The insulation resistance of mining lightweight cables is like an "environmentally sensitive body". Factors such as humidity, temperature, and pollutants in the environment can directly "attack" the insulation layer through physical and chemical reactions, causing fluctuations or even sudden drops in resistance values. The core reason is that the resistance performance of the insulation layer depends on the integrity of its material structure, and the special nature of the mining environment can easily disrupt this balance.
Water is a conductive substance. When the humidity in a mine exceeds 80%, a layer of water film will be adsorbed on the surface of the insulation layer, and even moisture will seep into the insulation material through the small gaps in the sheath (especially for aged cables).
The surface water film will form a "surface leakage current", which is equivalent to connecting a conductive channel in parallel to the insulation layer, resulting in a low resistance value during measurement;
If moisture enters the interior of the insulation layer (such as when the joint seal is poor), it will directly reduce the volume resistivity of the material. For example, when the polyvinyl chloride insulation layer is fully dry, the resistance can reach 10 ¹⁴Ω· cm, but after being dampened, it may drop to below 10 ⁸Ω· cm, a decrease of more than a million times.
That's why the cable surface must be wiped dry before testing, and the qualification standards in humid environments need to be stricter.
The effect of temperature on insulation resistance shows a "reverse relationship": as the temperature increases, the resistance value will significantly decrease.
From the perspective of material principles, the molecular thermal motion of insulation layers (such as chlorinated polyethylene and natural rubber) intensifies with increasing temperature, making it easier for internal free electrons to move directionally and enhancing conductivity;
If the cable in the mine is close to a heat source (such as equipment heat dissipation port, high-temperature rock wall), the local temperature may exceed 60 ℃, and the insulation resistance may decrease by more than 50% compared to normal temperature.
Therefore, the standard requires that the cable be cooled to ambient temperature during testing, otherwise it may be misjudged as insulation aging.
Pollutants such as gas, dust, and acidic/alkaline water in mines can affect insulation resistance in two ways:
chemical corrosionHydrogen sulfide in gas and salt in dust (such as chloride commonly found in mine water) can react with insulation materials, such as rubber sheaths being oxidized and cracked, and polyvinyl chloride becoming hard due to loss of plasticizers, resulting in damage to the insulation layer structure and a decrease in resistance value;
Conductive bridgingConductive dust (such as coal dust mixed with moisture) will adhere to the surface of the cable, forming a continuous conductive path, especially at the joints. The accumulation of pollutants may directly cause the insulation resistance to be lower than the safe value (0.5M Ω).
Seemingly physical damage, it actually amplifies the impact of the environment:
When the sheath is worn by rocks and cracks appear, moisture and pollutants will directly invade the interior of the insulation layer. Even if the environmental humidity is normal, local moisture will cause a sudden drop in resistance;
The fatigue damage of the insulation layer caused by frequent bending will form small air gaps, which will be filled with water vapor in high humidity environments, becoming a "breeding ground" for partial discharge and further eroding the insulation performance.
The insulation resistance of mining lightweight cables is essentially the ability of materials to isolate current, and the high humidity, high temperature, and multi pollutant environment of mines precisely destroys this ability from three dimensions: the introduction of conductive media (moisture, pollutants), the weakening of material properties (temperature, corrosion), and the failure of structural protection (mechanical damage+environmental invasion). Therefore, when detecting insulation resistance, it is necessary to analyze the values in conjunction with environmental conditions, and the core of daily protection is to block the "direct contact" between environmental factors and the insulation layer.
This article is generated by AI