Discuss the causes of common high voltage cable problems

Cable is a bridge between power supply equipment and electrical equipment, which plays a role in the transmission of electric energy. It is widely used, so faults often occur. The following brief analysis of the causes of common problems of YJV high voltage cable is conducted. According to the causes of faults, they are roughly divided into the following categories: manufacturer's manufacturing reasons, construction quality reasons, design reasons and external damage.

Cable is a bridge between power supply equipment and electrical equipment, which plays a role in the transmission of electric energy. It is widely used, so faults often occur. The following brief analysis of the causes of common problems of YJV high voltage cable is conducted. According to the causes of faults, they are roughly divided into the following categories: manufacturer's manufacturing reasons, construction quality reasons, design reasons and external damage.

First, manufacturer manufacturing reasons

Manufacturers manufacturing reasons according to the different parts, and divided into cable body cause, cable joint cause, cable grounding system three reasons.

1, cable body manufacturing reasons

General problems in manufacturing process of cable insulation eccentricity, insulation shielding thickness is not uniform, insulation, impurities, inner and outer shield has swelled, uneven crosslinking degree of be affected with damp be affected with damp, cable, cable metal sheath seal bad, etc., in some cases more serious may in completed trials or shortly after the operation of malfunction, mostly in the form of defects exist in the cable system, Serious hidden danger to cable long-term safety operation.

2, cable joint manufacturing reasons

High voltage cable joints used to be wrapped, molded, molded and other types, requiring a lot of work to make on site, and because of the limitations of site conditions and production process, there will inevitably be air gaps and impurities between the insulation layers, so it is easy to occur problems. The type commonly used in China is assembly and prefabrication.

Cable joint is divided into cable terminal connector and cable intermediate joint, no matter what form of joint, cable joint fault is generally appear in the cable insulation shielding fracture place, because here is the part of the electrical stress concentration, because of manufacturing reasons resulting in failure of cable joint stress cone body manufacturing defects, the reasons of insulation filler, seal oil, etc.

3. Cable grounding system

Cable grounding system includes cable grounding box, cable grounding protection box (with protective layer protector), cable cross-interconnection box, protective layer protector and other parts. The general problem is mainly because the box seal is not good enough to water, resulting in multi-point grounding, causing the metal protective layer induced current is too large. In addition, improper selection of protective parameters or poor quality zinc oxide crystal instability is also easy to cause protective protective device damage.

Two, construction quality reasons

There are many failures of high voltage cable system due to construction quality, mainly due to the following aspects:

1, the site conditions are relatively poor, the cable and joint in the factory manufacturing environment and process requirements are very high, and the construction site temperature, humidity, dust are not easy to control.

2, cable construction process in the insulation surface will inevitably leave small skid marks, semi-conductive particles and sand on the emery cloth may also be embedded in the insulation, in addition to the joint construction process due to insulation exposure to the air, insulation will also inhale water, all these leave hidden dangers for long-term safe operation.

3, installation is not strictly in accordance with the process of construction or process provisions did not consider the possible problems.

4. Dc withstand voltage test is adopted for completion acceptance, which causes the formation of anti-electric field in the joint and leads to insulation damage.

5, due to poor sealing treatment. The intermediate joint must be sealed with a metal copper shell and PE or PVC insulation anticorrosion layer to ensure the tightness of the lead seal in the field construction, so as to effectively ensure the sealing and waterproof performance of the joint.

Three, design reasons

Cable squeeze caused by thermal expansion leads to breakdown. When the XLV cable is under high load, the core temperature rises and the cable expands under heat. The cable is on the support facade at the bend in the tunnel, and the peristaltic force of the cable is large during long-term heavy load operation, which results in the cable outer sheath and metal sheath crushed by the support facade and the cable insulation layer squeezed into the cable, resulting in cable breakdown.