The main reason for product quality is that the glass parts of glass insulators contain impurity particles, the most common is NIS particles. The phase transformation state of NIS is incomplete in the process of glass melting and annealing. After the insulator is put into operation, it is considered that the slow phase transformation and expansion will cause cracks in the glass.
When the diameter of particle impurities is less than a certain value, it may not be eliminated by thermal and cold shock, resulting in high self-explosion rate of insulators in operation. When the impurity particles are located in the internal tension stress layer of the glass, the probability of self-explosion is higher. Because the glass itself is a brittle material, it can withstand pressure but not tension, so most of the breakage of the glass is caused by tension stress.