What Factors Affect The Insulation Resistance of Wires And Cables?

We know that the insulation layer of wires and cables will affect their resistance, so what are the factors that affect the insulation resistance of wires and cables?     

There are many factors that affect the insulation resistance of cable. In fact, there are four main factors that have a great influence on the insulation resistance coefficient.

1.Effect of temperature

With the increase of temperature, the insulation resistance coefficient decreases. This is due to the increase of thermal movement and the increase of ion generation and migration. Under the action of voltage, the conduction current formed by ion movement 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.Effect of electric field strength      

When the electric field strength is in a relatively low range, the mobility of ions increases proportionally with the increase of electric field strength. The ion current and electric field intensity follow Ohm's law. When the electric field strength is relatively high, with the increase of electric field strength, the mobility of ions gradually changes from linear relationship to exponential relationship. When the electric field strength is close to breakdown, there will be a lot of electron migration, so the insulation resistance coefficient will be greatly reduced.  

The voltage of withstand voltage test of various wire and cable products specified in the standard is in the phase of increasing ion mobility and electric field strength in proportion, so the influence of electric field strength on insulation resistance coefficient cannot be reflected. The influence of electric field on the insulation resistance coefficient is obviously reflected when the sample is subjected to breakdown test.

3.Effect of humidity      

Due to the large conductivity of water, the size of water molecules is much smaller than that of polymer molecules. Under the action of heat, polymer macro-molecules and constituent chains move relatively, making water molecules easily penetrate into polymer, increasing conductive ions in polymer and reducing insulation resistance. This standard specifies immersion tests for 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 impact of water and water on electrical performance during use.        

Insulation resistance is one of the main electrical properties of insulating materials, and also an important index of wire and cable products or materials. Generally, the insulation resistance shall not be lower than a certain value. If the insulation resistance is too low, the leakage current along the wires and cables will inevitably increase, resulting in the waste of electric energy. At the same time, electric energy will become heat energy, which is ready for thermal breakdown and increases the possibility of thermal breakdown.

4.Influence of material purity          

Impurities mixed into the material increase the conductive particles in the material and reduce 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, the process is not strictly in accordance with the operating procedures, mixed impurities and materials are blistered due to moisture, the deviation of the insulation core or the outer diameter is smaller than the standard, the insulation is stratified or cracked, the insulation is scratched, etc. Will reduce the insulation resistance of the product.            

Therefore, in order to check the insulation resistance, it is necessary to check whether there are any problems in the process operation. In the process of using wires and cables, measuring the change of insulation resistance can also check the insulation damage to prevent accidents.