In recent years, the country has paid more and more attention to the safety of power grid operation. Power cables are an important part of power engineering. They are used for power transmission and distribution. Power and other advantages, but in use there are also problems such as overheating of cable joints, mechanical damage to the protective layer, aging and deterioration of insulation, causing overvoltage and harmonic faults, cable faults, terminal head and intermediate joint design, cable technology and material selection, etc., once it occurs Cable accidents will not only cause certain property losses to the country, but also endanger the lives of the people. Based on this, it is necessary to start with the common faults of the power grid to analyze the causes of the faults and the corresponding countermeasures.

1. Power cable fault analysis

(1) Power cable overload breakdown. Cables are often in continuous operation during long-term use. Such overload operation will cause defects such as cable insulation aging and semiconductor expansion cracks. If they are not discovered in time, the defects will gradually expand. When the power load is large, it is easy As a result, the temperature of the cable core rises, and under the long-term high temperature, the insulation aging is increasingly aggravated, the service life is shortened, and cable faults are gradually developed.

(2) The material of the cable head or the intermediate joint. The quality of the materials used for cable joints also has a certain impact on cable faults. In order to pursue profits, many enterprises choose some heat-shrinkable materials with lower intervals for construction. During operation, the cable itself will generate heat. Because the cable insulation material and the material of the cable head are different, thermal expansion and contraction will also occur in different degrees. Cracks will occur between the cable and the cable head material after long-term operation, resulting in current leakage. The cable joint is released to the semiconductor through leakage, causing the cable insulation to be broken down and causing cable failure.

(3) The power cable breaks down due to resonance overvoltage. When some circuits are applied to the voltage of the same amplitude for many times, it will cause a certain degree of insulation damage each time, resulting in insulation reduction during normal operation, resulting in weak insulation, and when the harmonic overvoltage exceeds the limit value of the cable damage part, it will cause cable damage. breakdown.

(4) Manufacturing process of cable terminals. Corona discharge at the cable terminal is mainly due to the small distance between the three cores of the cable, and the gap between the cores forms a capacitor, which can cause phase-to-phase or ground discharge, and long-term discharge will damage the cable terminal.

Second, the cause analysis of power cable faults

(1) Mechanical damage. A large proportion of cable failures are due to mechanical damage caused by humans during the original installation, or due to damage caused by nearby cable repairs after installation. Moreover, if the damage is serious, people will repair it in time, but the subtle damage cannot be discovered or treated in time, so that the damaged part will gradually expand after a long time, and the insulator will gradually lose its protective effect, causing the damaged part to completely collapse and form a fault.

(2) Insulation aging and deterioration. Due to its own characteristics, the cable insulation will be affected after the power is heated for a long time, and its own insulation capacity will be reduced. Surveys show that 19% of cable faults are due to changes in insulation. Under the action of the electric field, the insulating medium of the cable is dissociated, which reduces the insulation capacity; when the medium is in an ionized state, ozone will be generated in the air gap, and the insulating medium will be corroded. If the temperature is too high, the insulation will age and deteriorate, and the free air gap in the cable will cause local overheating, which will cause carbonization of the insulation. In a cable overload condition, the cable runs beyond its maximum load capacity. In areas where cables are densely populated, if the ventilation of cable channels and cable trenches is not good, the cables and nearby heat pipes will be damaged due to excessive temperature.

(3) Corrosion of the cable sheath. There are two types of cable sheath corrosion: chemical corrosion and electrical corrosion. Under normal circumstances, electrical corrosion mainly occurs when there is strong electric power around the cable, most of which are in the underground electric field around the cable, and the cable will undergo electrical corrosion due to its influence. In places where cables are installed, if there are gas stations and acid-base operations, the cables will be chemically corroded, resulting in cable failures.

(4) Overvoltage. There are two types of overvoltage within the cable and atmospheric overvoltage. Relevant studies have shown that the occurrence of cable faults in the external environment is mainly caused by atmospheric overvoltage. In addition, problems with the cable itself can cause the cable to fail when it is exposed to overvoltage.

(5) Loss of cable insulation. During the construction of the cable, there will be a difference in the height of the cable due to different terrains. With downward flow of insulating oil, the insulation of the cable is reduced, causing the cable to fail. This type of failure mainly occurs in non-drip cables and oil-impregnated paper cables.

(6) Poor design and manufacturing process. Cable is a high-risk manufacturing industry that needs to be protected. It requires rigorous design, material selection, and construction to reflect its safety. Improper handling of any link will have adverse effects on society. However, some companies pursue economic benefits while ignoring its safety in the manufacturing process. Specifically, it is mainly reflected in the following aspects: sheath defects during cable manufacturing, crack damage and other defects during packaging insulation; cable accessories manufacturing Defects, such as sand holes in cast iron, insufficient mechanical strength of ceramics, unqualified quality of attached materials, and negligent maintenance and management of insulation materials by later staff, resulting in damp cable insulation materials and so on.

3. Countermeasures against cable faults

(1) Load monitoring. There are obvious differences in power load consumption in different regions and in different periods. During the peak period of relatively large power consumption, the cable is in an overloaded state. At this time, if the cable is kept overloaded for a long time, it will cause a large The damage of the cable shortens the service life of the cable. In order to prevent cable problems caused by overload, manual monitoring should be implemented during the operation of the cable, and the load in the cable should be controlled manually to prevent the cable from being overloaded for a long time. In the current research on load monitoring, it is recommended to install high-performance monitoring instruments in the cables to monitor the operating load of the cables and protect the operation of the cables based on the load.

(2) Monitor the temperature. The influence of temperature on the cable is also relatively large. High temperature will destroy the running state of the cable, which is not conducive to ensuring the stability of the cable. There is a close relationship between temperature and load, and load can also cause dangerous problems of high temperature cables. When the demand for cables continues to rise, a large amount of heat will accumulate on the cables, destroying the overall structure of the cables. Aiming at the problem of abnormal temperature in the cable, it is necessary to adopt a monitoring method to monitor the temperature state of the cable in an all-round way during operation, to find out the situation of excessive temperature in time and to implement reasonable treatment methods. Cables are installed in a wide range, and there will be some difficulties in monitoring the temperature. The operating temperature of the cables should be well controlled to prevent cable failures due to temperature out of control.

(3) Prevent corrosion. The running distance of cables in the power system is long, and some cables involve operations such as overhead and buried, which makes the cables face the risk of corrosion during operation. Cables buried underground are most susceptible to corrosion when exposed to moisture. Underground cables will be corroded to varying degrees according to the underground environment, so it is necessary to implement cable corrosion protection. When installing cables, anti-corrosion work should be done in advance, keep a dry installation environment, choose soil with anti-corrosion effects, and the cables buried underground should not come into contact with chemical and biological corrosion substances. Protects the jacket from corrosion problems. Overhead cables should also be equipped with a protective layer. Whether they are buried underground or overhead cables, inspections must be done regularly, and corrosion problems should be dealt with immediately to avoid large-scale corrosion.

(4) Operation management. The operation and management of cable lines can prevent cable failures and prevent cable failure problems. During the operation and management of cables, excavate the middle head well at least once a year, check the quality and performance of the cable lines in the well, and focus on checking whether there is water, corrosion, sundries, etc. in the cables; In order to avoid the risk of failure in the line operation, the inspection and maintenance work shall be arranged in an all-round way. Operation management personnel use ultrasonic partial discharge test equipment, infrared imaging equipment, etc. to check the terminal head of the cable, and check whether the terminal head has problems of partial discharge and temperature heating. In the operation management, the cables that have been in operation for more than 15 years are taken as the key detection objects. Before the cables reach the peak load, the operation management should be arranged to ensure that the cables have safe operation conditions. The shock wave partial discharge test should be arranged for the cables according to the operation management plan. The feeder automatic switch is installed in the cable. When the cable fails, the feeder automatic switch can quickly isolate the fault. During the cable fault prevention period, use the method of operation management to manage all the equipment in the cable, such as relay protectors, to ensure the reliability of various equipment in the cable and reduce the probability of cable faults.