Solid insulated and filled cables are specifically designed for use in coal mines, where they are commonly employed for laying pipes. These cables feature a unique construction in which the core and shielding layer are filled or sealed with petroleum jelly to prevent moisture ingress, ensuring reliable performance in the challenging conditions of underground coal mining environments. Under typical temperature ranges of 30°C to 60°C found in coal mines, the mechanical and electrical properties of coal mining communication cables remain stable. They are widely used for communication lines in roadways, inclines, and electromechanical chambers, as well as for transmitting main signals through shafts, tunnels, and inclined shafts.
A high-quality prefabricated branch cable must meet rigorous performance standards, particularly when it comes to its conductivity, insulation, and mechanical properties. In China, such cables should comply with the GB12706-91 standard, which outlines the essential performance criteria for these types of cables. This standard ensures that the cable is suitable for its intended application, especially in demanding environments like coal mines.
Prefabricated branch cables are manufactured in specialized production lines in factories, based on specific requirements provided by the user. These requirements include the dimensions of the main and branch cables, their length, and the location of the branch points. The entire process is carried out under controlled conditions to ensure consistent quality and reliability.
The performance of the branch connector plays a critical role in determining the overall effectiveness of the prefabricated branch cable. The coupling body connects the main cable to the branch conductor while providing insulation and moisture resistance. Since the internal joints are not visible, it is crucial to perform thorough testing to assess their quality. Two key tests are typically conducted: contact resistance testing and thermal cycling testing.
Contact resistance is measured as the ratio of the contact resistance (R1) to the reference resistance (R2) of the branch cable. For compliance, this ratio should be less than or equal to 1.2. In thermal cycling tests, the main and branch cables are subjected to cycles of heating and cooling. Each cycle involves heating for 5 hours and natural cooling for 3 hours, repeated for a total of 125 cycles. After the 25th cycle, the surface temperature of the coupling should not exceed 75°C. Additionally, the surface temperature after each subsequent cycle should not be more than 8°C higher than that recorded at the 25th cycle.
Resistance is a fundamental property of materials that affects the flow of electric current. Materials with low resistance allow electrons to move freely, resulting in higher current flow, while those with high resistance impede electron movement. Conductors are materials with minimal resistance, allowing efficient current transmission, whereas insulators have very high resistance and prevent current flow.
The YFD series of prefabricated branch cables have been tested by the National Mine Cable Quality Supervision and Inspection Center. Their contact resistance ratio R1/R2 is only 0.7, and the surface temperature of the coupling after the 25th thermal cycle was 43°C, which is well below the 75°C limit. From the 26th to the 125th cycle, the highest recorded temperature was 47°C, still significantly lower than the 51°C threshold.
Thermal cycling refers to the repeated process of heating and cooling that occurs within a system, often seen in industrial applications such as reactors. In such systems, heat transfer circuits are typically separated from the power circuit to avoid contamination and maintain safety, especially in environments where radioactive materials may be involved.
Ultimately, the performance of the branch coupling body depends heavily on the materials used and the manufacturing process. Designers and engineers must pay close attention to the quality of the cable, the selection of joint materials, and the precision of the production tools and techniques. Ensuring these factors are properly managed is essential for delivering safe, reliable, and long-lasting prefabricated branch cables.
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