Electrical treeing characteristics in XLPE power cable insulation in frequency range between 20 and 500 Hz

Sch. of Electron. & Comput. Sci., Univ. of Southampton, Southampton
IEEE Transactions on Dielectrics and Electrical Insulation (Impact Factor: 1.28). 03/2009; 16(1):179 - 188. DOI: 10.1109/TDEI.2009.4784566
Source: IEEE Xplore


Electrical treeing is one of the main reasons for long term degradation of polymeric materials used in high voltage AC applications. In this paper we report on an investigation of electrical tree growth characteristics in XLPE samples from a commercial XLPE power cable. Electrical trees have been grown over a frequency range from 20 Hz to 500 Hz and images of trees were taken using CCD camera without interrupting the application of voltage. The fractal dimension of electric tree is obtained using a simple box-counting technique. Contrary to our expectation it has been found that the fractal dimension prior to the breakdown shows no significant change when frequency of the applied voltage increases. Instead, the frequency accelerates tree growth rate and reduces the time to breakdown. A new approach for investigating the frequency effect on trees has been devised. In addition to looking into the fractal analysis of tree as a whole, regions of growth are being sectioned to reveal differences in terms of growth rate, accumulated damage and fractal dimension.

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Available from: George Chen, Feb 03, 2015
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    • "Numerous researches have been conducted to characterize the shapes of these micro-structures (trees) [1] [2]. So, the propagation of these later and the breakdown mechanisms as well as the time lags to breakdown have been studied by many investigators such as Zheng [2], Dissado [3] and Chen [4]. A relationship between these characteristics and the experimental parameters (electrical, thermal, geometrical, chemical, mechanical …) has been reported in references [5- 9]. "
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    ABSTRACT: This paper presents a physico-chemical experimental study of treeing structures expanding in EPDM (Ethylene Propylene Diene Monomer) in a point - plane electrode geometry. Accelerated electrical degradation tests, under alternating 50 Hz electrical field, were realised on this polymer to initiate trees and to follow their propagation (i.e. the tree length) by measuring the partial discharges (PDs) occurring within this insulating material. A chemical analysis by Scanning Electron Microscopy (SEM) and by Infrared spectroscopy (IR) are undertaken to determine the damaged polymer microstructures and changes in its morphology. The chemical groups existing in this material and the changes due to its degradation under electrical field have been identified by Infrared spectroscopy. The microstructure modification of this material, by breaking chemical bonds and splitting molecular chains, explains the formation of tree channels, and accompanying off-gases that promote the appearance of partial discharges and develop the defect. This process is related to the amplitude and the duration of the electrical field which governs the tree forms and which depends on the diameter of the channels and their internal texture revealed by SEM analysis.
    IEEE Transactions on Dielectrics and Electrical Insulation 10/2013; 20(5-5):1577-1583. DOI:10.1109/TDEI.2013.6633686 · 1.28 Impact Factor
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    • "Numerous papers have been published investigating various electrical treeing parameters in polymeric insulating material [1] [2] [3] [4] [5]. Such parameters include tree inception voltage, tree breakdown voltage, tree length, tree inception time, tree breakdown time, fractal dimension and number of branches. "
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    ABSTRACT: This paper presents a statistical approach to analyze electrical tree inception voltage, electrical tree breakdown voltage and tree breakdown time of unsaturated polyester resin subjected to AC voltage. The aim of this work was to show that Weibull and lognormal distribution may not be the most suitable distributions for analysis of electrical treeing data. In this paper, an investigation of statistical distributions of electrical tree inception voltage, electrical tree breakdown voltage and breakdown time data was performed on 108 leaf-like specimen samples. Revelations from the test results showed that Johnson SB distribution is the best fit for electrical tree inception voltage and tree breakdown time data while electrical tree breakdown voltage data is best suited with Wakeby distribution. The fitting step was performed by means of Anderson-Darling (AD) Goodness-of-fit test (GOF). Based on the fitting results of tree inception voltage, tree breakdown time and tree breakdown voltage data, Johnson SB and Wakeby exhibit the lowest error value respectively compared to Weibull and lognormal.
    Journal of Electrical Engineering and Technology 07/2013; 8(4):840-849. DOI:10.5370/JEET.2013.8.4.840 · 0.53 Impact Factor
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    • "Thus bush trees may extend more slowly than branch trees even though they are produced at higher voltages because they possess a higher damage density expressed by a higher fractal dimension [1] [6]. Recently trees possessing more complicated shapes that have been termed 'stagnated' (tree apparently ceases to grow) [11] and 'monkey-puzzle' [12] [13] or 'branch-pine' [14] (exhibiting many short side branches on each side of the long branches) have been noted to occur in both polyethylene and epoxy resins. It is possible that the more complex electrical tree shapes such as these may influence the relationship between tree extension rate and tree shape previously found for simple fractal trees. "
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    ABSTRACT: The results of an investigation into electrical tree growth in XLPE cable insulation using an embedded needle electrode are reported for a range of voltages from 9 kV rms to 27 kV rms. The partial discharge (PD) activity and tree structures were measured simultaneously throughout the tree growth and the trees were recorded from initiation up to and including the final runaway stage. A multifractal analysis was also performed on the tree structures as they propagated, and it was found that their fractal dimension increased and the distribution of embedded structures changed as small side channels were added to the tree as it grew. At 11 kV rms only branch trees were found and only bush (bush-branch) trees at higher voltages, but at 9 kV rms trees of three different shapes were formed. Observation of the tree shapes at 9 kV rms under reflected light followed by a detailed analysis using con-focal Raman spectroscopy, showed that the stagnated and branch-pine (monkey puzzle) tree shapes were due to the formation of a conducting graphitic deposit upon the walls on tree branches in the region of the needle electrode. This was not present in the branch trees produced at 9 kV rms. A simple scheme is presented for the formation of branch-pine trees and their corresponding PD activity based on the concept of conducting branch generation. The trees produced at 13 kV rms and above have a bush shape, which converts into a bushbranch shape when a runaway branch grows from their periphery. This is shown to happen when the field at the bush tree periphery exceeded a voltage independent critical value, which was estimated to be 100 MV/m. The consequence of this result for the initiation of the runaway stage in branch trees is commented upon.
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