Anti-pollution Flashover Technology and Fault Detection Methods for High Voltage Insulators

Pollution flashover is one of the most common fault types of high voltage insulators, which may lead to large-scale power outages once it occurs. Understanding the pollution flashover mechanism, mastering anti-pollution flashover measures and fault detection technologies are indispensable capabilities in power operation and maintenance.

I. Pollution Flashover Fault Mechanism

1. Pollution Flashover Formation Process

The formation of pollution flashover generally goes through four stages:

1. Pollution Accumulation: Salt spray, industrial dust, cement ash and other pollutants in the air gradually deposit on the insulator surface
2. Moisture Absorption: Under humid weather conditions such as heavy fog, drizzle or condensation, the pollution layer absorbs moisture to form a conductive film
3. Leakage Current Increase: The conductive film causes a sharp increase in leakage current on the insulator surface, producing localized heating
4. Flashover: When the leakage current density exceeds the critical value, localized dry-band breakdown rapidly develops into surface flashover

2. Hazards of Pollution Flashover

• Causes line tripping and large-scale power outages
• In severe cases, may cause insulator rupture or conductor burnout
• Concentrated outbreaks during heavy fog or drizzle weather, affecting wide areas
• Low reclosing success rate (due to unrecovered insulation)

II. Anti-pollution Flashover Technical Measures

1. Increase Creepage Distance

Select insulators with appropriate specific creepage distance according to the pollution level of the operating environment. In heavy pollution areas (Class IV), anti-pollution products with specific creepage distance ≥31mm/kV should be selected. By increasing the number of sheds or adopting large creepage distance structures, the leakage distance is significantly extended.

2. RTV Coating Spraying

RTV (Room Temperature Vulcanized Silicone Rubber) coating is one of the most effective anti-pollution flashover measures. After spraying RTV coating on the insulator surface, a silicone rubber coating with excellent hydrophobicity is formed, which can increase the pollution flashover voltage by 2-3 times. RTV coating also has hydrophobicity transfer characteristics - even if the surface is covered with pollution, the low molecular weight siloxane of the silicone rubber will still migrate to the surface of the pollution layer, maintaining hydrophobicity.

3. Select Composite Insulators

Silicone rubber composite insulators themselves have excellent hydrophobicity and anti-pollution flashover performance, and are preferred in new lines in heavy pollution areas. However, attention should be paid to the decline in hydrophobicity after several years of operation, and HC value should be tested regularly.

4. Live-line Cleaning

For insulators in heavy pollution areas with salt density ≥0.2mg/cm2, live-line cleaning robots or live-line water washing can be used to remove surface pollution and restore insulation level.

III. Fault Detection Technologies

1. Infrared Thermography Detection

If insulators in operation have local defects (such as internal cracks, zero-value insulators, etc.), abnormal temperature distribution will occur. Infrared thermal imagers can detect temperature anomalies remotely and non-contact, quickly locating problem insulators. Temperature differences exceeding 1K should be noted.

2. UV Imaging Detection

When corona discharge or partial discharge occurs on the insulator surface, ultraviolet light is generated. UV imaging cameras can visualize UV signals, intuitively displaying the discharge location and intensity. No obvious UV discharge should occur during normal operation; if continuous discharge signals are detected, timely maintenance should be arranged.

3. Voltage Distribution Measurement

For insulator strings, the distribution voltage of each insulator unit can be measured to determine whether there are zero-value or low-value insulators. When the voltage of a single insulator unit is lower than 20% of the normal value, it is judged as low-value; when lower than 5%, it is judged as zero-value. Zero-value insulators should be replaced as soon as possible.

4. Hydrophobicity Test (Composite Insulators)

Conduct hydrophobicity classification tests on composite insulators according to DL/T 864 standard. HC1-HC3 are qualified; HC4-HC5 indicate significant decline in hydrophobicity, requiring enhanced monitoring or replacement.

5. Drone Image Recognition

In recent years, rapidly developing drone inspection combined with AI image recognition technology can automatically identify abnormal conditions such as insulator damage, shed cracking, and pollution level without climbing poles, greatly improving inspection efficiency.

IV. Comprehensive Prevention Strategies

• Regional Pollution Level Classification: Establish line corridor pollution distribution maps to guide insulator selection and cleaning cycles
• Differentiated Operation and Maintenance: Adopt different inspection and cleaning frequencies for heavy pollution areas and general areas
• Condition-based Maintenance Transition: Transition from regular maintenance to condition-based maintenance based on equipment status
• Full Lifecycle Management: Full process management from manufacturing quality control to operation monitoring to retirement and replacement

Anti-pollution flashover work is a systematic project that requires comprehensive measures combining environmental conditions, equipment characteristics and detection technologies to effectively reduce the pollution flashover trip rate and ensure the safe and stable operation of the power grid.