AC filter is the key equipment to improve the power quality in UHVDC transmission project

but it often causes frequent fault due to improper production process and other reasons.In this paper

a tripping fault of AC filter capacitor at an UHV converter station is analyzed deeply.The influence by the operating overvoltage

closing inrush current and harmonics are eliminated through appearance inspection

electrical detection

disassembly analysis

oil chromatogram and fault recording of the faulty capacitor

thinking that the main cause of this fault is the poor welding process of the lead wire and the core of the capacitor.Three spare capacitors of the same batch are selected for the test of withstanding voltage

partial discharge

24-hour rated current;short-circuit discharge and disassembly

judging that the defect is not a family defect

but accidental one.Finally

the corresponding preventive measures and suggestions are proposed for the fault so to improve the operation reliability of the converter station filter banks.