Several problems exist in underground distribution networks. The growth of water trees within the groundwall insulation of extruded cables is one of the problems suspected to be the end of life criteria of a cable. A deviee developed at the Institut de recherche d'HydroQuebec(IREQ) attempts to assess the health of the cable insulation. It is a time domain spectrometer (TDS).
The measurements with this unit are influenced by a multitude of parameters. In addition, the aging by water trees is difficult to reproduce in a laboratory due to the very large test objects. Thus, smaller cables with insulation similar to those of the distribution network are more convenient. These miniature cables make it possible to better control each parameter but also to conduct accelerated aging tests.
This research report consists of a parametric study of the dielectric properties of the insulation of miniature cables as a function of aging. The conclusions of this study provide insight into sorne mechanisms of cable aging and they characterize the influence of test parameters on the results from the TDS measurements. The evolution of dielectric properties as a function of aging was measured in several ways. First, the cables are characterized by measurements of dielectric losses then, the performance of insulation is evaluated with the breakdown voltage of the cable. These voltage breakdo\\ns were plotted using the commonly used Weibull distribution. Finally, the length of water trees was measured to determine if a link exists between the length ofthe trees and of the voltage breakdown.
Three types of laboratory aging tests were preformed on the cab les: an aging in water with an altemating voltage applied to the cables, an aging in air with an altemating voltage applied to the cables and finally conditioning in water only. The purpose of this conditioning is to separate the influence of water al one from the process of aging by water trees.
| Date | 5 Jan 2011 |
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| Original language | French |
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| Awarding Institution | - École de technologie supérieure
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| Supervisor | Éric David (Supervisor) & Jean-Luc Parpal (Co-supervisor) |
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Bernier, S. (Author),
David (Supervisor) & Parpal (Co-supervisor),
5 Jan 2011Student thesis: Master's thesis › Master in Engineering: Electrical Engineering