Electrothermal Coupling: Critical Evolution Before Insulator Flashover

Transmission lines in operation face complex stress environments. When the system experiences an overvoltage disturbance, if composite suspension insulator is already in a state of temperature rise, its electrical performance will change significantly. This phenomenon involves the intersection of materials science and high-voltage technology.

Thermal effects alter dielectric properties

polymer suspension insulator withstands heat generated by leakage current and dielectric loss during long-term operation. In severely polluted or aging sections, the local temperature rise can be several times the normal value. The increase in material temperature leads to a decrease in volume resistivity and a decrease in dielectric strength. Studies have shown that as the aging process deepens, the energy level of the suspension type insulator surface traps continuously increases, enhancing its charge trapping ability.

After corona aging, silicone rubber materials develop flocculent material, cracks, and pores on their surface. These microstructural changes make the material surface more susceptible to moisture absorption, significantly reducing wet flashover voltage. Heating defects in composite insulators are often related to poor core-sheath bonding; this defect is the direct cause of core rot and overheating.

Chain reaction after overvoltage superposition

Overvoltage superposition on the already heated composite tension insulator causes electric field distortion. Under temperature gradient conditions, the surface electric field redistributes. The electric field strength at the high-voltage end and the contact area with the metal inserts can rise to several times the normal value, becoming the initiation point of partial discharge. Infrared detection shows that some AC composite insulators exhibit severe heating characteristics within one year of operation, and the heating area is not limited to the high-voltage end.

In the electrothermal coupling field, the trapping characteristics and charge transport behavior of the material change. The temperature rise increases the carrier mobility and exacerbates the erosion of the material surface by partial discharge. This process has a self-accelerating characteristic. Analysis of the samples returned to the site confirmed that, with the increase in service life, the surface of the high voltage transmission line insulators was severely pulverized, organic polymer chains were broken, a large number of small molecules were generated, and the flashover voltage continued to decline.

Surface discharge is first triggered at weak points where the dielectric strength decreases. The heat generated by the discharge channel further expands the damaged area. After experiencing a voltage surge, the residual conductive channels inside the overhead power line insulators will significantly reduce the subsequent flashover voltage threshold.