A high-voltage cable is a kind of power cable and refers to a main road used to transmit power cables between 10KV-35KV (1KV=1000V) and is mostly used for power transmission. The product implementation standards for high-voltage cables are GB/T12706.2-2008 and GB/T12706.3-2008.
The cable is the bridge between the power supply equipment and the electrical equipment, and plays the role of transmitting electrical energy. Because of its wide application, faults often occur. The following briefly analyzes the causes of the common problems of high-voltage cables. The classification based on the causes of faults can be roughly divided into the following categories: manufacturer's manufacturing reasons, construction quality reasons, design unit design reasons, and external force destruction Four categories.
First, the manufacturer of manufacturing reasons The manufacturer of manufacturing reasons according to the different parts of the site, is divided into cable body reason, cable connector reason, cable grounding system causes three categories.
1. Causes of manufacturing of cable body Generally, the problems that are likely to occur in the cable production process include eccentricity of insulation, uneven thickness of insulation shield, impurities in insulation, protrusions inside and outside shielding, uneven degree of cross-linking, moisture in cable, and sheathing of cable metal sheath. Poor, etc., Some situations may be more serious. Failures may occur during or shortly after completion of the test, and most of them are in the form of defects in the cable system, causing serious hidden troubles in the long-term safe operation of the cable.
2. Reasons for the manufacture of cable joints High-voltage cable joints have previously used wrap-around type, die-cast type, and molded type, and require a large amount of work to be produced on site. Because of the limitations of on-site conditions and the manufacturing process, insulation layers are not allowed. Avoid air gaps and impurities, so problems can easily occur. The types commonly used in China are assembly and prefabrication.
The cable joints are divided into cable end connectors and cable intermediate joints. No matter what the joint type is, the cable joint failure usually occurs at the fracture of the cable insulation shield because it is the site where the electrical stress is concentrated and the cause of the cable joint failure due to manufacturing reasons is stress. Cone body manufacturing defects, insulation filler problems, oil leaking seals and other reasons.
3, cable grounding system, including cable grounding box, cable grounding protection box (with protective layer protector), cable cross-interconnected box, sheath protection and other parts. The general problem that is easy to occur is mainly because the poor sealing of the box body leads to multi-point grounding, causing the metal sheath induction current to be too large. In addition, the selection of protective layer protector parameters is unreasonable or the quality of the zinc oxide crystal is unstable, and the protective layer protector is easily damaged.
II. Causes of Construction Quality There are many cases of high-voltage cable system failures due to construction quality. The main reasons are as follows: First, the site conditions are relatively poor, cables and joints are manufactured at the factory with high environmental and process requirements, and the construction site Temperature, humidity and dust are not well controlled. Secondly, during the cable construction, it is inevitable that tiny scratches will be left on the insulating surface. The semi-conductive particles and the sand on the abrasive cloth may also be embedded in the insulation. In addition, during the construction of the joint, the insulation is exposed to the air and the insulation is also inhaled. Moisture, these all leave hidden dangers for long-term safe operation. Third, the installation did not strictly follow the process of construction or process regulations did not take into account the possible problems. The fourth is that the DC voltage withstand test results in the formation of a back-EMF in the joint resulting in insulation failure. The fifth is due to poor sealing. The middle joint must adopt the sealed structure of metal copper shell plus PE or PVC insulation coating to ensure the solidity of the seal during construction on site, which effectively ensures the sealing and waterproof performance of the joint.
Third, the design due to the thermal expansion of the cable caused by cable crushing lead to breakdown. When the cross-linking cable load is high, the temperature of the core is increased, the cable is heated to expand, and the cable is turned on the bracket elevation at the turning point in the tunnel. The long-term heavy-duty operation of the cable has a large amount of peristaltic force, causing the bracket facade to crush the outer jacket of the cable. , Metal sheathing, intrusion into the cable insulation leads to cable breakdown.
The cable is the bridge between the power supply equipment and the electrical equipment, and plays the role of transmitting electrical energy. Because of its wide application, faults often occur. The following briefly analyzes the causes of the common problems of high-voltage cables. The classification based on the causes of faults can be roughly divided into the following categories: manufacturer's manufacturing reasons, construction quality reasons, design unit design reasons, and external force destruction Four categories.
First, the manufacturer of manufacturing reasons The manufacturer of manufacturing reasons according to the different parts of the site, is divided into cable body reason, cable connector reason, cable grounding system causes three categories.
1. Causes of manufacturing of cable body Generally, the problems that are likely to occur in the cable production process include eccentricity of insulation, uneven thickness of insulation shield, impurities in insulation, protrusions inside and outside shielding, uneven degree of cross-linking, moisture in cable, and sheathing of cable metal sheath. Poor, etc., Some situations may be more serious. Failures may occur during or shortly after completion of the test, and most of them are in the form of defects in the cable system, causing serious hidden troubles in the long-term safe operation of the cable.
2. Reasons for the manufacture of cable joints High-voltage cable joints have previously used wrap-around type, die-cast type, and molded type, and require a large amount of work to be produced on site. Because of the limitations of on-site conditions and the manufacturing process, insulation layers are not allowed. Avoid air gaps and impurities, so problems can easily occur. The types commonly used in China are assembly and prefabrication.
The cable joints are divided into cable end connectors and cable intermediate joints. No matter what the joint type is, the cable joint failure usually occurs at the fracture of the cable insulation shield because it is the site where the electrical stress is concentrated and the cause of the cable joint failure due to manufacturing reasons is stress. Cone body manufacturing defects, insulation filler problems, oil leaking seals and other reasons.
3, cable grounding system, including cable grounding box, cable grounding protection box (with protective layer protector), cable cross-interconnected box, sheath protection and other parts. The general problem that is easy to occur is mainly because the poor sealing of the box body leads to multi-point grounding, causing the metal sheath induction current to be too large. In addition, the selection of protective layer protector parameters is unreasonable or the quality of the zinc oxide crystal is unstable, and the protective layer protector is easily damaged.
II. Causes of Construction Quality There are many cases of high-voltage cable system failures due to construction quality. The main reasons are as follows: First, the site conditions are relatively poor, cables and joints are manufactured at the factory with high environmental and process requirements, and the construction site Temperature, humidity and dust are not well controlled. Secondly, during the cable construction, it is inevitable that tiny scratches will be left on the insulating surface. The semi-conductive particles and the sand on the abrasive cloth may also be embedded in the insulation. In addition, during the construction of the joint, the insulation is exposed to the air and the insulation is also inhaled. Moisture, these all leave hidden dangers for long-term safe operation. Third, the installation did not strictly follow the process of construction or process regulations did not take into account the possible problems. The fourth is that the DC voltage withstand test results in the formation of a back-EMF in the joint resulting in insulation failure. The fifth is due to poor sealing. The middle joint must adopt the sealed structure of metal copper shell plus PE or PVC insulation coating to ensure the solidity of the seal during construction on site, which effectively ensures the sealing and waterproof performance of the joint.
Third, the design due to the thermal expansion of the cable caused by cable crushing lead to breakdown. When the cross-linking cable load is high, the temperature of the core is increased, the cable is heated to expand, and the cable is turned on the bracket elevation at the turning point in the tunnel. The long-term heavy-duty operation of the cable has a large amount of peristaltic force, causing the bracket facade to crush the outer jacket of the cable. , Metal sheathing, intrusion into the cable insulation leads to cable breakdown.
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