Solid insulated filled cables are ideal for installation in coal mine environments and are primarily used for piping applications. The core of the cable, along with its shielding layer, is filled or poured with petroleum jelly to prevent moisture from entering the coal mine, which can cause damage or failure. Under typical temperature conditions in coal mines—ranging from 30°C to 60°C—the mechanical and electrical properties of coal mining communication cables remain stable. These cables are commonly used for communication lines in roadways, inclined shafts, and electromechanical chambers, as well as for transmitting main signals in tunnels, vertical shafts, or inclined shafts.
A high-quality prefabricated branch cable must meet strict performance standards, especially in mining environments. Domestic products should comply with the GB12706-91 standard, ensuring that the conductor, insulation, and mechanical properties of the materials meet the required specifications. These are essential criteria for prefabricated branch cable products.
Prefabricated branch cables are manufactured in factories using specialized production equipment, tailored to the specific requirements of the user. This includes the dimensions of the main and branch cables, their length, and the position of the branches. These cables are produced on dedicated production lines, ensuring consistency and quality.
The performance of the branch connectors is crucial, as it directly affects the reliability of the entire prefabricated branch cable system. The branch coupling body connects the main cable to the branch cable’s conductor while providing insulation and moisture resistance. From an external perspective, it's impossible to assess the internal joint quality without testing. Two key tests are used to evaluate joint performance: contact resistance testing and thermal cycling tests.
The ratio of contact resistance (R1) to the reference resistance (R2) of the branch cable should be ≤ 1.2. For the thermal cycling test, the main and branch cables are subjected to a cycle of heating for 5 hours and natural cooling for 3 hours. This process is repeated for a total of 125 cycles. After the 25th cycle, the surface temperature of the coupling should not exceed 75°C. Additionally, after each cycle, the surface temperature of the joint should not exceed the 25th cycle temperature by more than 8°C.
Resistance is a property of materials that opposes the flow of electric current. The higher the resistance, the lower the electron flux, and vice versa. Materials with low or no resistance are called conductors, while those that block current flow are known as insulators.
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 0.7, and the surface temperature at the 25th thermal cycle is 43°C, which is below the 75°C limit. From the 26th to the 125th cycle, the maximum temperature reached is 47°C, also under the 51°C threshold.
Thermal cycling refers to a process where heat is transferred between different parts of a system. In a reactor, the heat transfer circuit is typically isolated from the power circuit to prevent radioactive contamination of the power system.
Ultimately, the performance of the branch coupling body depends heavily on the material used and the manufacturing process. Designers and engineers must pay close attention to the quality of the prefabricated branch cable, the choice of joint materials, and the production techniques involved to ensure long-term reliability and safety.
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