As an important part of urban public transport, the metro system has extremely high requirements for the safety, stability and continuity of its power supply system. Metro power systems mainly include high-voltage distribution, traction power supply, low-voltage distribution, lighting, ventilation, signal communication and other links, in which power cables are laid intensively, with complex environments, narrow installation space, high safety standards and long-term uninterrupted operation requirements. Cold shrink cable accessories, with their excellent electrical properties, convenient construction, strong environmental adaptability and long service life, have become the preferred supporting products for cable connection and termination in metro power engineering. This paper systematically expounds the application characteristics, application scenarios, selection requirements, installation points and operation and maintenance precautions of cold shrink cable accessories in metro power systems.

The metro power supply system generally adopts 10kV and 35kV voltage levels, and a large number of XLPE insulated power cables are used. The operation environment of metro cables is quite special: most cables are laid in underground tunnels, cable trenches, pipe galleries and mechanical and electrical equipment rooms, with characteristics such as high humidity, possible water accumulation, poor ventilation, limited space, and vibration caused by train operation for a long time. In addition, metro stations and tunnel sections cross complex geological and hydrological conditions, and some sections face risks such as moisture, salt fog, and chemical corrosion. Traditional heat-shrink cable accessories require open-flame heating during installation, which is not only inefficient but also prone to potential fire hazards in underground confined spaces; while prefabricated cable accessories have high requirements for construction accuracy and high cost, which is difficult to adapt to large-scale metro engineering. Cold shrink cable accessories are made of high-performance silicone rubber or EPDM materials with high elasticity, which are pre-expanded on plastic support tubes during production. During installation, only the support strips need to be drawn out, and the accessories can automatically shrink and tightly wrap the cable body by relying on their own elastic recovery force, without open fire, without special tools, and with high construction efficiency, which is very suitable for the narrow and closed environment of the metro.

In the metro traction power supply system, cold shrink cable terminals and intermediate joints are widely used in the connection between traction substations, rectifier units, DC switchgears and traction network cables. Traction power supply undertakes the power supply task of metro trains, and its reliability directly affects the normal operation of trains. The cables here have large cross-section, high load rate, and frequent current changes. Cold shrink cable accessories have good electrical stability, low partial discharge, strong resistance to partial discharge and electrical corrosion, which can effectively avoid insulation aging and breakdown caused by electric field concentration. At the same time, the interface between high-quality cold shrink accessories and cables can maintain lasting radial pressure, which can resist the micro-deformation of cables caused by train vibration and prevent interface discharge and water intrusion.

In the metro 10kV/35kV high-voltage distribution system, cold shrink cable accessories are mainly used in the connection of high-voltage inlet and outlet lines of main substations, station distribution rooms, ring network cabinets and switching stations. These lines undertake the power supply of the whole line and each station, with long cable lines and many intermediate joints. The intermediate joint of cold shrink cable adopts integrated injection-molded stress cone and multi-layer sealing structure, which has excellent waterproof and moisture-proof performance. For the tunnel sections where water seepage may occur, the fully sealed cold shrink intermediate joint can meet the requirements of long-term reliable operation under water immersion conditions, greatly reducing the fault rate of cable lines. In addition, the high-voltage cable terminals in the station equipment room mostly use indoor cold shrink terminals, which have a compact structure, do not occupy too much space, and have good insulation performance, adapting to the intensive layout of metro electrical equipment.

The metro auxiliary power supply system includes lighting, air conditioning, escalators, water pumps, ventilation fans, fire fighting, monitoring and other equipment, mostly using low-voltage power cables. Although the voltage level is low, the number of cables is large, the laying is complicated, and the construction period is tight. Cold shrink cable accessories are fast and convenient to install, which can significantly shorten the on-site construction time and help the metro project to be completed and put into operation on schedule. At the same time, cold shrink materials have good flame retardant and low smoke halogen-free properties, which can meet the strict fire protection standards of metro systems. In case of fire, they can reduce the release of toxic smoke and prevent the spread of fire, ensuring the safety of personnel and equipment.

In terms of application in special metro sections, cold shrink cable accessories also show strong adaptability. In the elevated metro sections, the cables are affected by outdoor wind, rain, sunlight and temperature changes, and outdoor cold shrink terminals with umbrella skirts are usually used, which have good hydrophobicity, anti-ultraviolet and anti-pollution flashover performance. In the underground deep buried sections and cross-river tunnel sections, the cable environment is humid and high in external pressure, and the cold shrink intermediate joint with reinforced sealing and mechanical protection can ensure long-term stable operation. For sections with high electromagnetic interference, the good shielding performance of cold shrink cable accessories can reduce the interference to metro signal and communication systems, ensuring the accuracy of train operation control.

In the metro engineering application, the selection of cold shrink cable accessories must strictly match the cable voltage level, cross-sectional area, core number and insulation structure. 10kV cables should be matched with 10kV cold shrink terminals and intermediate joints, and 35kV cables should use 35kV full-series cold shrink products to ensure electrical performance safety. The material of accessories should be high-quality silicone rubber with excellent elasticity, aging resistance, low temperature resistance and high temperature resistance, so as to adapt to the temperature and humidity changes in the metro environment. Products must have complete type test reports, in line with national standards and IEC standards, and meet the access requirements of metro engineering suppliers. At the same time, flame retardant, low smoke and halogen-free properties are essential indicators to ensure the fire safety of the metro.

During installation, the construction personnel need to carry out standard operation according to the metro power engineering specifications. Before installation, the cable surface should be cleaned and polished to remove oil, dust and burrs to ensure good fit between the accessories and the cable. The stripping size of the cable insulation layer, semi-conductive layer and shielding layer must be accurate to avoid damage to the cable body. When extracting the support strip of cold shrink accessories, uniform speed should be maintained to ensure uniform shrinkage and avoid wrinkles or gaps. After installation, insulation resistance test, AC withstand voltage test and partial discharge test should be carried out to confirm that the installation quality is qualified before putting into operation.

In the operation and maintenance of the metro power system, the later maintenance workload of cold shrink cable accessories is small, but regular inspection is still required. Operation and maintenance personnel should regularly check whether the terminals and joints have overheating, discharge, aging, damage and water seepage through infrared temperature measurement, visual inspection and instrument detection. For the joints in the tunnel with high humidity, the sealing condition should be focused on checking to prevent insulation performance degradation caused by moisture. In the daily maintenance, it is forbidden to knock or squeeze the cable accessories at will to avoid mechanical damage. With good installation quality and proper maintenance, cold shrink cable accessories can achieve a service life of more than 30 years in the metro power system, matching the life cycle of metro lines.

In conclusion, cold shrink cable accessories play an irreplaceable role in the metro power system due to their superior electrical performance, convenient construction, strong environmental adaptability and high operational reliability. They are widely used in traction power supply, high-voltage distribution, auxiliary power supply and other links, effectively ensuring the safety, stability and continuity of metro power supply. With the rapid development of urban metro construction in various countries, the demand for high-quality cold shrink cable accessories will further increase. In engineering practice, strict selection, standardized installation and scientific maintenance are the important guarantees to give full play to the performance advantages of cold shrink cable accessories and support the efficient and safe operation of the metro power system.