A Study on Detection of Weak X/&lt;i&gt;γ&lt;/i&gt;-ray with Growth of Water Trees

Electrical Engineering Japan

2015

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SUMMARYBow-tie trees (BTTs) generated by contaminants, for example, metal, amber (overcured resin), carbon, and voids in the insulators of XLPE (cross-linked polyethylene) cables still remain a factor contributing to deterioration. In order to examine the influence of contaminants on the behavior of BTT generation, we performed several experiments using XLPE samples containing copper powder, finely divided overcured resin, or micro voids as BTT nuclei. As a result of the experiments, in spite of the great difference in the distribution of particle diameter, and the shape and permittivity of the nuclei, all samples containing copper powder or overcured resin showed a common dependence of the number of BTTs on the mean size of the BTT nuclei. Consequently, there is no fundamental difference in these nuclei. We consider that the lower limit of the nucleus size suitable for BTT generation is determined by the local electric field at the tip of the nuclei and its upper limit is determined by the extent of stagnation of ions around the nuclei. Moreover, we consider that the increase in the mean size of BTTs with the initial water content was caused by relaxation of the local electric field due to absorbed water in XLPE samples. C⃝ 2015 Wiley Periodicals, Inc. Electr Eng Jpn, 191(3): 1-8, 2015; Published online in Wiley Online Library (wileyonlinelibrary.com).

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Section: Effect Of Nucleus Sizementioning

confidence: 99%

Experimental Study on Dependence of Bow‐Tie Trees on Nuclei

Electrical Engineering Japan

2015

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“…In addition, we reported the detection of weak X/γ radiation in submersion experiments with XLPE samples . This radiation attenuates for several hours after the completion of submersion experiments, and depends on the type and diffusion profile of metal ions in the water used for submersion . A direct relationship between the initiation and development of water trees and radiation has not been yet established but there is a possibility that some unknown reactions occur at the atomic nucleus level in the XLPE bulk without the participation of oxygen.…”

Section: Introductionmentioning

confidence: 99%

Low Participation of Oxygen in the Generation and Progression of Bow‐Tie Trees

Electrical Engineering Japan

2014

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SUMMARY Bow‐tie trees (BTTs) generated by microscopic contaminants or voids in insulators of cross‐linked polyethylene (XLPE) cables still remain a factor contributing to deterioration. It has been reported that redox reactions of ions diffusing in XLPE lead to molecular chain cleavage. In such an electrochemical mechanism, the participation of oxygen in addition to ions is suspected. In order to examine the influence of oxygen on BTT generation and progress, we performed various experiments controlling oxygen gas by vacuum degassing, a gas barrier film, and so on. The number of BTTs and the maximum BTT length of XLPE samples aged at 60 °C increased with the water content. However, several of the data deviated significantly from these relationships. These results indicate that BTT generation and progression were promoted by vacuum degassing and inhibited by wrapping the samples with a gas barrier film or bubbling air through tap water to immerse the samples. On the whole, the behavior of BTT generation toward supplying or shielding of oxygen was not consistent. The experimental results can be qualitatively explained by diffusion or permeation of ions and water rather than oxygen gas, and thus oxygen seems not to be directly associated with BTT generation and progress.

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A Study on Low Participation of Oxygen in Generation and Progress of Bow-tie Trees

2013

IEEJ Trans. FM