Views: 0 Author: Site Editor Publish Time: 2026-07-21 Origin: Site
Zinc oxide surge arresters are widely deployed in power systems owing to their excellent nonlinear volt-ampere characteristics, high current-carrying capacity, and simple structure. Nevertheless, long-term field operation frequently exposes them to harsh environmental conditions. Moisture intrusion—typically arising from aged sealing rings, defective end-cap interfaces, or manufacturing process deficiencies—progressively degrades the electrical properties of ZnO varistors. Domestic statistics indicate that the average failure rate of operating zinc oxide surge arresters is approximately 0.286 per hundred phase-years. Among all failure modes, dampness-induced insulation deterioration is consistently identified as the most frequent and insidious cause.
The interface between the composite housing and metal end cap represents the primary weak point in sealing integrity. Temperature cycling and mechanical vibration during operation create differential thermal expansion between silicone rubber and metal components, potentially generating micron-sized gaps. Once such gaps develop, rainwater and water vapor can penetrate the arrester interior through capillary action in high-humidity environments. Accumulated moisture at the bottom corrodes metal fittings, deteriorates insulating support components, and creates conductive films on valve plate surfaces. This alters the ZnO varistor characteristics, causing progressive increase in resistive leakage current, ultimately leading to thermal runaway and catastrophic failure.
A tiered diagnostic approach is essential for early detection of moisture-related defects without service interruption.
3.1 Infrared Thermography (Initial Screening)
Infrared thermography serves as the first-line screening tool. During normal operation, MOA internal power dissipation generates heat; moisture ingress increases resistive current and consequently elevates operating temperature. In one documented 110 kV case, infrared inspection revealed a C-phase arrester at 18.4°C versus 16.6°C for the healthy B-phase—a 1.8 K differential classified as a critical defect. While infrared thermography is effective for rapid, measurement results are influenced by distance, angle, and ambient conditions, necessitating confirmatory testing.
3.2 Resistive Leakage Current Measurement (Confirmation)
Resistive leakage current is the most sensitive indicator of internal moisture. Under normal conditions, the resistive component should constitute no more than 20% of total leakage current. In the aforementioned case, the C-phase resistive current was 11.37 times that of the A-phase and 9.39 times that of the B-phase. Longitudinal comparison showed a 12.7-fold increase over eight months. Industry guidelines mandate outage inspection when resistive current doubles.
3.3 Online Monitoring Systems (Continuous Surveillance)
Modern online monitoring systems integrate leakage current sensors with harmonic analysis using FFT to extract resistive fundamental and third-harmonic components. Third-harmonic leakage current analysis has proven particularly sensitive for early moisture detection. Advanced implementations incorporate internal temperature and humidity sensors for comprehensive condition assessment. These systems enable real-time data acquisition without service interruption.
3.4 Integrated Diagnostic Protocol
A three-stage diagnostic protocol is recommended: infrared thermography for initial screening; resistive leakage current measurement for confirmation; and DC leakage testing during scheduled outages for definitive diagnosis. This integrated approach mitigates the risk of false positives from electromagnetic interference and environmental factors.
4.1 Material and Manufacturing Controls
Sealing integrity begins at the manufacturing stage. Strict sealing tests must be conducted before arrester deployment. Valve plates require thorough drying during assembly, as incomplete drying introduces internal moisture. Production environment humidity must be rigorously controlled.
4.2 Advanced Sealing Structure Design
Double sealing configurations incorporating O-rings and leak-proof rings at cover plate interfaces, combined with U-shaped sealant storage tanks, significantly enhance long-term reliability. The sealant storage not only absorbs mechanical stress but also automatically compensates for compression as seals age. Hydrophobic coatings applied to core insulation shells eliminate interface gaps, blocking moisture infiltration at the source. Optimized flange drainage structures with drain holes prevent water retention even when minor condensation or seal leakage occurs. Double-layer sealing systems filled with high-purity nitrogen further prevent oxidation and moisture contamination.
4.3 Operational Maintenance Practices
Post-installation, regular inspections—particularly after thunderstorms—are essential for early anomaly detection. Online leakage current meters should be continuously monitored. Preventive testing schedules must incorporate both online monitoring and periodic offline diagnostic measurements.
Moisture ingress in zinc oxide surge arresters, primarily caused by sealing degradation, represents a critical threat to power system reliability. The diagnostic framework presented—integrating infrared thermography for screening, resistive leakage current measurement for confirmation, and online monitoring for continuous surveillance—enables early detection without service disruption. The comprehensive prevention strategy encompassing manufacturing quality control, advanced sealing design, and diligent operational maintenance provides a systematic approach to mitigating moisture-related failures. Implementation of these measures will significantly enhance MOA operational reliability and extend service life.
