Abstract: With the rapid development of science and technology, the railway power system is becoming more and more perfect, and the electrified mileage extends accordingly. The power system in the railway has the function of traction power supply and can provide power to facilities along the railway line. Its power source is the power supply department along the railway line. The railway connects to the local power supply, and after being processed by the railway substation, it provides power along the line. Only by ensuring the safe and reliable quality of railway power cables can this process be carried out smoothly. If there are faults, it will directly damage the power supply equipment and have a serious impact on the operation of railway trains. This requires relevant personnel to master the faults that are prone to occur in railway power cables, understand the causes of faults, and formulate preventive measures based on this to ensure the quality of power cables and provide guarantee for the safe operation of trains.
Whether the railway system can operate safely and stably will be affected by the operation of its power system. The power system is responsible for supplying electricity to grassroots units such as stations, locomotive depots, vehicle depots, and signal depots along the railway line. Especially in the aspect of the self-closed line of the railway power system, the task of the self-closed line is mainly to supply power to railway stations and electrical equipment such as signal equipment based on the normal operation of the railway system, ensuring the continuity, safety, and reliability of power supply, laying a solid foundation for the normal operation of the railway system, and enabling trains to run safely. Power cables are an important part of the power system, so it is necessary to ensure the quality of power cables. However, in actual operation, power cables are prone to faults, which have a serious impact on the entire power system and even the railway system. Relevant personnel need to take reasonable measures to prevent power cable faults and ensure the quality and efficiency of cable application.
Common types of railway power cable faults include grounding faults, short-circuit faults, flashover faults, disconnection faults, and comprehensive faults. (1) Short-circuit faults refer to the contact between single-phase or multi-phase transmission lines forming destructive large currents. If a short-circuit fault occurs in a power cable, the large current will rapidly increase the conductor temperature, damaging the insulation properties of the cable, which will damage equipment or make it unable to operate normally. (2) Grounding faults refer to the transmission line being connected to the earth without insulation, which is a type of short-circuit fault and has great harm.
(3) Flashover faults refer to the cable being suddenly broken down during high-voltage holding, and the fault can continue to maintain the voltage under this voltage. After the cable layer is broken down by high voltage, it will affect the surrounding equipment to a certain extent, and even threaten the personal safety of workers. (4) Disconnection faults, also known as open-circuit faults, refer to the transmission line being disconnected, unable to transmit electrical energy normally, and the electrical equipment will be directly powered off, or even damaged, affecting the development of important work. (5) Comprehensive faults refer to the simultaneous occurrence of two or more of the above faults, which have great tail number and very complex fault conditions [1].
Cables can be damaged by mechanical effects, causing the cable to fail to work normally and causing great harm. Mechanically damaged cables are generally caused by construction personnel not surveying the construction site during construction, so that the engineering machinery used in construction damages the cable to a certain extent, or the cable protection measures are not reasonably set, making it easy to suffer mechanical damage. In addition, overloading and stretching of cables during construction will also cause mechanical damage faults. Excessive bending, stretching, and folding can easily cause faults in cable joints and intermediate connection wires. This type of cable fault is relatively common.
If the insulation layer of the cable ages, it will reduce the insulation capacity of the cable and cause serious damage to the cable. Cables generally operate under high voltage and large current conditions, and are prone to heating. Overheating of the cable will affect the insulation performance of the cable to a certain extent, thereby seriously affecting the physical and chemical properties of the cable. In addition, cables buried deep underground are in a humid environment for a long time, and some fertilizers and chemical substances will penetrate into the cable trench, corroding the insulation layer of the cable and directly destroying the insulation performance of the cable. In addition, after the insulation performance of the cable decreases, it will affect the corrosion resistance and heat dissipation performance of the cable, which will also accelerate the aging of the cable insulation layer, forming a vicious cycle [2].
During the use of cables, problems such as insulation aging and mechanical damage are prone to occur. Therefore, these potential destructive factors will be considered in cable design, and the design and processing procedures of cables will be continuously optimized to extend the service life of cables. However, different cable manufacturers may have some manufacturers who cut corners, or do not produce according to the design drawings, or use materials that do not meet quality standards to reduce costs, resulting in cable quality not meeting relevant standards, leaving safety hazards for the use of cables.
Reasonable and scientific selection of cable laying path is the key to ensuring the quality of cable operation, and the drainage method should be scientifically designed according to specific requirements.
Without qualified cable laying quality and standardized laying operations, problems such as damage to the cable protective layer and mechanical damage to the cable are prone to occur. When laying railway power cables, if the power cable has a large turning angle, it is easy to damage the inside of the conductor. This is a mechanical damage problem, but it is difficult to find this problem under the cover of the cable insulation layer, resulting in the damaged conductor reducing the insulation strength of the cable insulation layer at that place due to temperature increase during operation, and then causing cable faults. In response to this situation, during the cable installation process, the turning angle of the power cable should be effectively controlled, and the cable should be bent naturally as much as possible to avoid mechanical damage caused by excessive turning. During the cable laying process, the outer sheath of the cable should be fully inspected, and both ends of the cable should be checked for moisture. In addition, the continuity of the cable conductor, the insulation between phases, and the insulation between phase and ground should be strictly tested. The cables laid should be arranged neatly, and if necessary, reinforcement should be carried out. The distance between cables laid in parallel should comply with the specification requirements.
In the entire cable, the insulation strength at the terminal head and intermediate joint is relatively low and prone to faults. Therefore, sufficient cables should be reserved at these two locations to prevent cable accidents. The insulation materials used at these two locations should also meet technical indicators. If these two locations do not have good sealing conditions, cable faults will also occur. After moisture intrusion, the insulation level of the cable will be reduced, so attention should be paid to the moisture-proof conditions of these special locations and equipment when laying cables. When stripping the cable, care should be taken, especially when stripping the semiconductor layer, to avoid damaging the main insulation.
After the construction of the power cable project, preventive tests for handover and operation supervision should be carried out according to regulations. Check for injuries during the cable laying process; conduct regular cable operation tests to monitor changes in the quality of the cable during operation, ensure timely repair or replacement, and ensure the normal development of power supply work.
In order to reduce the fault rate, it is necessary to formulate a scientific, reliable, and reasonable daily maintenance system based on the actual operation of the distribution network, and implement this system in actual work. When carrying out maintenance work, professional personnel should be arranged to regularly inspect the power transmission situation and external structural status of the cable, find out the problems existing in the cable facilities, and test various indicators. For example, when the overhead cable needs to exceed the building, the vertical distance requirement should not be less than 2.5m, and the horizontal distance from permanent buildings should not be less than 0.75m. Check the integrity of the grounding device related to the cable line in operation, and carry out grounding resistance value testing, judge whether it is consistent with the design requirements, and find and deal with problems in a timely manner. Seal the cable to isolate it from the atmosphere as much as possible to avoid moisture problems in the cable. In addition, the trees at both ends and below the line should be trimmed to ensure that the line has an appropriate width, clean up debris on the surface of the insulator in a timely manner, and clean up debris and bird nests around the pole.
At present, China's railway construction is developing rapidly. In order to ensure the safety and stability of the railway system, it is necessary to ensure the safe and reliable operation of the power system, and attention should be paid to the operation quality of power cables. The faults that are prone to occur in power cables should be analyzed so that reasonable measures can be taken to prevent and handle them. In addition, railway power cables should be inspected regularly, and more experience should be accumulated when dealing with faults to promote the further development of railway construction.
[1] Guo Yu. Exploration on the management mode of railway power cable operation and maintenance [J]. China Equipment Engineering, 2020(05):71-73.
