Research shows that the heat generation of power line insulators consists of three parts.
One is the heat generated by the polarization effect of the dielectric excited under the action of the working frequency voltage.
Second, the internal penetrating leakage current heating.
The third is the surface creepage leakage current heat generation.
When the insulator is in good operating condition, heat generation is mainly the first item. When the porcelain insulator performance deterioration, or porcelain cracking, or porcelain plate surface dirt, will make the second or third leakage current increase, heat increase, resulting in the insulator temperature rise. At present, it is believed that there are three main reasons for insulator deterioration: improper control of the manufacturing process, internal defects, and the influence of changes in the operating environment.
Due to problems in the manufacturing process and formulation, microcracks and hygroscopic porosity are easily formed inside the ceramic and may cause uneven internal stresses. Local stress concentration will increase the microcrack, water through the crack, through holes in the gas phase into the porcelain body, hygroscopic pores for water molecules to provide a space to reside. Water and glass phase stress-induced chemical reaction, thus inducing the slow expansion of the crack. Under the working frequency voltage condition, the water molecules rub against each other in the process of turning polarization, and the heat generated in the area of intense molecular movement will cause a significant local temperature rise of the insulator.
In power systems, rod-shaped porcelain pillar insulators are widely used in busbar and isolation barriers. During the long-term operation, the combined effect of mechanical, thermal, electrical, and environmental factors makes various physical and chemical changes inevitable. As a result, the electrical performance and mechanical strength of the insulator will decrease gradually with the increase of operating hours.