During extended periods of rain or high humidity, surge arresters in power systems face significant operational challenges. Dampness itself is not the direct cause of failure, but it critically exacerbates two primary risks: pollution flashover on the external insulation surface and potential internal moisture ingress. When rainwater mixes with contaminants like industrial dust or salt accumulated on the insulator sheds, it can form a conductive layer. This increases leakage current and may lead to partial arcing, potentially developing into a surface flashover that threatens grid stability. The more critical risk is internal. If the arrester's sealing is compromised due to long-term service or material aging, moisture can permeate the housing. This causes the core metal oxide varistor (MOV) blocks to become damp, degrading their non-linear voltage-current characteristics. Consequently, the resistive leakage current under operating voltage can rise abnormally, leading to continuous heat generation. In severe cases, this can result in thermal runaway, causing internal breakdown or explosion.
Therefore, maintenance efforts must be intensified before and during the wet season. A key focus is close monitoring of operational status. Many modern arresters are equipped with online monitoring devices that provide real-time data on total leakage current and its resistive component. Maintenance personnel should pay particular attention to trends in the resistive current, as it is a crucial indicator of MOV aging or internal moisture. A sustained and significant increase, even if within absolute limits, should be treated as a serious warning. Additionally, using infrared thermography for comprehensive inspections after rain or during high humidity is an effective method for detecting anomalies. A noticeably higher temperature on one section or part of an arrester compared to others under similar conditions may indicate an internal defect or severe surface contamination causing abnormal localized current.
Targeted preventive measures are equally essential. For arresters operating in heavily polluted areas (e.g., industrial or coastal zones), a thorough cleaning before the rainy season is highly recommended. For critical equipment, applying a specialized anti-pollution flashover coating (such as RTV silicone rubber) to the clean, dry insulation surface can be beneficial. This coating provides excellent hydrophobicity, preventing water from forming a continuous film and significantly raising the flashover voltage. Furthermore, regular checks of seal integrity should not be neglected, especially for older equipment, focusing on sealing conditions at flange joints and pressure relief diaphragms. Fundamental maintenance also includes ensuring ground leads are securely connected and free from corrosion, and that drainage around the equipment base is clear to prevent water accumulation.
The effectiveness of a robust moisture protection strategy is reflected in several concrete indicators: the equipment appears clean with no signs of abnormal discharge or arcing; online monitoring data is stable and balanced across phases without upward trends; infrared scans show even temperature distribution without hot spots; and ancillary devices like discharge counters function correctly. By adopting this data-driven, seasonal-focused preventive maintenance approach, surge arresters can be ensured to remain reliably operational through damp and harsh weather, steadfastly guarding the insulation safety of the power grid.