Security unit

Abstract

The invention relates to a security unit, which comprises an outer wire end, an inner wire end, a grounding end, a signal end, a fuse link, an overvoltage protection element and an alarm device, and the fuse link and the overvoltage protection element are connected with the outer wire end and the inner wire end to form a main loop of the security unit; and an alarm device composed of a normally open alarm switch and an alarm element is connected in series between the grounding end and the signal end. The alarm switch and the fuse link are of a separated non-linkage structure. When the overvoltage protection element is overheated, the fuse link is fused to cut off the main loop, and the normally open alarm switch is triggered to be closed, so that the signal end is conducted with the grounding end through the alarm element. The normally open alarm switch and the fuse link have no linkage characteristic, response thresholds can be set according to material types and corresponding meltingpoints respectively, and it is guaranteed that the normally open alarm switch is closed to give an alarm earlier than the fuse link to cut off a main loop in an abnormal state.

Description

technical field [0001] The invention provides a security unit, relates to a circuit protection device, in particular to a circuit protection device applied in the field of communication equipment. Background technique [0002] The security unit is a circuit protection device installed on the security terminal block of the main distribution frame (MDF) of the exchange in the communication field. It is a security device to prevent personal and equipment from being damaged by overvoltage and overcurrent. In the overall line, it is between the outside line (telephone line) and the inside line (switchboard). The outside line is located in a relatively complex outdoor cable environment, which often ages and overlaps with the AC power line. The security unit is responsible for protecting the communication Protect equipment from overvoltage and overcurrent damage. [0003] The circuit schematic diagram of the existing security unit is as follows: figure 1 As shown, a and b are the...

AI Technical Summary

Problems solved by technology

However, the following four defects were found in the application: 1. The main circuit switch is a mechanical contact lapping type, and its contact resistance is directly connected to the communication main circuit. The contact condition and the capacitance and inductance effect will affect the transmission of the communication line. Under the surge test conditions required by the standard, it is very easy to cause contact welding due to unstable or large contact resistance, resulting in the inability to disconnect the main circuit, which has a great safety risk; 2. The structure is more complex, including mechanical Structures such as elastic elements, heat transfer blocks, pre-deformed movable blocks, overlapping metal sheet switches, etc., lead to instability in practical applications, and difficult production and processing; 3. The alloy block is usually a low-temperature alloy due to conditions, that is, the melting point In the range of 50°C-100°C, it cannot work in a high temperature environment; 4. The heat conduction distance is long and the response is slow. Even in the case of large discharge current, the discharge tube may fail to open before the main circuit is shut down, and the discharge tube will no longer generate heat. The main circuit is not shut down and the back-end equipment is directly subjected to abnormal high voltage and damaged

[0006] This design cancels the main circuit switch, and adopts the method of suspension protection to set an alarm open circuit single switch in the branch circuit. The contact resistance of the switch does not affect the communication main circuit, but this design still cannot avoid problems other than problem point 1, and a new Some problems, such as: 1. The overheating of the overvoltage protection element triggers an alarm open circuit single switch, which will cut off the connection between the overvoltage protection element and the ground terminal. 1. When GDT does not respond, it will withstand high pressure and continue to heat up, and even cause burning; 2. The single switch for alarming open circuit uses bimetallic strips, which is costly and will reset after the abnormality is resolved. When the main channel communication returns to normal, the alarm will also be released , It is not conducive for maintenance personnel to find and remove hidden dangers in the line

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