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Daily Maintenance of Electric Cable

Views:102     Author:Site Editor     Publish Time: 2019-08-30      Origin:Site


The basic task of daily maintenance of cable wires is to meet the needs of power grid and users for uninterrupted power supply, to prevent all kinds of cable accidents, and to ensure the safe power supply of cable lines. Let me introduce why the cable should be maintained and the contents of daily maintenance of the cable.


 

Why do electric cables need maintenance?


Because the length of cable life depends on the quality of the cable and the environment in which the cable is installed. The cable is mainly insulated by an outer covering. Over a long period of time, the insulation performance gradually decreases due to the corrosion of corrosive gases. It slowly ages and hardens, then crisps or falls off. It is dangerous for cables to lose their insulating properties. If two cables collide or fire wires touch something connected with the earth, electricity running will occur, which will raise the temperature of local wires. It generates sparks and causes fire.


In terms of cable characteristics, its shielding effect depends on its transfer impedance and insulation strength of insulating layer medium. Therefore, experts recommend lightning protection cables with small transfer impedance.


In order to reduce the damage of underground cable caused by direct lightning strike and induced current caused by lightning electromagnetic induction on cable skin, two grounding metal conductors parallel to the cable can be laid about 30 cm above the underground cable.


The underground shielded cables used in our country usually use galvanized steel wires with a cross-section of not less than 50 mm2. Their working principle is similar to that of lighting arrester above overhead transmission lines.


In order to realize cable earthing device, lightning protection grounding device should be installed. The cable line should be grounded at a certain distance, and the lead-down line is vertical to the cable. Once lightning strikes, lightning current can be safely discharged into the ground.

 


Main Contents of Cable Maintenance


Load Monitoring


The monitoring of cable load can grasp the variation of cable load. It controls the cable line in principle without overload and analyses the operation status of the cable line. Owing to the great harm of overload to cables, the load of cables should be measured and monitored frequently. The load of cable line can be measured by clamp ammeter to keep the cable line running under the allowable continuous current.


In order to prevent premature aging of cable insulation, the line voltage should not be too high. Generally, it should not exceed 15% of the rated voltage of the cable. 



Temperature Monitoring


Cable line operation will be affected by environmental conditions and heat dissipation conditions. In addition, there will be temperature rise in the early stage of cable line failure. Therefore, it is necessary to monitor the temperature of the cable line.


Various instruments are used to measure the temperature of cable line skin, cable joint and other parts. The purpose is to prevent cable insulation from exceeding the allowable maximum temperature, shorten cable life and prevent cable accidents in advance.

 

The measurement of cable temperature should be carried out in summer or when the cable load is maximum, and the line segments with the closest arrangement of cables or the worst heat dissipation conditions and the influence of external heat sources should be selected. When measuring the temperature of buried cable, the temperature of satellite soil should be measured. The distance between the installation point of the thermocouple thermometer for measuring soil temperature and the cable is not less than 3m.


The new cold end of the cable should be tracked and inspected by an infrared temperature tester. Arrange personnel to tighten the conductive connection during power outage maintenance. Because the connection of the cold end of the cable relies on mechanical pressure such as double-ended screw to connect the conductive contact surface. Workload current and fault short-circuit current are all transferred by pressure junction, thermal expansion, cooling and electromagnetic vibration may cause poor contact.

 


Corrosion Monitoring


Cable corrosion generally refers to the corrosion of metal lead or aluminum cladding of cable, which can be divided into chemical corrosion and electrolytic corrosion.

 

Chemical decomposition is generally caused by the presence of acid-base solutions, chlorides, organic humus and slag in the soil near the cable line. The main cause of electrolytic corrosion is the stray current of the DC tram track or the electric railway flowing to the earth.

 

The operation of the power grid can not be separated from the support of cables. As an important part of the power system, cables undertake the tasks of transportation and distribution of electric energy. At present, the power cable network also plays a very important role. There are many factors affecting the use of power cables, and some common faults are easy to occur. Therefore, it is necessary to do a good job in the maintenance of power cables to reduce the occurrence of cable faults. 



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