Formation of water nanodrops in cellulose impregnated with insulating oil

Żukowski, P.; Kołtunowicz, Tomasz N.; Kierczyński, Konrad; Subocz, J.; Szrot, M.

doi:10.1007/s10570-015-0543-0

Cited by 55 publications

(22 citation statements)

References 8 publications

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“…Similar results have been previously obtained for the DC conductivity in ( _ Zukowski et al 2015a), and for the AC conductivity and the conductivity relaxation time-in ( _ Zukowski et al 2015b). Fig.…”

Section: Introductionsupporting

confidence: 89%

“…0.8 wt% to the level exceeding 5 wt%. As it was mentioned in the paper ( _ Zukowski et al 2015a), water in cellulose gets precipitated in the form of nanoparticles of approx. 2.32 nm that contain approx.…”

Section: Introductionmentioning

confidence: 81%

“…In the papers ( _ Zukowski et al 2014( _ Zukowski et al , 2015a it was found that in a composite of cellulose, mineral oil, and water nanoparticles, the conductivity results from electron tunneling between potential wells formed by nanodrops of water. The well, from which the electron hops, gets positively charged, while the well into which the electron hops obtains the negative charge.…”

Section: Introductionmentioning

confidence: 99%

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Permittivity of a composite of cellulose, mineral oil, and water nanoparticles: theoretical assumptions

et al. 2015

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The paper presents results of testing permittivity of an oil-impregnated electric pressboard containing water nanoparticles depending on AC frequency, moisture content level and the temperature of samples. A new method has been developed for converting experimentally obtained frequency dependences of permittivity determined with the frequencydomain spectroscopy (FDS) to the reference temperature of 293 K (20°C) using exponential dependence of the relaxation time versus temperature. Activation energy of the permittivity relaxation time has been determined for a moist oil-impregnated electric insulation pressboard. It has been established that variations of the moisture content level in a composite of cellulose, mineral oil, and water nanoparticles do not cause any changes in the relaxation time activation energy value, neither in energy states of electrons in potential wells nor in the structure of water nanoparticles. It has been also found that the conversion of experimentally obtained permittivity versus frequency dependences determined with the FDS method to the reference temperature of 293 K (20°C) eliminates temperature dependences that occur in characteristics based directly on measurement results. Once the relative permittivity is converted to the reference temperature it is only its dependence on the moisture content level that remains.

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Section: Introductionsupporting

confidence: 89%

Section: Introductionmentioning

confidence: 81%

Section: Introductionmentioning

confidence: 99%

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Permittivity of a composite of cellulose, mineral oil, and water nanoparticles: theoretical assumptions

et al. 2015

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“…Generally, g can be a function of water molecules' uptake. Another feature is that water in confined systems behaves differently from bulk liquid water; the relative permittivity depends on the average size of volume where water is confined [25,26].…”

Section: Modelling Of Polymer-based Capacitive Humidity Sensorsmentioning

confidence: 99%

Low Humidity Characteristics of Polymer-Based Capacitive Humidity Sensors

Majewski

2017

Metrology and Measurement Systems

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Polymer-based capacitive humidity sensors emerged around 40 years ago; nevertheless, they currently constitute large part of sensors' market within a range of medium (climatic and industrial) humidity 20−80%RH due to their linearity, stability and cost-effectiveness. However, for low humidity values (0−20%RH) that type of sensor exhibits increasingly nonlinear characteristics with decreasing of humidity values. This paper presents the results of some experimental trials of CMOS polymer-based capacitive humidity sensors, as well as of modelling the behaviour of that type of sensor. A logarithmic functional relationship between the relative humidity and the change of sensor output value at low humidity is suggested.

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“…The problem of insulation moisture has been known to the international community for a few decades and it is still a current issue, which is confirmed by the newest publication of the worldwide range: they concern, among others, moisture measurement methods of transformer insulation [6,13,20], also problems connected with forms of water presence [3,13,21] and its migration in the cellulose−electro-insulating liquid system [2,15]. Nowadays, the activities of the international CIGRE Working Group WG D1.52 Moisture measurement in insulating fluids and transformer insulation are in progress.…”

Section: Introductionmentioning

confidence: 97%

Application of capacitive sensor for measuring water content in electro-insulating liquids

Przybyłek

Siodła

2016

EiN

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Article citation info: (*) Tekst artykułu w polskiej wersji językowej dostępny w elektronicznym wydaniu kwartalnika na stronie www.ein.org.pl IntroductionThe presence of water in the electro-insulating system of power devices is a serious operational problem. This problem refers first of all to devices insulated with cellulose materials impregnated with electro-insulating liquids [4,5]. Examples of such devices are power transformers and instrument transformers. This problem also refers to transformer bushing insulators.With passing years of operation of a given device, its insulation moisture rises. This problem has been discussed in different scientific publications many times [2,4,15], mainly in terms of oil-paper insulation moisture of power transformers. Authors of these articles notice that water is not only a decomposition product of cellulose insulation but it also contributes to this decomposition. As a result of water presence in the insulating system and exposure to high temperature, the process of cellulose depolimerization takes place, which results in a decrease of its mechanical strength [1,12,17]. Other disadvantageous consequences of water presence in the insulating system are: electric strength drop of the insulation, lowering the inception voltage of partial discharges [19], and the threat of the bubble effect appearance [8,11], which increases with more moistened cellulose insulation. High insulation moisture forces restrictions of the device load. One of positive aspects of water presence in solid insulation is the increase of its thermal conductivity, which to a certain extent improves cooling of the transformer windings [7]. However, negative results of water presence are predominant and there is a trend to reduce the insulation moisture of power devices as much as possible.Due to long-lasting operation of power devices, the problem of moisture is serious and concerns not only the Polish electric power system but also the systems of most countries. The problem of insulation moisture has been known to the international community for a few decades and it is still a current issue, which is confirmed by the newest publication of the worldwide range: they concern, among others, moisture measurement methods of transformer insulation [6,13,20], also problems connected with forms of water presence [3,13,21] and its migration in the cellulose−electro-insulating liquid system [2,15]. Nowadays, the activities of the international CIGRE Working Group WG D1.52 Moisture measurement in insulating fluids and transformer insulation are in progress. Their purpose is, among others, to improve reliability of water content measurement methods in electro-insulating liquids. Capacitive probe for measuring water content in electro-insulating liquidThe most frequently used method of measuring water content in electro-insulating liquids is titration method which makes use of the Karl Fischer reaction (KFT -Karl Fischer Titration). It is a standardized method [10] which is characterized by high accuracy of water con...

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Formation of water nanodrops in cellulose impregnated with insulating oil

Cited by 55 publications

References 8 publications

Permittivity of a composite of cellulose, mineral oil, and water nanoparticles: theoretical assumptions

Permittivity of a composite of cellulose, mineral oil, and water nanoparticles: theoretical assumptions

Low Humidity Characteristics of Polymer-Based Capacitive Humidity Sensors

Application of capacitive sensor for measuring water content in electro-insulating liquids

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