I. Introduction In the 1950s, China's electromechanical manufacturing industry lagged behind, and cable supply was not specialized, lacking the conditions to develop electrical equipment wire and cable products. The mandatory implementation of measures such as "replacing lead with plastic" and "replacing rubber with plastic" in the 1960s strongly promoted technological progress, and this major product category began to take shape. In the 1990s, the market economy gradually matured, and the demand for electrical equipment wires and cables surged, developing into an independent major product category配套 (supporting) engineering projects. Its output value proportion remained at 25-30%. Electrical equipment cables are complementary products, and the sales of various varieties are unstable, depending on the rise and fall of other industries. For example, prefabricated branch cables for high-rise buildings initially had no domestic brands and could only be imported. A few pioneers in branch cables developed the market and innovated technology, gaining a stable market share and extremely high profit returns, achieving domestic production. Under this opportunity, many cable factories hastily started production, causing prices to drop to near-competitive levels. However, this coincided with national restrictions on high-rise building construction, leading to a contraction in market demand, and the high profit returns became a bubble. The demands of users are becoming increasingly complex, and factories can only follow suit. Sometimes, they even have to comply with unreasonable demands, which puts them in a dilemma and can even lead to unfair competition. II. Wires and Cables for Modern Transportation Vehicles 1. Locomotive and Rolling Stock Cables Electric, fuel and steam power, passenger cars, freight cars and special trains have different requirements for cables. Therefore, there are many types of cables in this category, and they are representative. Some of these types can also be used for other vehicles. The current trend is: (1) 3kV and below natural rubber insulated cables should be phased out. (2) 3kV and below chlorosulfonated polyethylene insulated cables need to be retained. (3) 3kV and below ethylene propylene rubber insulated cables are one of the main series. (4) 3kV and below halogen-free low-smoke cross-linked polyolefin insulated cables are the second main series. (5) 30kV ethylene propylene rubber insulated locomotive and rolling stock power cables are a special type. At present, they are basically produced according to TB/T1484, and GB/T12528 is being revised. The most difficult product in locomotive and rolling stock is halogen-free low-smoke cross-linked polyolefin thin-walled insulated cable. Their contents differ, and a comparison table is available in the GB/T standard for reference. 2. Urban Rail Transit DC Power Cables: Urban rail transit is an essential route for the development of transportation in large cities. The planned lengths of urban rail transit in relevant cities are: Beijing 332 km; Tianjin 130 km; Shanghai 240 km; Shenzhen 546 km. Other cities have successively started construction. Light rail uses DC power supply, with rated voltages of 1500V and 750V. Shanghai Shentong Company has formulated enterprise standards: positive cable 1500V; negative cable 300V; conductor cross-section 400mm²; rigid structure cable uses type 2 conductor; flexible structure cable uses type 6 conductor; insulation is either cross-linked polyolefin or ethylene propylene rubber, with a nominal insulation thickness of 2.0mm; a water-blocking layer should be present outside the insulation; other waterproof, fire-resistant, and armored layers are optional structures; the sheath is composed of low-smoke halogen-free polyolefin or similar synthetic materials, with a nominal sheath thickness of 3.8mm. The negative cable structure consists only of conductor and insulation. Cable testing items are basically the same as for general power cables. 3. Long stator winding cables in maglev trains are analogous to the rotor of a linear motor, with the track acting as the stator. Long stator winding cables consist of cables wound into sections and laid within the track's grooves. The cable structure is similar to flexible power cables, but the laying conditions are harsh, with a very small bending radius. The total three-phase cable usage is approximately 15 times the length of a single-direction track. At the 52nd International Cable Symposium, Germany presented a paper on cables used in the Shanghai Maglev. The first batch of cables installed on the Shanghai Maglev line had the same structure described in the paper, but problems arose during trial operation. Germany replaced all the cables, debugged them, and put them into operation. After a considerable period, some problems recurred, resulting in a second wave of issues. Germany did not disclose the direct cause. During negotiations for the Shanghai-Hangzhou Maglev line, Germany proposed a new cable structure, emphasizing that it was patented. In my opinion, this doesn't qualify as a patent, but it is protected by patent law and difficult to circumvent. Overall, it seems that Germany's technology in long stator winding cables for maglev trains is not yet fully mature. The rated voltage of the long stator winding cable is 10/1.75kV (considering 20kV); the rated operating temperature is 90℃; the conductor is an aluminum core of 300mm², the insulation is soft EPDM rubber, both the conductor shield and the insulation shield are semi-conductive EPDM rubber, and the sheath is neoprene rubber; the outer layer of the sheath is a fluorine-containing semi-conductive coating. The coating increases lubrication during cable laying. In the 52nd International Cable Conference paper, there was a metal shield outside the insulation shield, but the detailed performance of the neoprene rubber sheath was not described, only that it had suitable electrical properties, mechanical properties, environmental resistance, and could adhere firmly to the coating. The test track for the German maglev train was relatively short, and no abnormalities were found in the long stator cable during the trial operation. The original cable laying situation in Shanghai may have involved single-point grounding. The new cable, which is the one currently in operation, has eliminated the metal shielding in its structure, changed the sheath to semi-conductive neoprene rubber, retained the semi-conductive coating, and adopted an "Ω"-shaped metal ring around the outside of the cable, fixed at regular intervals with screws for grounding. The cable research institute collaborated with factories to jointly develop magnetic levitation long stator cables, which passed type and research tests, laying the foundation for domestic cable manufacturing. However, market changes are unpredictable, and future demand is difficult to forecast. 4. Low-voltage wires and cables for highway vehicles. Low-voltage wires for highway vehicles (referred to as automotive low-voltage wires) are typically processed into wire harnesses according to automotive wiring templates before being installed in vehicles. The automotive wiring harness market is directly related to automobile production and closely linked to the amount of wiring per vehicle. A low-end sedan uses an average of 800m of low-voltage wire, a mid-range sedan an average of 1500m, and a luxury car up to 2500m. Currently, the insulation of automotive low-voltage wires is still mainly polyvinyl chloride (PVC), but some parts require cross-linked polyolefins, thermoplastic elastomers, ethylene propylene rubber, silicone rubber, and even fluoroplastics. The conductors of automotive low-voltage wires, except for motor wires which may use aluminum conductors, are all copper conductors. The latest design aims to further reduce the conductor cross-section to 0.10 mm² or less. Copper's mechanical strength is insufficient for installation requirements, and copper-clad steel wire is currently being considered. The JB/T8139-1999 standard for low-voltage cables (wires) for highway vehicles has limited varieties and cannot fully meet usage requirements. Each automobile manufacturer has its own wire procurement specifications. Current standards formulated by the China Association of Automobile Manufacturers primarily use PVC thin-insulated low-voltage wires, but in reality, cross-linked polyolefin and silicone rubber insulated low-voltage wires are also widely used. They are already being used in high-end cars, digital transmission cables, and optical fibers. 5. Aviation Wires and Cables: Currently, there are two main series of aviation wires and cables: one is polyimide-fluorine 46 composite film wrapped and sintered insulated cable, mainly used in military helicopters, which has been domestically produced, although the composite film is still imported due to quality considerations. The other is irradiated cross-linked ethylene-tetrafluoroethylene copolymer insulated cable, a type widely used in modern military and civilian large aircraft. It is abbreviated as X-ETFE insulated wire. Large military transport aircraft use 7-8 tons of wire per aircraft. X-ETFE has a specific gravity of 1.73, and its working temperature can be increased to 200℃. The single-layer insulation thickness of its thin-walled insulation structure is 0.15mm. The wire is lightweight, has a relatively large current carrying capacity, stable chemical properties, and excellent electrical, mechanical, and radiation resistance properties. It is also one of the major varieties used in aerospace vehicles. Ten years later, my country will still choose this variety when it independently produces large passenger aircraft. X-ETFE (X-F40) insulated aviation wires and cables are technically difficult to manufacture. Almost every production process has some problems. (1) The single wire bundle stranding requires high precision, and there must be no jumpers in the outer layer, otherwise the minimum insulation thickness will not meet the requirements. (2) At present, there is no domestic supply of insulation raw materials, and they need to be imported from DuPont or Daikin. (3) At present, the domestic solution has not yet solved the problem of suitable sensitizers. Importing sensitizer masterbatch particles is very difficult. Importing finished particles that can be directly extruded and crosslinked by radiation is extremely expensive. (4) Developing raw materials and their mixing and granulation on our own is very difficult in terms of equipment and process. (5) Thin insulation extrusion of wires is difficult to control, such as parameters like eccentricity and stretch ratio. (6) The ideal irradiation dose needs to be studied to obtain the best degree of crosslinking. (7) The post-treatment conditions of irradiated wires need to be studied; otherwise, the electrical and mechanical properties may not fully meet the standard requirements. my country's military standards for aviation wires and cables, and fluoroplastic cables, are equivalent to the US military standards. Polyimide-fluorine 46 composite film wrapped sintered insulated cables are no longer recommended for use by the US Navy, and further observation is needed. 6. Marine cables my country's shipbuilding will approach 10 million tons per year, and Shanghai is building an even larger shipyard, which is said to be the world's largest. The current order situation for marine cables from various marine cable manufacturers is optimistic. Flame-retardant cables for civilian ships fully comply with the latest IEC standards, and halogen-free low-smoke cables can generally meet Class A requirements when bundled for burning. The mainstream insulation materials are crosslinked polyolefins and ethylene propylene rubber, while natural-butadiene rubber has been phased out. Some cable factories can manufacture control and instrument cables according to Dutch standards. General wires and cables for military ships can be supplied domestically. Specialized deep-water longitudinally sealed cables have surpassed conventional levels, with depths exceeding 600m. Defense-grade ultra-high tensile strength sonar cables have also reached a very high level. my country's military ship cable standards are equivalent to US military standards. 7. Development of New Materials Besides marine cables, all vehicle cables used in non-power systems share a common characteristic: they require lightweight, small, thin-walled insulation, abrasion resistance, oil resistance, flame retardancy, and moisture resistance. Some require a temperature rating of 125℃, and a few 150℃. Given the large volume of wires used, using fluoroplastic insulation is uneconomical due to its high price and excessively high performance margin. Currently, the performance of cross-linked polyolefins is not ideal; according to many wire sampling tests, cross-linked polyolefin insulated wires are often on the verge of being unqualified, thus lacking safety and reliability. Furthermore, the manufacturing process requires an additional irradiation cross-linking step. A different approach, such as abandoning cross-linked polyolefins and developing new materials, might be more effective. The development and promotion of new materials should meet the following requirements: a) Operating temperature of 125–150℃. b) Can be thermoplastically extruded without cross-linking. c) Can be extruded for thin-wall insulation. d) Relatively soft and easy to install. e) Main properties exceed those of cross-linked polyolefins. f) Reliable raw material sources. g) Short development period. g) Acceptable price. Polyester (PET), polybutylene terephthalate (PBT), polyethersulfone (PES), and polyether ether ketone (PEEK) are materials that can be developed, but require modification. PEEK has the best performance, but the price is too high. Operating temperatures: PET 120℃, PBT 150℃, PES 150℃, PEEK 200℃. These materials have high elastic modulus, are essentially non-toxic, flame-retardant and self-extinguishing, and can be extruded for thin-wall insulation. III. Nuclear Power Plant 1E Class Cables 1. General Development Situation China has a highly centralized approval authority for nuclear power plant construction. It is estimated that 27 to 32 new 1,000 MW-class nuclear power units will be built by 2020. In other words, starting from 2004, approximately 30 million kilowatts of new nuclear power capacity will be added over 16 years, with two to three nuclear power units starting construction each year. By 2020, the proportion of nuclear power in total power generation capacity will rise from the current 1.8% to 4%. Because nuclear power plants currently require large amounts of water to operate, the main focus of nuclear power plant planning is on the southeastern coastal provinces. Regarding investment in nuclear power construction, foreign economic experts estimate that, conservatively, the investment for such a large-scale nuclear power project would exceed US$40 billion. China National Nuclear Corporation (CNNC) hopes that the average localization rate of newly built nuclear power plants can reach 60%, estimating that US$24 billion (approximately RMB 200 billion) worth of goods could be domestically produced. Analyzing my country's wire and cable industry, with further improvements in equipment and product development based on current cable manufacturing technology, the localization rate of wires and cables could reach over 95%. Currently, my country's nuclear power plants under construction are mainly pressurized water reactor systems. 2. The verification of the 40-year service life of K3 class cables has a somewhat abstract meaning; the Arrhenius equation is a commonly used method. Life assessment testing of new materials is a research endeavor, not a standard performance indicator. Forty years is a long time; even with accelerated aging tests over a relatively short period, the estimated lifespan won't be exactly 40 years, but could be between 20 and 60 years. This doesn't easily determine whether a new material meets usage requirements. Factors in the accelerated aging test design, such as temperature range, temperature gradients, specimen shape, surface area in contact with air, specimen thickness, specimen fabrication process, material uniformity of batch specimens, specimen lifespan termination parameters, and oven ventilation, all affect the estimated results. Designing a perfect scheme requires multiple rounds of preliminary verification to obtain satisfactory conclusions. my country has produced 1E-grade K3 category cables for many years, and all certified products have undergone 40-year lifespan assessments. Due to various interests, some believe it's effective; some believe it's basically credible; some believe it's basically unreliable; and some even believe it should be completely overturned and the industry should be reshuffled. Ultimately, user acceptance is the most important factor. It's worth considering the American perspective; this explanation can be confirmed by referring to the conclusions of the EBASCO standard regarding physical life testing. The conclusion is as follows: "During the cable's design life, the conditions encountered during cable operation cannot be completely equivalent to those described by accelerated testing methods in the laboratory, necessitating the application of Arrhenius techniques or other laboratory techniques. Accelerated thermal life testing can only provide relative thermal life data for the material. Furthermore, the results extrapolated from butyl rubber insulated cables indicate that the lifespan derived from accelerated life testing data using Arrhenius techniques, through extrapolation, is lower than the actual lifespan. While such data is insufficient as a permissible generalization, it seems to suggest that the comparison between the accelerated thermal life of a new type of insulation and its proven superior long-term service record provides strong evidence for its long-term usability." Inspired by this conclusion, the longest-lasting radiation-crosslinked insulation for normal-quality low-voltage cables, including non-flame-retardant crosslinked polyethylene insulation, has exceeded 50 years since its invention, while chemical and silane crosslinking have exceeded 40 years. Considering its long-term 90°C thermal life, there is no international doubt that it can achieve a 40-year operational lifespan. However, the highest quality high-filler halogen-free flame-retardant cross-linked polyethylene insulation used for low-voltage cables has not exceeded 30 years since its invention. It has not failed due to thermal aging in actual use. Of course, the reasons for proving that it has reached a 40-year service life are not sufficient. However, the application of relative temperature index comparison test can still explain its essential problem. 3. Cracking of halogen-free low-smoke flame-retardant thermoplastic polyolefin sheath The triangular concept of halogen-free low-smoke cable material is still valid. Electrical, mechanical and flame-retardant properties are three-legged. If one angle is too large, the other two angles will be smaller. Cracking of halogen-free low-smoke sheath is a relatively serious defect. Imported cables also crack. For this reason, material and cable manufacturers have tried their best, but they are not all sure. The problem of sheath cracking does not only occur in nuclear power plants. Other products also have this kind of accident. The following are some issues to pay attention to, which can help reduce the probability of sheath cracking: (1) Choose thermoplastic sheath material with higher elongation at break, such as 200%, but the cost increases and the oxygen index also decreases. (2) Use a larger extruder and control a smaller extrusion volume. (3) Use a low compression ratio screw, a small mesh filter, and select a suitable sheath material. (4) Strengthen the control of the temperature of each section of the screw, the die head and the die opening. (5) Use a cross-linked halogen-free low-smoke sheath, which increases the cost and requires equipment modification. (6) Are there other ways? What if EVM rubber with a VA content of 40-80% is used? 4. Attempts to test the crack resistance of halogen-free low-smoke sheathed cables The current standard crack resistance test method cannot effectively test the crack resistance of the sheath, and there is still no standard test method. Creating prestress on the sample is the main factor that can promote cracking. (1) Take 4 or 8 sections of finished cable as samples, bend the samples in four directions, tie the two ends of the sample together and fix them, and take the inner diameter of the circle as 4 to 8 times the outer diameter of the cable. Make the cable have tensile prestress in four directions. (2) The samples are subjected to hot and cold cycling treatment. The high temperature point is not higher than the cable's working temperature, and the low temperature point is not lower than -10℃. The high temperature lasts for 2 hours, followed by 2 hours at room temperature, then 2 hours at low temperature, and finally 2 hours at room temperature. This constitutes one hot and cold cycle. The number of cycles is up to you, and the number of cycles may vary for different materials. (3) The sheath of all samples should be free of cracks. (4) Alternatively, the sheath can be peeled off, and 4 or 8 strip-shaped test pieces can be cut from four parts around the circumference. Take a copper rod with a diameter of 3 to 6 times the thickness of the test piece, wrap the strip-shaped test piece around the copper rod, and fix it. Perform the above hot and cold cycling test. The number of cycles is up to you, and the test piece should be free of cracks. It is indeed difficult to completely solve the cracking problem of halogen-free low-smoke sheaths. If we change our approach and take the low-smoke low-halogen rubber-type technical route, the problem can be solved. Recently, the United States introduced cables for nuclear power plants, but did not emphasize halogen-free and low-smoke. Instead, it suggested the use of low-smoke chlorosulfonated polyethylene sheaths. If my country imports nuclear power plant technology from the United States, it may change the only recognized halogen-free and low-smoke technical route. 5. Regarding K1 category cables: K1 category cables are used far less frequently than K3 category cables, while their development costs are several times higher. Therefore, there are relatively fewer manufacturers developing K1 category cables. Currently, a few cable manufacturers have produced some K1 category cable varieties that have passed technical appraisal. Based on experience, K1 category cables using EPDM rubber insulation and EPDM rubber sheathing are relatively more likely to pass leakage accident tests. Cross-linked polyolefin insulation and cross-linked polyolefin sheathing are relatively less likely to pass leakage accident tests. This is not to exclude the use of cross-linked polyolefin. Currently, leakage accident tests in China are conducted in principle with reference to IEEE 383-1974. This standard itself states that test conditions can be varied. In previous years, domestic test equipment was not perfect, and test methods were not standardized. It is said that test conditions in Beijing are now better, and they are combined with nuclear industry design institutes. Currently, Shanghai cannot conduct complete leakage accident tests. The specific procedures for leakage accident tests are not entirely the same abroad or domestically. Even within the same country, the procedures are not entirely the same now as in the past. In general, due to insufficient test experience, further discussion is needed to determine which procedure is the most orthodox and authoritative. There are still very few domestic companies that have passed the K1 category cable certification, but the full localization of domestic production is not far off.