What to do if the cable fails?
Cable underground construction is the direction of urban modernization. With the increasing number of cable lines and the increase in operating years, cable faults are also gradually increasing. The faults of cable bodies, cable accessories, cable ancillary equipment, etc. that occur during cable operation are also significantly increasing. According to the author's many years of operation and maintenance practice, the cable faults mainly occur in the insulation, accessories and outer sheath.
The first is the analysis of insulation failure. The insulation aging of the cable mainly occurs in the later period of operation, generally occurring in cable lines that have been in operation for 15 years or more, resulting in a significant increase in the cable failure rate. Overheating can also accelerate insulation aging and deterioration. The electrical ionization generated by the air gap inside the cable insulation can cause local overheating, carbonize the insulation material, and cause a decrease in insulation strength.
The main reasons for insulation aging are:
(1) Improper cable selection, resulting in long-term operation of the cable under overvoltage;
(2) The cable line is close to a heat source, causing the cable to be partially or entirely heated for a long time and aging prematurely;
(3) The cable is aged prematurely in an environment that can react chemically with the insulation;
(4) When multiple cables are running in parallel, one or several of them have poor contact, causing other cables in parallel to operate overloaded;
(5) When making cable accessories, the cable connection pipe is not crimped firmly, resulting in increased contact resistance and overheating.
2. Accessory problems
The cable intermediate joints and terminal heads are usually completed on-site by the installers at the laying site, and it is easy to make mistakes if you are not careful. Cable accessory failures account for the majority of cable line failures, and their macroscopic manifestations are mainly composite interface discharge and accessory material aging. Cable accessory failures are often caused by poor manufacturing processes and carelessness of personnel. During the manufacturing process, defects such as bubbles, moisture, and impurities appear inside the accessories, resulting in local discharge and insulation breakdown.
3. Outer sheath problem
In medium and high voltage power grids, cables are increasingly widely used. The outer sheath of power cables is the first line of defense to protect the cables. Its integrity is directly related to the safety of the internal structure and the service life of the cables.
From the analysis of the causes of insulation, accessories and outer sheath failures, it can be seen that the cable line project is a systematic project. Only by managing the entire process from the aspects of design, construction, operation and maintenance can its safe operation be guaranteed to the maximum extent.
(1) It is necessary to select cables that meet their voltage levels to avoid the cables working under long-term overvoltage conditions. The selection of the outer sheath should meet the requirements of the use environment and service life. At the same time, the selection of the cable sheath protector should meet the principle that when the cable is grounded relative to the ground, the protector can reliably pass the grounding current without damage.
(2) The cable path selection should avoid the cable being affected by external environmental factors such as overheating, corrosion, and external force damage. At the same time, it should also avoid the cable being laid too concentratedly, resulting in heat not being able to dissipate in time, and causing internal factors such as overheating.
(3) Strengthen the selection of cables and cable accessories, factory supervision, and arrival acceptance to ensure the quality level of cables and cable accessories. For components that are easily affected by moisture, they should be sealed in time after inspection to prevent moisture from affecting normal use.
(4) Strengthen personnel training, conduct necessary business qualifications and technical assessments for cable head production personnel, and hold certificates before taking up their posts.
Whether the cable line can operate safely is directly related to the safe operation of the entire power grid and the stability of the system. Only by strengthening quality control and acceptance in all aspects of cable production, transportation, laying, installation, testing, inspection, and inspection can cable failures be reduced to a minimum and the long-term safe operation of the cable line be ensured.
