The moisture effect on dielectric losses of insulating paper

Bitam-Megherbi, Ferroudja; Osmani, Sharifah Nur Aqilah Wan; Megherbi, Mohammed

doi:10.1109/icsd.2004.1350386

Cited by 11 publications

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“…However, the study of this extreme case can be useful for a good understanding of the phenomena. In addition to the decreasing values of currents with the humidity, corresponding to an increase of material resistivity, the object of an earlier work [2], we noticed a striking difference in shape of the current when the humidity goes from the high values ( lower level of 4.66% (comparatively to level of 6.28%). In the case of 7.6% moisture, Figure 3 shows an important increase but the decrease does not appear, most probably because of the high speed of the decrease phenomenon comparatively to the increase.…”

Section: Time Evolution Of Current Forsupporting

confidence: 53%

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Time evolution of current through insulating paper under DC voltage stress

Bitam-Megherbi

Megherbi

2007

IEEE Trans. Dielect. Electr. Insul.

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The use of paper in electrical insulation, especially in power transformers, remains a topical subject. The interest for the insulating paper, despite the emergence of many synthetic materials is ascribed to its low cost price and its ability to an oil impregnation. However its strong hydrophilic character remains the main difficulty for its implementation in electrical insulation. This affinity to water absorption and/or adsorption shows that a good understanding of the moisture effect becomes imperative. Several studies were carried out on the subject but a systematic study of the moisture effect on overall behavior of paper has not been achieved. This work is meant to be a contribution for this systematic investigation. The first step of this study, which is the object of the present article, concerns an examination of time variation of the electrical currents, under dc stress, for different moisture levels. A particular attention is given to the polarization and depolarization currents. These currents are examined during alternate charges and discharges sequences. An increase of the current, during the application of continuous voltage was noticed. This unexpected phenomenon would be related to an electro-dissociation and/or polarization processes.Index Terms -Paper insulation, dielectric materials, moisture effect, dielectric polarization, electrolytic dissociation, electric field effects.

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Section: Time Evolution Of Current Forsupporting

confidence: 53%

“…The moisture effect on the time variation of this current was studied in our previous works [1]. Dielectric constant and dielectric losses were also studied in a previous work which proved the large effect of the humidity on these two parameters [2].…”

Section: Introductionmentioning

confidence: 95%

Time evolution of current through insulating paper under DC voltage stress

Bitam-Megherbi

Megherbi

2007

IEEE Trans. Dielect. Electr. Insul.

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“…On the other hand, the results presented in Tables 4, 5, and 6 and summarized in Table 7 show clearly that whatever is the moisture level, for a voltage waveform approximately representing a sine wave (THD 0.16%), the definition of tan ı is very easy Downloaded by [University of Windsor] at 00:50 19 November 2014 because the phase difference between sinusoidal signals is clearly defined. In an earlier work, this factor was measured for pressboard containing different rates of humidity [10].…”

Section: Discussion Of Resultsmentioning

confidence: 99%

Experimental Approach of Dielectric Losses Measurement in Insulating Paper under Distorted Voltage Stress

Megherbi

Bitam-Megherbi

Benamrouche

2009

Electric Power Components and Systems

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The present work describes an experimental investigation dealing with the harmonic distortion of the voltage applied to samples of pressboard paper. The investigation especially concerns the study of dielectric losses in order to determine the contribution of each component in these losses. The influence of the moisture level of the samples is also discussed with respect to the influence of the humidity on the insulating system. A new method of determining the losses is proposed; it permits the weighing of the contribution of each harmonic. Three different power supplies with different distortion rates were used in this work. For each experiment, the form and the RMS value of the current and the voltage are reported. The harmonic analysis was carried out, and the results show an important effect of the distortion rate on the voltage and the moisture level on the dielectric losses.

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“…Bitam-Megherbi et al have stated, "among the factors which have a harmful role in electric insulation, moisture remains indisputably the most significant [14]." But the significance has been questioned elsewhere.…”

Section: Ageing Mechanism For Power Cablesmentioning

confidence: 99%

“…This technique has been used extensively in the literature under various circuit configurations to maximize the accuracy of the current measurements [14,18].…”

Section: Measurement Techniques From Previous Researchmentioning

confidence: 99%

Dielectrometry Measurements of Moisture Diffusion and Temperature Dynamics in Oil Impregnated Paper Insulated Electric Power Cables

Thomas

Zahn

2008

Conference Record of the 2008 IEEE International Symposium on Electrical Insulation

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Paper insulated lead covered (PILC) cables have played an important role in underground power distribution for a hundred years. Replacing aged PILC before failure is critical to managing power distribution. Three prominent failure mechanisms accelerate cable aging: temperature stresses, moisture ingress, and partial discharge. The research focuses on the effect of temperature and moisture on the effective (complex) permittivity of the cable insulation. Measurements are performed using cylindrical dielectrometry sensors designed to be wrapped around the cable. The lead sheath of the cable is removed so that the sensors can be placed directly in contact with the insulation. From the measurements, the electrical properties of the material as a function of temperature and transient moisture diffusion are found.A theoretical treatment of the interdigital dielectrometry sensors with a cylindrical geometry is presented. Two classes of the geometry are studied. The φ periodic sensor geometry has electrodes aligned with the cylindrical axis and periodic around the circumference. The z periodic sensor geometry has the electrodes forming rings around the cylinder that are periodic along the cylindrical axis. The material is modeled by concentric rings of homogeneous materials. The electric field solution consists of an infinite summation of Fourier series terms. In finding the field solution and as a consequence of it, the potential, electric field lines, and the impedance between the driving and sensing electrodes are found. A generalized solution to the planar dielectrometry sensor topology is also presented. This solution allows for an arbitrary placement and excitation of electrodes, providing the analytical tools for a new generation of sensors.Dielectrometry sensors for use in φ and z periodic geometries are designed and manufactured on a 4 mil PTFE substrate. An experimental setup is designed and built to provide a temperature and humidity controlled environment for measurements. Special clamping mechanisms are used to secure the sensor to the sample. Custom built hardware is used to excite the sensor at frequencies ranging from 0.005 Hz to 10,000 Hz (over six decades), measure and record the response, and deliver it to a computer for storage and analysis.Steady state measurements are performed at temperatures ranging from room temperature to 100• C. Plastics, woods, and the PILC cable samples are measured. Using the theoretical model, the effective permittivity is estimated from the measurements. An Arrhenius temperature dependence is observed for several materials including the PILC cables. We characterize the temperature dependence of these materials by a master curve and activation energy. Together they give a complete description of the effective permittivity's frequency and temperature dependence.Transient measurements of moisture diffusion are made at constant temperatures for several 4 materials. For some experiments the boundary conditions limit the diffusion of moisture to one direction. When the z...

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The moisture effect on dielectric losses of insulating paper

Cited by 11 publications

References 0 publications

Time evolution of current through insulating paper under DC voltage stress

Time evolution of current through insulating paper under DC voltage stress

Experimental Approach of Dielectric Losses Measurement in Insulating Paper under Distorted Voltage Stress

Dielectrometry Measurements of Moisture Diffusion and Temperature Dynamics in Oil Impregnated Paper Insulated Electric Power Cables

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