The impact of temperature rise on the insulation resistance of mining lightweight cables is essentially achieved by changing the microstructure and charge movement state of the insulation material, which directly leads to a significant decrease in resistance value. This impact has regularity and destructiveness, and should be given special attention in high-temperature environments of mines.
The insulation performance of insulation materials (such as chloroprene rubber and polyvinyl chloride commonly used in mining cables) depends on the "binding force" of their molecular structure on free electrons. When the temperature rises, this binding force will be weakened:
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The thermal motion of molecules intensifies with increasing temperature, and the vibration amplitude of atoms and electrons inside the insulation layer increases. Electrons that were originally firmly bound are more likely to gain energy and break free from molecular gravity to form directional movement (i.e. enhanced conductivity);
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From the data, for every 10 ℃ increase in temperature, the insulation resistance usually decreases by 30% -50%. For example, a certain type of mining lightweight cable has an insulation resistance of 1000M Ω at 25 ℃, and when the ambient temperature rises to 45 ℃, the resistance may drop sharply to below 250M Ω.
The sensitivity of different materials to temperature varies, which directly affects the decrease in resistance:
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Rubber insulation (such as natural rubber, chloroprene rubber)Weak high temperature resistance. When the temperature exceeds 60 ℃, the molecular chain is prone to oxidation and breakage, producing more conductive impurities inside. The resistance value decreases 2-3 times faster than that of plastics. For example, at 65 ℃, the insulation resistance of rubber may decrease by more than 70% compared to room temperature;
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Plastic insulation (such as polyvinyl chloride, polyethylene)The molecular structure is more stable, but when the temperature exceeds 80 ℃, plasticizers will accelerate their volatilization, causing the material to become brittle. At the same time, the increase in pores leads to intensified charge leakage, and the resistance value will also decrease significantly.
If the cable in the mine is close to the equipment heat dissipation area or high-temperature coal seam, the local temperature may exceed 70 ℃. At this time, regardless of the material, the insulation resistance will fall below the conventional qualified standard (such as 0.5M Ω).
Short term high temperature leads to a temporary decrease in resistance, while long-term high temperature can cause irreversible insulation aging:
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Continuous high temperature can cause the insulation layer to harden, crack, and become sticky, forming long-lasting conductive channels inside the material. Even if the temperature returns to normal, the resistance cannot return to its initial level;
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For example, if a cable runs continuously in a 50 ℃ environment for 6 months, its insulation resistance may decrease from the initial 500M Ω to below 50M Ω, and it cannot be restored through drying treatment in the future, so the cable can only be replaced.
This is also why mining cables are clearly marked with the "maximum allowable working temperature" (such as 60 ℃, 70 ℃). Once the temperature is exceeded for a long time, the attenuation of insulation resistance will enter the "acceleration channel".
The increase in temperature has a dual effect of "enhancing charge mobility" and "damaging material structure", resulting in a significant decrease in insulation resistance of mining lightweight cables. Moreover, the longer the duration and amplitude of high temperature, the more irreversible the impact. In practical applications, it is necessary to control the ambient temperature by keeping away from heat sources, strengthening ventilation and cooling, and other measures. At the same time, when detecting insulation resistance, the cable must be cooled to the ambient temperature first to avoid misjudgment of "false non conformities" caused by high temperature. It is also important to be alert to the risk of insulation aging under long-term high temperature.
This article is generated by AI