High voltage cables are the bridge between power supply equipment and electrical equipment, playing a role in transmitting electrical energy.
The structure of high-voltage cables is composed of conductors, insulation, inner protective layer, filling material (armor), and outer insulation. In order to avoid external influences, high-voltage cables are usually buried below the ground or laid in dedicated cable trenches. The causes of faults in high-voltage cables can be roughly divided into three main reasons: manufacturer manufacturing, construction quality reasons, and external damage.
Fault cause analysis
The manufacturing reasons of the manufacturer are easy to understand, such as small defects such as small bubbles and scratches in local areas during the production process, which can generally be detected by applying a certain multiple of AC voltage resistance during the handover test.
The reason for construction quality is due to the lack of attention during installation and laying, which causes cable pulling, scratching, gravity impact and other factors, resulting in hidden dangers in high-voltage cables. Depending on the severity, it may be detected during handover tests or the carbonized insulation at the fault point may weaken after running for a period of time, ultimately leading to breakdown.
The most common high-voltage cable faults caused by external damage are mechanical strains or direct breakage. During the process of cable fault diagnosis, we found that some cables are still buried after being pulled, and the insulation level of such cables has changed due to severe tension. Over time, local moisture and partial discharge will eventually lead to cable faults.
processing method
After a cable failure, it is necessary to first know the location of the cable failure, and then use a reliable intermediate joint for repair. After the repair is completed, do not rush to power on. First, measure the insulation resistance with 5000V insulation resistance to see if it is qualified. If it is not qualified, make a new joint. If it is qualified, use a series resonant voltage withstand device to conduct an AC voltage withstand test on the cable. The test voltage can be applied according to 1.6U0, For a duration of 60 minutes, all joints that pass the inspection should be made into cable wells to avoid direct burial in the soil and not placed in low-lying areas to prevent moisture from causing further failures.
Guidance and suggestions
High voltage cables, whether directly buried, pipeline, or tunnel laying, can be quite troublesome. Time based power also provides the following suggestions to avoid cable damage:
1. When laying cables, safety technicians are equipped on the construction site to be responsible for the safety work of the entire cable laying process.
2. The cable laying project should have a dedicated on-site dispatcher to provide unified command and arrangement for cable laying.
3. For cable laying construction personnel, follow the professional on-site dispatch and command, and do not leave their positions arbitrarily during the operation.