Research Of New Characteristic Parameters For Oil-Paper Aging Used In Transformers

As the main insulation used in oil-immersed transformer, oil-paper suffers fromthermal and electrical aging stress in the long-term running, which deteriorate theinsulating performance and threaten the reliability of transformer directly. Agingresearch work is of vital importance in insulation subject, which contributes to theinsulation diagnosis and lifetime prediction. Especially, with the application ofcomputer technology, insulation diagnosis is experiencing rapid development. There aremany advanced, available and reliable systems are built to identify insulation material'saging conditions, which ensure the security service of high voltage equipments.Ultra wide bind (UWB) frequency partial discharge (PD) test system is designed inthis paper, in which ultra wide bind sensor is compare through simulation wave andpractical measured wave, then white noise is reduced with wavelet analysis technologyto greatly improve Signal-to-Noise without distortion. It is concluded that the designedsystem can satisfy the demand of measuring PD signal in oil-paper aging.The reasonable test condition is chosen to age several oil-paper samples for about400 hours after consult temperature rise of transformers in GB and accelerated ageingtesting program. At the same time, PD wave signal of time domain and frequencydomain is acquired every day, and characteristic parameters are distracted from PDsignal by Matlab software. There are total 19 parameters are extracted and 13 are find tobe closely correlated to aging stages, which are used as aging characteristic parametersin the followed analysis.In order to identify the proper aging condition, fuzzy clustering method is used toanalyze 25 vectors distracted from 5 samples at 5 different aging stages. It is shown thatdifferent samples have the similar performance at the same aging stage. The geometricmeans of every 5 vectors are used to act as representative samples to stand for fiveaging stage. Then membership functions are reasonably chosen which are used tocalculate approach value between samples of every aging time and representativesamples. Aging degree of oil-paper is distinguished through approach value. It isconcluded that a reasonable result can be achieved using the discriminant functions.