Analysis of problems existing in the use of wire and cable

Once the cable problems will be difficult to find, deal with a large workload, endangering the safety of the system power supply. Therefore, it is very necessary to analyze all kinds of questions about power cable to prevent the occurrence of problems about the safe operation of wire and cable system.

Cause analysis of deterioration of cable middle head

There are two main manifestations: one is that the touch resistance of the center head increases gradually; The other is that the insulation resistance of the center head decreases year by year, while the leakage current increases year by year. Both of these causes can increase the temperature of the central head surface. There are many reasons for the occurrence of central head deterioration, and the main reasons are:

(1) The cable has been put into operation for too long, and the service life has reached the service life. The insulation resistance of the cable itself and the center head decreases year by year, and cannot reach the standard value of the rules.

(2) The cable is often full load operation, because the current heat effect occurs heat, resulting in high temperature of the center head, and immediately the insulation deterioration of the cable center head.

(3) The cable in operation is often subjected to the impact of large current load or short circuit current impact by electrical equipment doubt, forming the insulating layer of the center head sometimes hot and sometimes cold, temperature change frequently, and the temperature difference is large, resulting in insulation deformation brittle, and immediately the insulation deterioration of the center head.

(4) The skill of the cable center head is not in place, and the oxide film at the receiving place is not cleaned. Perhaps there is oil and dust on the hands of the operator, which sticks to the wire core joint and increases the touch resistance at the joint. In long-term operation, the gradual increase of touch resistance will cause large active power loss, and the heat of the attack is also more and more large, resulting in high temperature of the center head and accelerated insulation deterioration.

(5) In the manufacturing process of the cable center head, when heating the heat shrinkable tube, it is difficult to control the temperature and easy to burn the insulation material, so the insulation resistance is reduced. Or in the heating process, due to uneven heating, there are small cracks on the end face or due to poor sealing and moisture, etc., forming insulation resistance decreases year by year, and the leakage current increases year by year.

(6) due to the wire core connection receiving quality is not good, uneven thickness may not be very matched with the joint, etc., the formation of the touch surface is not good and bad, under the effect of high current load, the temperature at the joint is too high to accelerate the insulation aging.

Power cable problem prevention countermeasures

After the analysis of the power cable question, it can be seen that to ensure the safe and reliable operation of power cable, it is necessary to do the following operations:

(1) Establish and improve consistent quality standards and standards for cables and accessories to ensure the control of product quality;

(2) In the manufacturing skills of cable terminal head and center joint, the need for sealing and moisture proof should be emphasized;

(3) It is necessary to carry out the necessary training and assessment of talents and skills for cable laying and cable end manufacturing personnel. Personnel without corresponding talents shall not carry out cable installation construction to ensure the quality of cable installation;

(4) strengthen the supervision of construction quality, stop the construction operations that do not meet the standard, and eliminate the action of dedicating to the quality of the project in order to grab the project progress;

(5) strengthen material handling, the construction as-built drawing should be completely standard, and the central joint should indicate coordinates, joint mode and quality skill requirements, so as to facilitate operation and protection;

(6) strict test and inspection, change the construction and experiment by the same part of the completion of the production management mode;

(7) Strengthen information communication with the Municipal Administration Department to prevent damage to power cables caused by excavation and piling in other construction operations;

(8) strengthen equipment patrol, the cable head manufacturing to carry out infrared temperature measurement work, the cable marked piles, guardrail, etc., to carry out periodic protection;

(9) Contact plan power failure, cable pre-test operation.

Common problems and solutions in cable production

1. The cross-linking degree (thermal extension) is not qualified

If the crosslinking degree is not up to the standard, thermal-mechanical properties of the cable are not up to the standard and cannot meet the requirement of 90℃ working temperature.

The reasons for the unqualified cross-linking degree are as follows: first, the formula is unqualified, and the type and proportion of the matching agent are inappropriate. The formula should be adjusted to solve the problem; Two is the improper vulcanization process, such as the pressure is too low, line speed, cooling water level high factors, the solution is to first find out what is the reason, may be one, may also be several reasons exist at the same time, for reasons to be excluded.

2. Unqualified structure and appearance

(1) The thinnest point of insulation layer thickness is lower than the minimum value specified in the standard, or the average thickness is lower than the nominal value. The reasons for the unqualified insulation thickness are fast linear speed, small amount of extruder glue, improper selection of mold and so on.

The solution is to reduce the linear speed or extruder speed, adjust the size of the die.

(2) eccentric

The reason for eccentricity is that the suspension control changes after the mold is not adjusted or raised. The solution is to control the stability of the drape as far as possible in the process of driving.

3. Bamboo joints

The reason for the bamboo-shaped cable is that the traction speed is unstable due to the electrical and mechanical system, and the mold core is too small or the outer diameter of the conductor is not uniform.

Troubleshooting method is to check the mechanical, electrical system, troubleshooting. Adjust the size of the core appropriately, control the suburban outer diameter as far as possible uniform, more than the process can be used strand.

4, surface scratches

(1) The cable encounters the upper and lower wall or foreign matter in the vulcanized pipe. Therefore, it is required to adjust the suspension degree, try to make the core move in the middle of the crosslinked pipe, and clean up foreign matter in time.

(2) There are burnt objects on the outer edge of the mold sleeve. The solution is to get up when the mold sleeve temperature adjustment, to prevent overheating, once found burned, should immediately stop to clear, or not to become better.

5, impurity

Most of the impurities in insulating materials and semi-insulating materials are brought into the mixture and extruder feeding process. In the process of operation, strict attention should be paid to the cleanliness of the material to prevent external impurities from mixing. Another impurity is coke bumps, its existence affects the performance and service life of the cable, so in the mixture and extrusion strictly control the temperature, to prevent the occurrence of coke phenomenon.

6, bubble

Bubbles can develop in insulation for two reasons. One is caused during extrusion. The solution is to choose the appropriate mold. The shielding layer has bubbles, the main reason is that there is water in the material, should be dry before extrusion, and the second is insufficient cooling, then there will be as follows, a circle of bubbles on the circumference of the line core equidistant. The method of elimination is to strengthen cooling, raise water level and reduce the temperature of cooling water.