First, the preface
As we all know, with the rapid development of the telecommunications industry, online operation of MDF has reached hundreds of millions of. In particular, the environment around the rural end of the perimeter cable is relatively complex, so there are often a variety of external hazards on the cable line, including the impact of the power line is the most serious. If the MDF fire accident, not only damaged and scrapped a large number of communications equipment, but also may cause communication cable damage, resulting in a great potential for communication security.
In order to ensure the safety of communication operation, the communication system generally adopts level two protection, that is, the first level protection of the total distribution frame and the two level protection of the SPC exchange program. But the core responsibility of the protection is still to be completed by the total wiring frame, so the safety protection of the total wiring frame becomes the first pass of the switch safety.
Second, MDF general wiring frame working principle
MDF total wiring frame is one of the main equipment of the local telephone measuring room, all the outside lines are connected to the total distribution frame, and then the total wiring frame is connected to the related mechanical equipment. Outside the cable is not directly connected to the switch, during which must pass a handover equipment, this is the total wiring rack.
Total wiring Frame
The basic functions of the total wiring frame are as follows:
1. With wiring function, the jumper can connect any one of the inside to the outside line.
2. A protective device that forms a protective system, along with an outside and inside of the switch, to prevent damage and damage caused by overvoltage, overcurrent, equipment and operators within an outside line.
3. A location that is tested with an internal outside line.
4. With alarm function, alarm issued can be heard, visible signals, foreign teachers can timely detect the action of the Security unit.
As the protection device of switch protection, MDF general wiring frame plays an important role in Lightning overvoltage, anti power frequency induced overvoltage and power frequency contact overcurrent. But there are also obvious weaknesses of the characteristics. In recent years, due to numerous domestic MDF manufacturers, technical level has a high and low, the corresponding in the communication stations used in the distribution and security units of various types, uneven quality, the installation and use of some products to the communication station formed a fire hazard, strong electrical intrusion caused MDF total wiring frame fire burning accidents often occur, It can be concluded that the safety of MDF general wiring frame has seriously threatened the safety of communication operation.
The biggest unsafe factor of the MDF distributor is the fire hazard, and the direct source of the fire is the strong electric intrusion and the high temperature and heat caused by it, which leads to the fire of the security unit, the security wiring platoon or the outside cable.
Since the strong electric intrusion is mainly due to the high-voltage power lines and the local telephone cable to meet, then the strong electricity intrusion, MDF security Unit of the action and the line voltage and current situation?
Analysis of the status of MDF total distribution frame
Security unit is inserted in the security wiring row to prevent personal and equipment suffered overvoltage, over-current damage of a protective device, is the main part of the total wiring rack. According to international standard "CCITTK." 20 suggestion "and our country line environment actual situation, installs in the general distribution frame the security unit must have three function, namely the lightning protection, the strong electricity induction, and the prevention AC mains function." Especially for over voltage, over current two protection capacity of the program-controlled switchboard, security unit of the first level of protection function is more important.
(1) Lightning impact: Refers to the lightning impulse generated by the surge voltage it has instantaneous and instantaneous completion of the characteristics of some voltage up to tens of thousands of volts, thousands of volts ranging, depending on the distance between the occurrence.
(2) strong electric induction: when the cable through certain special places, such as electric railways or substations or power plants, solenoid valve coils sometimes due to electromagnetic fields caused by Sensen. According to the induction current distance has long-term induction, short-term induction points, general can be summarized as follows: Long-line induction has a large voltage, the corresponding small current characteristics: Short-term induction has a large voltage current is also a big feature.
(3) Power line touch: multistage pump in the cable erection, our country's actual situation is the telephone cable and mains cable or tram cable in the air parallel or criss-crossing erection, due to wind and rain sun and lightning, animal damage, cable aging and so on, so the power line lap or more often occurs.
Above three kinds of situation enters the Bureau, the serious will cause the flame burning, burns out the wiring frame module or the Switch User circuit board. Although the MDF security unit can be foreign invasion protection, so that can play a certain role in protection and alarm function, but from a security point of view, the traditional MDF in the strong electric intrusion alarm in the practical application, there are a lot of accidents and deficiencies, here a brief analysis of the following.
Short-circuit protection may cause a large short-circuit current on the line
MDF's current design idea is to short-circuit the intrusive overvoltage over current, therefore, in a typical strong electric intrusion case, the current of its line in the beginning due to PTC limit flow and reduce, the dry cleaners joined with the Overvoltage protection device and subsequent failure protection device start-up, the line current will continue to rise, Cause the line current is quite big, may cause the line cable will appear melts adhesion and so on condition, causes the guarantee arrangement module and the security unit may also melt the deformation, at the same time very possibly because of the cable massive adhesion string, but causes many user lines to suffer from the big current invasion, causes the open fire.
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