What are the factors that affect the insulation resistance of wires and cables?
Wires and cables often encounter the phenomenon of low insulation resistance in production. There are many factors that affect the insulation resistance value of cables. In fact, there are mainly four factors that have a great influence on the insulation resistance coefficient.
1. The influence of temperature
As the temperature increases, the insulation resistance coefficient decreases. This is due to the increase in thermal motion, the increase in the generation and migration of ions. Under the action of voltage, the conduction current formed by the movement of ions increases, and the insulation resistance decreases. Theory and practice show that the insulation resistance coefficient decreases exponentially with the increase of temperature, and the conductivity increases exponentially with the increase of temperature.
2. The influence of electric field strength
When the electric field strength is in a relatively low range, the mobility of ions increases in a proportional relationship with the increase of electric field strength. Ionic current and electric field strength follow Ohm's law. When the electric field strength is relatively high, as the electric field strength increases, the mobility of ions gradually changes from a linear relationship to an exponential relationship. When the electric field strength is close to breakdown, a large amount of electron migration will occur, thereby greatly reducing the insulation resistance coefficient. The withstand voltage test voltage of various wire and cable products specified in the standard is in the stage where the ion mobility increases proportionally with the electric field strength, so the influence of the electric field strength on the insulation resistance coefficient cannot be reflected. When the sample is subjected to breakdown test, the influence of electric field on insulation resistance coefficient is clearly reflected.
3. The influence of humidity
Due to the high conductivity of water, the size of water molecules is much smaller than that of polymer molecules. Under the action of heat, the polymer macromolecules and the constituent chain segments move relatively, so that water molecules can easily penetrate into the polymer, increase the conductive ions in the polymer, and reduce the insulation resistance. This standard specifies the immersion test of various wires and cables. For example, before measuring the insulation resistance, the rubber test piece is immersed in water for 24 hours. The purpose is to meet the influence of moisture and water on electrical properties during use.
Insulation resistance is one of the main electrical properties of insulating materials and an important indicator of wire and cable products or materials. Generally, the insulation resistance is required to be no less than a certain value. If the insulation resistance value is too low, the leakage current along the wire and cable line will inevitably increase, resulting in a waste of electrical energy. At the same time, the electrical energy will be converted into thermal energy, preparing for thermal breakdown and increasing the possibility of thermal breakdown.
4. The influence of material purity
Impurities are mixed into the material, increasing the conductive particles in the material and reducing the insulation resistance. Therefore, the insulation resistance of a certain rubber and plastic material will reflect the purity of the material and verify whether it meets the standard. In the production process of wires and cables, if the process does not strictly follow the operating procedures, mixed impurities and materials will bubble due to moisture, insulation core deviation or outer diameter size is smaller than the standard, insulation delamination or cracks, insulation scratches, etc., the insulation resistance of the product will be reduced.
Therefore, in order to check the insulation resistance, it is necessary to check whether there are any problems in the process operation. During the use of wires and cables, measuring the changes in insulation resistance can also check the insulation damage and prevent accidents.
