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Dielectric spectroscopy as a condition monitoring technique for cable insulation based on crosslinked polyethylene
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
University of Bologna.
University of Bologna.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
2015 (English)In: Polymer testing, ISSN 0142-9418, E-ISSN 1873-2348, Vol. 44, 135-142 p.Article in journal (Refereed) Published
Abstract [en]

Dielectric spectroscopy was evaluated as a condition monitoring technique for aged polyethylene electrical insulation in nuclear power plants. Bare core insulations of crosslinked polyethylene were aged at 55 and 85 °C under exposure to 60Co γ-radiation at different dose rates (0.42, 0.76 and 1.06 kGy h−1) to different total doses. The samples were studied by dielectric spectroscopy and tensile testing, and the crystallinity, mass fraction of soluble component and density were determined. The oxidation profiles along the depth of the insulations were assessed by infrared microscopy. The aged samples showed an increase in both the real and imaginary parts of the dielectric permittivity over the whole frequency range studied, an increase in the mass fraction of soluble component and in the material density, and a decrease in the strain-at-break. The imaginary part of the dielectric permittivity at 100 kHz increased in a linear fashion with increasing material density, the latter being strictly related to the extent of oxidation of the material according to infrared spectroscopy and differential scanning calorimetry. The generic relationship between the imaginary part of the permittivity and the density included all the data obtained under different ageing conditions. The results suggest that dielectric spectroscopy can be used for in-situ measurements of the degree of oxidation of polyethylene cables, in order to obtain information about the condition of the cable insulation to enable the remaining lifetime to be predicted.

Place, publisher, year, edition, pages
2015. Vol. 44, 135-142 p.
Keyword [en]
Polyethylene, Radiation ageing, Thermal ageing, Dielectric response, Density, Condition monitoring
National Category
Polymer Technologies
Identifiers
URN: urn:nbn:se:kth:diva-168185DOI: 10.1016/j.polymertesting.2015.04.004Scopus ID: 2-s2.0-84928666071OAI: oai:DiVA.org:kth-168185DiVA: diva2:814616
Funder
EU, FP7, Seventh Framework Programme
Note

QC 20150602

Available from: 2015-05-27 Created: 2015-05-27 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Polymeric materials in nuclear power plants: Lifetime prediction, condition monitoring and simulation of ageing
Open this publication in new window or tab >>Polymeric materials in nuclear power plants: Lifetime prediction, condition monitoring and simulation of ageing
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Nuclear power plants generate a significant part of the world’s electrical power consumption. However, many plants are nearing the end of their designed lifetime, and to extend the lifetime it is important to verify that every component can withstand the added service time. This includes polymeric materials, which become brittle with time. By predicting their lifetime and monitoring their condition, unnecessary downtime of the plant can be avoided, and secure operation can be ensured. The lifetime can be predicted by extrapolating results from accelerated ageing to service conditions, or by simulation of the degradation process.

In this study, lifetime predictions through extrapolation were performed on samples of a polyvinyl chloride (PVC) core insulation and an acrylonitrile butadiene rubber (NBR) membrane, which were thermally aged in air. The lifetime of the PVC cable was predicted using Arrhenius extrapolation, and using a method based on Langmuir, Clausius-Clapeyron, and Kirchhoff’s equations.

The lifetime of the NBR membrane was predicted using extrapolation in the temperature domain using an Arrhenius approach coupled with an extrapolation in pressure-domain, yielding realistic lifetimes.

Two cable insulations, one made from crosslinked polyethylene (XLPE) and the other from ethylene propylene rubber (EPR) were aged under the simultaneous effect of elevated temperature and γ-radiation investigated using several condition monitoring techniques. In particular, two non-destructive techniques, dielectric spectroscopy and nuclear magnetic resonance, showed promising results be developed and used in situ.

Finally, a computer model simulating the diffusion and consumption of oxygen in XLPE was developed, based on assumptions that diffusion, consumption and solubility were dependent on the total degree of oxidation. The model showed promise for further development.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. 75 p.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2015:29
National Category
Textile, Rubber and Polymeric Materials
Identifiers
urn:nbn:se:kth:diva-168193 (URN)978-91-7595-587-2 (ISBN)
Public defence
2015-06-11, K2, Teknikringen 28, KTH, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

QC 20150529

Available from: 2015-05-29 Created: 2015-05-27 Last updated: 2015-05-29Bibliographically approved

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