Capacitance corrections for guard gaps

Goad, D. G. W.; Wintle, H. J.

doi:10.1088/0957-0233/1/9/020

Cited by 14 publications

(10 citation statements)

References 7 publications

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“…In 1990, capacitance corrections for guard gaps were summarised by Goad and Wintle [13] and its close-form representation provides a good overview including several valuable corrections and further analytical expansions in order to avoid implicit calculations. Furthermore, in [13], it was concluded that the fringing parameter is only minor affected by electrode thickness. Moreover, computational calculations are presented considering different permittivities for the test sample and the gap of the guard ring setup and recommendations focusing on capacitance measurements are provided.…”

Section: Field Distribution In Guarded Electrode Setupsmentioning

confidence: 99%

“…The work of Endicott [12] in 1976 is fostering the results presented above, whereas especially for implicit equations, expansions are provided in order to allow direct calculations. In 1990, capacitance corrections for guard gaps were summarised by Goad and Wintle [13] and its close‐form representation provides a good overview including several valuable corrections and further analytical expansions in order to avoid implicit calculations. Furthermore, in [13], it was concluded that the fringing parameter is only minor affected by electrode thickness.…”

Section: Conductivity Measurement: Setups Fringing Effects and Inmentioning

confidence: 99%

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Model‐based accuracy enhancements for guarded conductivity measurements: determination of effective electrode areas utilising numerical field simulation

Freye

Jenau

2018

High Voltage

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Methods utilising current measurements for conductivity and permittivity determination require precise knowledge of the effective electrode area in order to obtain accurate results. Owing to field distortions (e.g. caused by fringing) in guarded electrode setups, the effective electrode area differs significantly from the geometrical calculated. Focusing on guarded electrode setups for conductivity determination, a generic method based on numerical field simulation is presented allowing a convenient determination of the relevant effective electrode area. For this purpose, a brief overview of yet existing normative guidelines and related research work is provided. State-of-the-art conductivity measurement setups are presented in order to identify parameters which affect the field distribution within the measurement arrangements. The description of the implemented method and its realisation in COMSOL multiphysics is followed by its validation using analytical fringing calculations. Furthermore, presented method is used for the evaluation of fringing effects and additional field distortion caused by design aspects of the measurement cell itself and potential imbalances related to the measurement setup. Moreover, dependencies on conductivity of the surrounding environment are considered. Achieved model-based accuracy enhancements are calculated and are leading to a gain in precision for conductivity determination of up to 25% compared to yet existing approaches.

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Section: Field Distribution In Guarded Electrode Setupsmentioning

confidence: 99%

Section: Conductivity Measurement: Setups Fringing Effects and Inmentioning

confidence: 99%

Model‐based accuracy enhancements for guarded conductivity measurements: determination of effective electrode areas utilising numerical field simulation

Freye

Jenau

2018

High Voltage

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“…This effective area of the measuring electrode is actually larger than its geometrical surface due to the edge fringing effect. The effective radius of the measuring electrode has been well investigated and several correction expressions have been obtained [3][4][5][6][7][8][9]. Thomson used conformal transformation to obtain the field distribution in a guarded electrode system [3].…”

Section: Introductionmentioning

confidence: 99%

“…Amey calculated an effective radius under the condition that the permittivity of the sample is much higher than that of air [6]. Goad and Wintle reviewed the equations for the guard gap correction and evaluated the validity of these equations in capacitance measurement [7]. Lisowski and co-workers have derived correction expressions when the sample's permittivity is not high and proposed advice to IEC 60093 [8,9].…”

Section: Introductionmentioning

confidence: 99%

Study of a guarded electrode system in the dc conductivity measurement of insulating liquid

Zhou

Hao

Wilson

et al. 2014

Meas. Sci. Technol.

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The design and choice of an electrode system is important in dc conductivity measurement of insulating liquid. In this paper, the electric field distribution of an electrode system which consists of two parallel circular metallic electrodes and a guard electrode has been studied using Comsol Multiphysics software. A new parameter, which is not yet involved in current standards, the edge radius, has been mentioned in the literature formerly and is currently discussed in a CIGRE working group. In this paper, the influence of this parameter has been investigated by means of field calculation. As seen from the simulating result, there are regions in the vicinity of the edges of the guard and measuring electrode that are under high electric field. If the edges of these two electrodes are sharp, the maximum electric field in the test cell will be much higher than the average field between the measuring electrode and the high voltage electrode. An empirical equation has been proposed to calculate this maximum field. The classic correction expression for an effective radius has been re-evaluated with the edge radius being taken into account. Experimental work has been performed to confirm this conclusion. Three kinds of mineral oils with different ageing times have been tested under the dc field using a guarded electrode system and the electric strengths of these oils have been estimated. A recommendation has been made to current standards in insulating liquid measurement.

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“…Researchers were struggling with accuracy in capacitance determinations for more than a century [4][5][6]. In general, there are two suggested methods to limit this effect, one is to use a guard ring which confines the effective measured area [7]; another one is to compensate the measured capacitance with a correction factor by either analytical calculations or numerical estimations [6,8]. Dielectric response, in application of high voltage engineering, is often measured from a high impedance current shunt [3] and resulting in non-negligible voltages generated at the measuring electrode.…”

mentioning

confidence: 99%

Correction of Geometric Influence in Permittivity Determination

Xu¹,

Bengtsson²,

Blennow³

et al. 2018

NORD-IS

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Determination of relative permittivity of dielectric materials is generally done with a rather low accuracy, in the order of several percent. This is in a sharp contrast to the accuracy of measurements of the dissipation factor, both usually being determined in the same measurement. A common understanding for the inferior accuracy in permittivity measurements is the effects of electrode edges. However, further studies indicate that geometric effects, arising from electrode shielding box, guard ring, electrode supporting materials, etc., also influence the accuracy significantly if the responding voltage present at the measuring electrode is non-negligible. With help of the Finite Element Method (FEM), geometric correction factors are estimated from an electrode model to increase the accuracy. This study is specially focused on the application of contact-free electrode arrangement using the air reference method. In this paper, a few examples of how geometric influences affect results are presented as well as a comparison of experimental results. From these insights, we discuss how to minimize and compensate the geometric effects.

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Capacitance corrections for guard gaps

Cited by 14 publications

References 7 publications

Model‐based accuracy enhancements for guarded conductivity measurements: determination of effective electrode areas utilising numerical field simulation

Model‐based accuracy enhancements for guarded conductivity measurements: determination of effective electrode areas utilising numerical field simulation

Study of a guarded electrode system in the dc conductivity measurement of insulating liquid

Correction of Geometric Influence in Permittivity Determination

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