Insulation Requirements for Track Components
Why is the insulation performance of track accessories crucial for electrified railways?
The track circuit of electrified railways relies on current to transmit signals. Insulated accessories can block current leakage between rails and sleepers or the ground, ensuring accurate signal transmission. If the insulation performance fails, stray current will corrode metal components such as bolts and rail spikes, shortening their service life and increasing maintenance costs. Poor insulation may also lead to signal misjudgment, affecting train dispatching safety and causing operational accidents. The national standard requires that insulated accessories maintain stable insulation performance in the environment of -40℃ to 80℃ to meet long-term use needs. Key accessories such as fasteners, fishplates, and under-sleeper pads of electrified railways must have insulation functions to form a complete insulation system.
What are the core components and insulation principle of insulated fasteners?
Insulated fasteners are mainly composed of insulated base plates, insulated gauge blocks, nylon sleeves and other components, each of which is made of insulating materials or covered with an insulating layer. The insulated base plate is set between the rail and the sleeper to block longitudinal current conduction; the insulated gauge block isolates the rail from the spring clip to prevent lateral current leakage. The nylon sleeve wraps the bolt to avoid direct contact between the bolt and the sleeper concrete, forming electrical isolation. The insulating material is usually glass fiber reinforced polyamide 66, which has excellent insulation performance and sufficient strength and wear resistance. Insulated fasteners construct an all-round insulation barrier through the synergy of various components to ensure the normal operation of the track circuit.
How to test whether the insulation performance of track accessories meets the standards?
Common testing methods include insulation resistance testing, which requires the insulation resistance value of accessories to be not lower than the specified standard to ensure no current leakage channels. Conduct a voltage withstand test, apply a certain AC or DC voltage, observe whether breakdown occurs, and verify the insulation strength. In actual lines, the insulation performance can be indirectly judged through track circuit signal detection; if the signal transmission is abnormal, there may be insulation failure. Regularly conduct visual inspections on the accessories in use to check for damage or aging of the insulation layer, and promptly replace damaged components. Some important lines will adopt online monitoring systems to real-time monitor changes in insulation performance and prevent potential risks.
What are the impacts of stray current on track accessories in urban rail transit and protective measures?
Urban rail transit trains start and stop frequently, generating a large amount of stray current. These currents will leak through track accessories, corroding metal components and concrete structures. Stray current corrosion will cause bolt fracture and fishplate cracking, seriously affecting track structure safety and increasing maintenance frequency and costs. Protective measures include selecting high-performance insulated accessories to block the stray current conduction path; installing current drainage devices in the track circuit to guide stray current to flow back safely. Regularly detect the distribution of stray current, promptly identify high corrosion risk areas and take strengthening measures; adopt anti-corrosion coatings for metal accessories to achieve double protection against corrosion. Optimize the design of the train traction system to reduce the generation of stray current and control corrosion risks from the source.
How to select the material of insulated accessories under different environmental conditions?
In normal temperature and dry environments, ordinary glass fiber reinforced polyamide 66 insulated accessories can be selected, which have high cost performance and can meet basic insulation requirements. In high-temperature and high-humidity environments (such as southern coastal areas), moisture and heat aging resistant insulating materials must be selected to avoid insulation layer failure due to moisture. In alpine regions, low-temperature resistant insulating materials must be selected to prevent material embrittlement and insulation performance degradation caused by low temperatures. In corrosive environments (such as saline-alkali land, near chemical plants), chemical corrosion resistant insulating materials must be selected, combined with metal components with anti-corrosion coatings. The tunnel environment is closed, so flame-retardant insulating materials must be selected to improve fire safety performance and avoid toxic gas generation in case of fire.