The insulation resistance of wire and cable products is mainly measured by measuring the volume resistance of cable insulation, and surface resistance is not measured. There are many factors that affect the insulation resistance value of cables, and in practice, there are four main factors that have a significant impact on the insulation resistance coefficient.
Temperature influence
As the temperature rises, the insulation resistance coefficient decreases. This is due to the increase in thermal motion, which leads to an increase in the generation and migration of ions. Under the action of voltage, the conduction current formed by ion motion increases, resulting in a decrease in insulation resistance. Theory and practice have shown that the insulation resistance coefficient decreases exponentially with increasing temperature, while the conductivity increases exponentially with increasing temperature.
The influence of electric field strength
When the electric field strength is within a relatively low range, the migration rate of ions increases with the increase of electric field strength. The ion current and electric field strength follow Ohm's law. When the electric field strength is relatively high, the trend of ion migration increasing with the increase of electric field strength gradually changes from a linear relationship to an exponential relationship. When approaching breakdown, a large amount of electron migration will also occur, and the insulation resistance coefficient will be greatly reduced.
The withstand voltage test voltage for various wire and cable products specified in the standard is in the stage where the ion migration rate increases proportionally with the electric field strength, so the influence of electric field strength on the insulation resistance coefficient cannot be reflected. When conducting a breakdown test on the test piece sample, the influence of electric field on the insulation resistance coefficient is clearly reflected.
The impact of humidity
Due to the high conductivity of small molecules and the much smaller size of water molecules compared to polymer molecules, under thermal action, polymer macromolecules and their constituent chains move relative to each other, making it easier for water molecules to penetrate into the polymer, increasing the number of conductive ions inside the polymer and reducing the insulation resistance.
The standard specifies immersion tests for various wires and cables, such as immersing rubber test pieces in water for 24 hours before measuring insulation resistance, in order to avoid the impact of moisture and water on electrical performance during use.
Insulation resistance is one of the main electrical properties of insulation materials and an important indicator of wire and cable products or materials. Generally, insulation resistance is required to not be lower than a certain value. If the insulation resistance value is too low, the leakage current along the wire and cable line will inevitably increase, causing waste of electrical energy. At the same time, electrical energy becomes thermal energy, preparing conditions for thermal breakdown and increasing the possibility of thermal breakdown.
In DC cable insulation, materials with different resistance coefficients can also be used to form graded insulation to improve material utilization. Improving surface resistance coefficient is also very important for cable insulation. When there is dirt and moisture on the surface, due to its uneven distribution, it may cause some surfaces to withstand high voltage, leading to partial discharge or surface discharge, causing serious faults. However, sometimes manual methods are also needed to reduce surface resistance, For example, the conductive core of a cable may have uneven electric field distribution due to incomplete smoothness of the surface, and high electric field strength can cause corona discharge. Coating the surface of the conductive core with conductive rubber or semi conductive plastic will reduce the surface electric field strength and eliminate corona. Additionally, the degree of moisture absorption of the material can be determined based on the change in the resistance coefficient of the insulation material.
The influence of material purity
Impurities mixed in the material increase the conductive particles in the material, causing a decrease in 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 requirements. In the process of wire and cable production, if the operating procedures are not strictly followed during the manufacturing process, mixed impurities, materials that are damp and blister, insulation deviation or outer diameter size smaller than the standard specifications, insulation layering or cracks, insulation scratches, etc., can all reduce the insulation resistance of the product. Therefore, when checking the insulation resistance, it is necessary to check whether there are any problems during the process operation. During the use of wires and cables, measuring the change in insulation resistance can also check for insulation damage and prevent accidents.
To improve the safety of home circuits, the editor suggests using low smoke, halogen-free, flame-retardant cables as home wiring. Cable companies have always used high-purity oxygen free copper as the core to prevent overload, while using independently developed environmentally friendly materials as insulation, greatly reducing the risk of leakage and short circuit. Using it as a ground wire provides multiple protections for your family, so cables that meet national standards can ensure our life safety. Never hold onto the mentality of luck. Once an accident occurs, regret is beyond our reach!
