Research on Aging Evaluation Indexes of Cooling Water Sealing Rings in HVDC Converter Valves

The EPDM rubber sealing rings are very important for the safe operation of the high voltage direct current converter valves. The conclusions of aging life in references can't be used to effectively plan the maintenance strategy under a complex cooling water environment. Based on the test and analysis results of the physical parameters of the field operated sealing rings, the aging evaluation indexes and maintenance strategy are proposed for the first time. Operated sealing rings with different operating years from 7 different converter stations are collected. The compression set, surface and cross‐section morphology, element content and infrared spectrum of the sealing rings were measured. The results show that the compression set increases monotonically with operating time. It is recommended to replace the sealing rings when the compression set reaches 24%, and the sealing is considered to have failed when it reaches 28%. Compression set is suggested as the primary indicator for aging assessment. As the compression set increases, the surface oxygen content gradually increases; the surface methylene index decreases monotonically. The surface oxygen content, methylene index, carbon–carbon double bond index, and carbon–oxygen single bond index can all serve as auxiliary aging indexes for evaluation of sealing ring aging condition.