Abstract: This article provides a detailed analysis of an abnormal secondary measurement voltage fault in a 110 kV capacitive voltage transformer (CVT). Through capacitance and dielectric loss factor testing, as well as insulation oil chromatography testing, it was found that the main insulation of the C-phase CVT was abnormal, manifested as excessive capacitance change rate and insulation oil degradation. After disassembly inspection, it was confirmed that some capacitor units of the C-phase CVT voltage divider capacitor C2 had breakdown. The cause of the fault was poor voltage connection and low cleanliness during the manufacturing process, burrs, and foreign objects causing high local field strength during operation, ultimately leading to breakdown. This article proposes strict implementation of the initial inspection test cycle for newly put into operation CVTs, focusing on sampling and witnessing partial discharge tests of CVTs before leaving the factory, and strengthening live detection to prevent similar faults from occurring.