The brittle fracture of the mandrel during the operation of the composite insulator is generally considered to be caused by the poor sealing of the connection part of the mandrel and the hardware, resulting in the cracking of the weak interface of the adhesive bonding between the sealant and the hardware, and the external acid rain directly penetrates into the exposed part of the mandrel through the split gap, slowly corroding the cross section of the mandrel. However, from the investigation and analysis of more than 30 brittle composite insulators by relevant foreign departments, there are only 4 to 5 cases of breakage in the exposed part of the connection between the product and the hardware, and the rest occur above the connection part of the core rod and the hardware, located in the part where the first umbrella dress is protected by the sheath. The anatomical inspection of several cases of brittle fracture of composite insulators in China also found that the fracture of mandrel did not occur in the exposed part of the stress concentration of the mandrel, but was located near the end of the metal tool with sheath seal. It can be seen that the mandrel of composite insulator is rarely broken due to the direct action of external acid rain.
The composite insulator is a long rod insulation structure with very small capacitance between stages, and the voltage distribution of the insulation part is very uneven. Although there is a voltage equalizing ring at the end of the product wire, its voltage gradient is still quite large, and the end hardware will not appear corona during normal operation, but the field strength is almost the same as the corona field strength. At the end of the product wire, there is the highest field strength. This high field strength accelerates the diffusion of saturated water medium in the exposed part of the mandrel along the glass fiber through the epoxy resin with good permeability to the part with low concentration. In this way, the acid anhydride vulcanizer that is impossible to evenly remain in the epoxy resin accelerates the penetration of water molecules, so that there is water medium in the circumference of the mandrel with high field strength.
In addition, the corona of the external hardware end under abnormal natural conditions or various overvoltage conditions makes N2 in the air on the surface of the sheath generate NO2, so that NO2, which is more than 20 times higher than N2 permeability, will spread from the surface of the sheath to the interior with lower concentration, and react with the internal water medium to generate nitric acid. Due to the constant flow of water medium and the frequent penetration and diffusion of NO2, the cross section of the mandrel is slowly corroded and causes fracture. In the composite insulators with brittle fracture at home and abroad, most of the core rod fractures occur in the parts with the highest electric field intensity, which can also prove the credibility of the above analysis.
In addition, even if the product end seal quality is good, if there is a local insulation defect or surface loss on the product wire jacket, it will often store saturated water medium and permeate the mandrel surface through the water vapor through the well-performing jacket. At the same time, the NO2 gas generated in the corona often diffuses from the surface of the sheath or the defect or damage to the surface of the mandrel, reacts with the existing water medium to form nitric acid, and corrodes the mandrel at high potential, resulting in fracture.
The above is the brittle break of the composite insulator, I hope it will be of great help to you! If you want to buy quality composite insulator can contact us!
