Metal oxide surge arresters protect power system equipment from lightning and switching overvoltages. MO varistors degrade gradually through thermal runaway and moisture ingress—conditions that online monitoring detects before catastrophic failure.
Leakage Current and Resistive Component
Total leakage current measurement is the simplest monitoring method. Under normal conditions, total leakage is 0.5-2 mA. The resistive component (IR, typically 5-20% of total) indicates varistor degradation. Third harmonic analysis isolates IR from total current using the nonlinear varistor characteristic—a 50% increase in third harmonic signals developing degradation.
Thermal Imaging
Thermal imaging detects hot spots from non-uniform current distribution across parallel varistor columns. Temperature differences exceeding 3°C between columns indicate defective varistors.
Monitoring Equipment
The DT801 Surge Arrester Monitor provides continuous leakage current monitoring. The Smart Grid Platform aggregates arrester data. The Power Grid Monitoring Products cover connected lines. The RMU Integrated Monitor complements arrester protection. The SCYC-HLJC2304 Cable Sheath Monitor detects grounding anomalies.
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