How Does Electrolyte Ionization Accelerate The Degradation Of Insulator Insulation Performance?

In the long-term operation of high-voltage transmission systems, the interaction between dirt and moisture on the surface of the high voltage transmission line insulators surface has always been a subject of continuous research in the field of power engineering. The dirt accumulated on the surface of overhead power line insulators can be divided into two categories: soluble dirt and insoluble dirt. The former is characterized by equivalent salt density (ESDD) and is directly related to the change in conductivity of tension insulator. When external humidity conditions are met, these soluble contaminants trigger the electrolyte ionization process, producing a series of chain reactions on the electrical performance of the dead end insulators.

The Influence of Ionization on Surface Conductivity

The chemical composition of contaminants has a significant impact on flashover voltage. Dust containing soluble salts or acid/alkali components has the strongest conductivity and is the type of contaminant that causes the most significant drop in flashover voltage. When fog, dew, or other humid weather occurs, the soluble salts on the dead end suspension insulators surface ionize, and the increased ion concentration directly leads to an increase in surface conductivity, resulting in a surge in leakage current.

This process can be divided into the following stages:

• Initial Dissolution Stage: When contaminant particles encounter moisture, a conductive liquid film forms on the insulator surface, significantly reducing the withstand voltage of the porcelain insulation and drastically lowering the flashover voltage.

• Drying Zone Formation Stage: As leakage current flows on the surface, the contaminant layer is heated unevenly, forming several high-resistance drying zones where the potential gradient rapidly concentrates.

• Partial Discharge Expansion Stage: When the potential gradient of the drying zone exceeds the surface flashover field strength, the discharge energy causes the drying zone to expand further, increasing the leakage current and causing thermal ionization, ultimately forming a discharge channel with arc characteristics.

Potential Risks of Pollution Flashover Accidents

When the conductivity of the accumulated contaminant layer continues to increase, the electric field distribution on the insulator surface becomes severely distorted. Once the electric field strength exceeds the air breakdown field strength (33 kV/cm), a discharge channel forms on the insulator surface, triggering pollution flashover.

The reclosing success rate of pollution flashover accidents is far lower than that of lightning flashovers, often causing large-area, long-term power outages, with losses exceeding those of ordinary lightning strikes. From an operation and maintenance perspective, after several years of repeated accumulation of salt deposits on the surface of insulators through cycles of dirt accumulation and cleaning, the salt deposits tend to reach a saturated salt deposit state. During this stage, the risk of electrolyte ionization remains at a high level for a long period.