Modeling and Measurements of Electric Fields in Composite Oil/Cellulose Insulation

Gäfvert, U.; Hjortstam, Olof; Serdyuk, Yuriy V.; Törnkvist, C.; Walfridsson, Lars

doi:10.1109/ceidp.2006.312084

Cited by 16 publications

(8 citation statements)

References 6 publications

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“…The model used in the present work is similar to that described in [5,6] and it is outlined below. In the study, cylindrical coaxial electrodes with radiuses 30 mm (inner electrode) and 32 mm (outer electrode) forming 2 mm thick oil gap are considered.…”

Section: The Ion Drift Modelmentioning

confidence: 98%

Measurements of ion mobility in transformer oil: Evaluation in terms of ion drift

Hjortstam¹,

Schiessling²,

Serdyuk

et al. 2012

2012 Annual Report Conference on Electrical Insulation and Dielectric Phenomena

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The aim of this paper is to develop a theoretical foundation of the reversed polarity method for measuring the mobility of ions in transformer oil. The results of the measurements of transient currents in oil, showing very distinct transient current peaks appearing after polarity reversal, are evaluated by computer simulations using an ion drift model. It is found from the analysis that the peaks in the measured currents occurred at instants much shorter than the so-called transit time that is the time for an ion to cross the oil gap between electrodes. A relation between the transit time and the current peak position is found that can be used to extract the ion mobility from data obtained with an experimental set up in which the transit time is shorter than the dielectric relaxation time of the liquid. On the other hand, for a setup providing the dielectric relaxation time shorter than the transit time, the current peak position strongly depends on the former and no simple correlation between the current peak position and transit times can be established.

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Section: The Ion Drift Modelmentioning

confidence: 98%

Measurements of ion mobility in transformer oil: Evaluation in terms of ion drift

Hjortstam¹,

Schiessling²,

Serdyuk

et al. 2012

2012 Annual Report Conference on Electrical Insulation and Dielectric Phenomena

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“…The ion drift model is described in [2,3] and can be used to describe oil under DC stress. In this case only the oil is considered.…”

Section: The Ion Drift Modelmentioning

confidence: 99%

“…Particular for the electrical insulation design of the valve side winding is the need to withstand both AC and DC electrical stress requiring knowledge of the (high field) resistivity of all materials involved. The most challenging material involved here is the mineral oil due to its strongly nonlinear dependents of the resistivity on electric field due to its ionic nature [1][2][3][4].…”

Section: Introductionmentioning

confidence: 99%

Modelling and measurement of field dependent resistivity of transformer oil

Lavesson¹,

Walfridsson²,

Hjortstam³

et al. 2014

2014 IEEE 18th International Conference on Dielectric Liquids (ICDL)

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This article studies the apparent resistivity of mineral oil as a function of electric DC stress using theoretical and experimental methods for three different oils. The experimental measurement of the apparent resistivity is done using a cell with two bare Rogowski like electrodes separated by a 2mm gap. The dc current is measured after one hour and the stress is varied in steps. For low DC stress the apparent resistivity rises with increasing voltage, leveling off and dropping slightly for higher voltages. The resistivity is modeled using the ion drift model with equilibrium resistivity measured using dielectric response as input. The charge dynamics and the corresponding resistivity is simulated and the results compared with the measured values. The main features seen in the measurements are captured in the simulation and there is a good overall agreement between the theoretical data and the experimental values.

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“…The model used in this article is similar to that described in [2,3] and it is outlined below. The ion drift model described below is implemented and solved in the simulation finite-element software Comsol Multiphysics V4.3 [6].…”

mentioning

confidence: 99%

“…From the literature it is clear that the ionic transports in the insulation liquids have to be taken into account in order make good predictions of the electrical field distribution under voltage stress. The so called ion-drift models have been discussed by several authors during the past decades [1][2][3]. Such models include dissociation of ions from pre-existing ion pairs as well as transport of ions in electrical field.…”

mentioning

confidence: 99%

Comparison of simulated and measured field dependent charge injection in mineral oil under dc bias

Hjortstam¹,

Sonehag²,

Schiessling³

2018

NORD-IS

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The present study aims at the understanding of charge injection from metal electrodes into mineral oil under DC stress. The work focuses on the field dependence of the charge injection. In a previous article the electrical field in a blank oil gap with parallel electrodes is measured with a so called Kerr electro-optic technique. The data show that the electrical field is close to symmetric for low fields (~ 0.1 kV/mm) but strongly asymmetric at higher fields (~ 1 kV/mm). In the present study an ion drift model is used to analyze the data. We show that an ion drift model including a field dependent injection term can reproduce the measured results fairly well. Furthermore, the comparison of measured and simulated results shows that the charge injection is stronger from an electrode with positive polarity compared to one of negative polarity.During the last years it has been a push for Ultra High Voltage Direct Current (UHVDC) transmission systems, due to the rising demands on transmitting electrical power over long distances. A key component in such systems is the mineral oil insulated HVDC converter transformer. The increased voltage levels are calling for a deeper understanding of high field phenomena under dc stress in mineral oil based insulation systems.

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Modeling and Measurements of Electric Fields in Composite Oil/Cellulose Insulation

Cited by 16 publications

References 6 publications

Measurements of ion mobility in transformer oil: Evaluation in terms of ion drift

Measurements of ion mobility in transformer oil: Evaluation in terms of ion drift

Modelling and measurement of field dependent resistivity of transformer oil

Comparison of simulated and measured field dependent charge injection in mineral oil under dc bias

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