Abstract：This paper investigates a secondary voltage anomaly fault in a 220 kV capacitive voltage transformer (CVT). Through comprehensive analysis of test data and post-disassembly internal inspections, the root cause is identified as moisture ingress into the electromagnetic unit, which degrades insulation performance and ultimately leads to insulation breakdown under sustained electric field stress. Notably, the defect is deeply embedded within the electromagnetic unit, evading detection by conventional preventive testing protocols such as dielectric dissipation factor measurements. This case study proposes structural improvements for manufacturers, including enhanced hermeticity design of electromagnetic units to mitigate moisture penetration risks. Furthermore, it offers actionable insights for grid operators to refine condition assessment frameworks and diagnostic strategies, thereby improving the operational reliability of mission-critical metering devices in power systems. Ensuring the operational reliability performance of capacitive voltage transformer carries significant engineering value.
2025, Vol. 26 
