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IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 19, NO. 1, JANUARY 2004 15 Diagnosis of Moisture in Oil/Paper Distribution Cables—Part II: Water Penetration in Cable Insulation–Experiment and Modeling Roberts Neimanis , Member, IEEE , Roland Eriksson , Senior Member, IEEE , and Ruslan Papazyan Abstract— Dynamics of water penetration in mass impregnated cable insulation has been studied. For experimental purposes, arti- ficial damage has been inflicted to a 40-cm-long cable sample and water ingress has been continuously monitored by frequency re- sponse measurements. A similar experiment has been conducted on 2.8-m-long cable sample, where both frequency response and time-domain reflectometry (TDR) measurements have been per- formed. After termination of both experiments, actual moisture content has been measured radially and axially. Based on dielectric measurements, a model of water ingress has been developed and diffusion coefficients have been estimated for mass impregnated cable paper. Index Terms— Dielectric response, Karl Fischer titration, mass impregnated cable, moisture content, oil paper insulation. I. INTRODUCTION I NCREASED moisture in cable systems can be caused in joints due to improper or deteriorated sealing. Also, the lead sheet of the cable can be deteriorated due to corrosion or me- chanical damage. Such defects may eventually lead to insula- tion failure. In an accompanying paper, Part I, [8], the problem of moisture in oil paper cables has been studied and a method de- veloped to determine the average moisture content by dielectric spectroscopy (i.e., measurement of dielectric losses and capaci- tance in the frequency range 0.001–1000 Hz). The method gives information on an average value of the moisture content for the whole cable but cannot directly be used to distinguish between short sections of a cable that are wet. Nor can it identify where these sections are located. In this paper, moisture ingress and diffusion in oil paper ca- bles are studied. Pieces of a cable taken from service have been used where a 4-mm cut in the lead sheath has been made. This part of the cable has then been immersed in water for periods up to 600 h. During the wetting process, dielectric spectroscopy and time-domain measurements were made. The results show that the moisture ingress has a consider- able influence upon both the dielectric losses as function of fre- quency- and the time-domain reflectometry measurements. After completion of the experiments, the cable has been desiccated and the moisture content measured radially and Manuscript received December 7, 2001. R. Neimanis is with Programma Electric AB, Täby SE-187 75, Sweden (e-mail: [email protected]). R. Eriksson and R. Papazyan are with the Royal Institute of Tech-
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