What factors can affect mineral-insulated fire-resistant cables?
Release date:
2022-07-26 10:25
Source:
At Mineral-insulated fire-resistant cable During the production process, numerous factors can affect the insulation resistance of mineral-insulated fire-resistant cables, thereby reducing their overall insulation performance. Among these, four factors have a significant impact on the cables.
I. The Influence of Electric Field Strength
According to Ohm's law, when the electric field strength is within a relatively low range, ion mobility increases proportionally with the increase in electric field strength. However, when the electric field strength becomes relatively high, the trend of ion mobility increasing with the electric field gradually shifts from a linear relationship to an exponential one. Near the breakdown point, a significant number of electrons begin to migrate, causing the insulation resistance coefficient to drop dramatically.
II. The Influence of Temperature
Insulation resistance decreases exponentially as temperature rises—specifically, it drops with increasing temperature. This phenomenon is attributed to the enhanced thermal motion, as well as the increased generation and migration of ions. Under the influence of voltage, the conductive current generated by ion movement intensifies, leading to a reduction in insulation resistance.
3. The Influence of Material Purity
The presence of impurities mixed into the material increases the conductive particles within, thereby reducing the insulation resistance. Therefore, the insulation resistance of an insulating material directly reflects its purity and serves as a key indicator to verify whether it meets the specified standards.
IV. The Influence of Humidity
Due to water's high electrical conductivity and the fact that water molecules are much smaller than polymer molecules, thermal energy causes the polymer macromolecules and their chain segments to move relative to one another. This allows water molecules to easily penetrate the polymer, increasing the concentration of conductive ions within the polymer and thereby reducing its insulation resistance.
Insulation resistance is one of the primary electrical properties of insulating materials and serves as an important indicator for wire and cable products or materials. Generally, the insulation resistance is required to be no lower than a specific value. If the insulation resistance falls below this threshold, leakage current along the wires and cables will inevitably increase, leading to wasted electrical energy. At the same time, this electrical energy is converted into heat, creating conditions conducive to thermal breakdown and significantly raising the likelihood of such failure.
During the production of mineral-insulated fire-resistant cables, process controls are often inadequate, leading to impurities being mixed in, materials becoming damp and blistered, insulation core wires deviating from specifications or having diameters smaller than standard, as well as issues such as layered insulation, cracks, or even insulation scratches. These defects can all reduce the product's insulation resistance.
Therefore, when checking insulation resistance, it is necessary to examine whether there are any issues during the manufacturing process. During the use of mineral-insulated fire-resistant cables, measuring changes in insulation resistance can also help detect insulation damage, thereby preventing potential accidents.
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