehensive lightning protection, planning and protection from various possible lightning strikes can ensure the safe operation of the entire communication network.