Common types of railway power cable faults include ground faults, short-circuit faults, flashover faults, open-circuit faults, and comprehensive faults.
Abstract: With the rapid development of science and technology, the railway power system is becoming more and more complete, and the electrified mileage is extending accordingly. The power system in railways 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 provides power to the沿线 facilities after processing through the railway substation. 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 seriously affect 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 the 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 self-closed circuit of the railway power system, the task of the self-closed circuit is mainly to supply power to railway stations and electrical equipment such as signaling based on the normally operating 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 ground faults, short-circuit faults, flashover faults, open-circuit faults, and comprehensive faults. (1) Short-circuit fault refers to the contact between single-phase or multi-phase transmission lines forming a destructive large current. 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 the equipment or make it unable to operate normally. (2) Ground fault refers to the transmission line being connected to the earth without passing through an insulator, which is a type of short-circuit fault and has great harm.
(3) Flashover fault refers to the sudden breakdown of the cable during the high-voltage holding period, 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) Open-circuit fault, also known as circuit break fault, refers 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 fault refers to the simultaneous occurrence of two or more of the above faults, which has great tail number and very complex fault conditions [1].
Cables will be damaged by mechanical effects, making them unable to work normally and causing great harm. Mechanically damaged cables are generally caused by construction personnel not surveying the construction site during construction, causing engineering machinery used in construction to damage the cable to a certain extent, or not properly setting up cable protection measures, making it easy for the cable 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 high current conditions, which can easily cause cable 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 may penetrate into the cable trench, corroding the cable insulation layer and directly destroying the cable insulation performance. 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 damage factors will be considered in cable design, continuously optimizing the cable design and processing procedures 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 cable use.
Reasonable and scientific selection of cable laying path is the key to ensuring cable operation quality, and scientific design of drainage methods should be carried out in combination with specific requirements.
Without qualified cable laying quality and standardized laying operations, it is easy to cause problems such as damage to the cable protective layer and mechanical damage to the cable. 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 under the cover of the cable insulation layer, causing the damaged conductor to continuously reduce the insulation strength of the cable insulation layer at that point during operation due to temperature increase, thereby causing cable faults. In response to this situation, during cable installation, the turning angle of the power cable should be effectively controlled, and the cable should be bent as naturally as possible to avoid mechanical damage caused by excessive turning. During cable laying, the outer sheath of the cable should be thoroughly inspected, and both ends of the cable should be checked for moisture. In addition, the continuity of the cable conductor and the insulation between phases and between phase and ground should be strictly tested. Cables should be laid neatly, and reinforcement should be carried out if necessary. 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 parts is low and prone to faults. Therefore, sufficient cable should be reserved at these two parts to prevent cable accidents. The insulation materials used at these two places should also meet technical indicators. If these two parts do not have good sealing conditions, it will also lead to cable faults. 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 positions and equipment during cable laying. 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. For cables, attention should be paid to inspection during laying; regular cable operation tests should be conducted to monitor the changes in cable operation quality, ensuring timely repair or replacement and ensuring 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 cable transmission situation and external structural status, find out the problems existing in cable facilities, and test various indicators. For example, when overhead cables need to exceed buildings, the vertical distance 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 grounding devices related to operating cable lines, and carry out grounding resistance value testing to determine whether it matches the design requirements. Problems should be discovered and handled in a timely manner. Seal the cable to isolate it from the atmosphere as much as possible to avoid moisture problems. In addition, trees at both ends and below the line should be trimmed to ensure appropriate width of the line, timely clean debris on the surface of insulators, and clean debris and bird nests around poles.
At present, China's railway construction is developing rapidly. In order to ensure the safety and stability of railway system development, it is necessary to ensure the safe and reliable operation of the power system and pay attention to the operation quality of power cables. The faults that are prone to occur in power cables should be analyzed in order to take reasonable measures to prevent and handle them. In addition, railway power cables should be regularly inspected, and more experience should be accumulated in handling 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.
