Electrical stress enhancement of contaminants in XLPE insulation used for power cables

Bostrom, J.-O.; Marsden, E.; Hampton, R.N.; Nilsson, U.H.

doi:10.1109/mei.2003.1226729

Cited by 37 publications

(19 citation statements)

References 4 publications

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“…The permittivity is increased to 2.6 for C1, and increasing to 2.8 and 4.2 for C2 and 3 respectively. The relatively permittivity determined for the sample aged for 340 hours (C3) is significantly higher than previously reported for oxidized XLPE insulation measured at a low voltage [8].…”

Section: A Microscopy Examinationscontrasting

confidence: 60%

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Dielectric properties of organic contaminations in XLPE cable insulation

Hvidsten

Vandbakk²,

Mauseth

2012

2012 Annual Report Conference on Electrical Insulation and Dielectric Phenomena

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Cleanliness is considered as one of the most important factors for ensuring long endurance of HV and EHV XLPE cable insulation. Organic contaminants as oxidized XLPE fragments are difficult to completely remove during cable production. Such contaminants can either origin as inclusions in PE granules or from production of the XLPE cable formed in stagnation zones in the extrusion line. The local AC field enhancement is dependent on the permittivity and the geometry of the contaminant. In addition, it is also likely that voids can be formed close to the inclusions. The main purpose of this work is to determine the dielectric properties of XLPE insulation having the same degree of oxidation as oxidized PE inclusions taken from granules. In this paper, oxidized PE inclusions have been classified in three different categories dependent on their discoloration and further examined by IR spectroscopy and SEM. 250 µm thick XLPE plates have been oxidized up to 340 hours in an oven at 170 °C to reproduce the same magnitude of carbonyl ketonic absorption as determined for the inclusions. The AC dielectric response has been measured using 250 µm thick Rogowski test objects facilitating application of high electric fields. The response has been measured in the frequency range of 1 mHz to 100 Hz at different stress up to 20 kV/mm at ambient conditions. The AC breakdown stress was measured on the same objects. The results show that the permittivity increased with increasing carbonyl content. For the insulation thermally aged for 340 hours, H H' (50 Hz) was close to 4. No significant frequency or field dependence was observed. The calculated AC conductivity increased strongly with carbonyl content, and was in the range of 10 -14 Sm -1 after ageing dependent on the electric stress. The AC breakdown stress was reduced with ageing, especially for the most oxidized samples.

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Section: A Microscopy Examinationscontrasting

confidence: 60%

“…Such sections are likely severely oxidized and mechanically weak. The shapes of the inclusions were characterized by rather sharp edges causing a local high field enhancement in the insulation dependent on the permittivity and conductivity [8].…”

Section: A Microscopy Examinationsmentioning

confidence: 99%

Dielectric properties of organic contaminations in XLPE cable insulation

Hvidsten

Vandbakk²,

Mauseth

2012

2012 Annual Report Conference on Electrical Insulation and Dielectric Phenomena

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“…This has been done for the geometry of an average sample using the finite element based software Comsol Multiphysics with which K was calculated to be 21 mm -1 . The electric field was calculated according to (1) where E is electric field in kV/mm and U is applied voltage in kV.…”

Section: Estimation Of Electrical Field Strengthmentioning

confidence: 99%

“…The quality of the polymer insulation material is a key factor for increasing the voltage rating of power cables and, so far, most of the improvements have been made by reducing the amount of contaminants [1]. Further advancement using this approach is economically and practically challenging as the amount of contaminants in modern superclean polyethylene is extremely low.…”

Section: Introductionmentioning

confidence: 99%

Electrical tree inhibition by voltage stabilizers

Jarvid

Johansson

Englund

et al. 2012

2012 Annual Report Conference on Electrical Insulation and Dielectric Phenomena

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Electrical treeing is one of the main degradation mechanisms in polymer dielectrics at highly divergent electric fields and can, if initiated, cause dielectric breakdown as soon as an electrical tree channel has bridged the insulation. One way of increasing resistance to electrical treeing is the addition of certain organic additives such as polycyclic aromatic compounds or benzophenone-like structures. These additives act as voltage stabilizers that are believed to capture high energy electrons and dissipate their energy, preventing degradation of the polymer matrix by the impact of "hot electrons". In this study, a benzil type compound is evaluated as voltage stabilizer in a superclean cross-linked polyethylene compound used for high voltage cable applications. The stabilizing effect of the additives is measured using test objects of wire-plane electrode geometry in ramped AC voltage experiments. For determining tree initiation conditions, optical detection is used and correlated to voltage measurements. In this way, the initiation voltage of each single tree is determined. Results show that the investigated voltage stabilizer raises the electrical tree inception level significantly. The stabilizing effect is dependent on voltage ramp rate and using a lower ramp rate results in a more pronounced effect of the stabilizer.

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“…This has increased the breakdown strength significantly during the last decades [6]. However, the cleanliness of the material it self and the handling from polymerization to extrusion have been developed to a point where further improvement are costly.…”

Section: Introductionmentioning

confidence: 99%