Influence of ambient medium on thermal ageing of pressboard in transformer oil containing dibenzyl bisulphide (DBDS)
01 Oct 2017-IEEE Transactions on Dielectrics and Electrical Insulation-Vol. 24, Iss: 5, pp 2836-2846
TL;DR: In this article, the impact of thermal ageing of pressboard material in transformer oil containing dibenzyl disulphide (DBDS) under different ambience, such as air, N2, He and vacuum has been studied to understand the level of copper sulphide diffusion.
Abstract: Impact of thermal ageing of pressboard material in transformer oil containing dibenzyl disulphide (DBDS) under different ambience, such as air, N2, He and vacuum has been studied to understand the level of copper sulphide diffusion. The characteristic variations in electrical and thermal properties of copper sulphide diffused oil impregnated pressboard (OIP) material have been measured under different ageing conditions. Surface charge accumulation studies with AC and ±DC voltages showed that surface charge decay time was longer in air aged OIP material. Surface discharge studies by adopting ultra-high frequency (UHF) sensing indicated a reduction in the SDIV with the level of ageing although the characteristic variation in flashover voltage (FOV) under lightning impulse (LI) voltage is almost the same. Also the SDIV reduced with increase in frequency of supply voltage. Thermo-gravimetric analysis (TGA) indicated that maximum weight loss temperature (Tmax) of the cellulose constituent of OIP material decreased with ageing. Laser induced breakdown spectroscopy (LIBS) was adopted to quantify the diffused copper sulphide contaminant in OIP material and the results were compared with the inductively coupled plasma (ICP) spectroscopy based analysis. Based on these studies, deteriorating effect of ageing medium on several properties of OIP material was understood.
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TL;DR: Results indicate that oil-paper insulation is prone to trigger flashover at higher temperatures, because thermal excitation helps more carriers to escape from deep traps and participate in the process of flashover.
Abstract: Oil-paper insulation will inevitably endure impulse voltage with a superimposed dc voltage (superimposed voltage) because of introduced lightning or switching, which can induce charge accumulation and trigger flashover during the operation of a converter transformer. Temperature rise is also a nonnegligible factor that can significantly influence the performances of oil-paper insulation. This paper aims to reveal the effects of ambient temperature and superimposed voltage on surface charge and flashover behaviors in an oil-paper insulation system. Surface potential decay (SPD) experiments were performed under superimposed voltage with various polarity and amplitude combinations and at the temperature ranging from 20 °C to 80 °C. The results show that the initial surface potential and decay rate increase as the amplitude of the impulse voltage increases at 20 °C. The initial surface potential declines, and the process of SPD is accelerated at higher temperatures because of the increased concentration of shallow traps. Subsequently, flashover tests were conducted under superimposed voltage. It is found that flashover occurs after applying superimposed voltages even with a rather low dc voltage. In addition, the dc voltage component is primarily responsible for flashover. Weibull results also indicate that it is prone to trigger flashover at higher temperatures, because thermal excitation helps more carriers to escape from deep traps and participate in the process of flashover. Accordingly, the insulation characteristics of oil-paper system can be significantly influenced by superimposed voltage and temperature, which should draw great concern among the power grid.
10 citations
Cites background from "Influence of ambient medium on ther..."
...In addition, temperature rise in a converter transformer will cause the degradation of the electrical performance of the oil-paper insulation [6]....
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7 citations
TL;DR: In this paper, the authors reveal the influence of ambient temperature on surface charge and discharge behaviors under DC voltage and show that more carriers escape from deep traps to participate in the procedure of surface discharge at higher temperature, which declines the surface discharge voltage.
Abstract: Ambient temperature has significant influence on properties of oil–paper insulation, which makes surface discharge process complex. This paper aims at revealing the influence mechanism of ambient temperature on surface charge and discharge behaviours under DC voltage. The oil–paper with thickness of 0.08 mm was used and the ambient temperature varies from 20 to 80°C in this paper. The results of surface potential decay (SPD) experiments show that the initial surface potential declines and the process of SPD is accelerated with increasing temperature because of higher carrier mobility. Additionally, both shallow and deep trap energy level become deeper, the shallow trap density is enlarged while the deep trap density is shrunken at higher temperature. The surface discharge tests were performed and Weibull results indicate that it is prone to occurring surface discharge at higher ambient temperature. The possibility of surface discharge under negative voltage is larger than that under positive voltage because of polarity effect. It is concluded that more carriers escape from deep traps to participate in the procedure of surface discharge at higher temperature, which declines the surface discharge voltage.
7 citations
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TL;DR: The goal is to show how much space charge can contribute directly or indirectly, through local electric field magnification or alteration, to increase ageing rate or even trigger more energetic, thus faster, degradation processes in insulation design and electrical apparatus long-term performance/reliability.
Abstract: Considering the title of this paper, one might think that everything has been said, shown, proven and discussed already on ageing and failure of electrical insulating materials, based on at least half century of research work and field feedbacks. However, perhaps there is still room to collect ideas and speculate on apparently proven or brand new concepts, such as the interrelation between ageing mechanisms and physically measurable quantities such as space charge, partial discharges and conduction current. The latter is, indeed, the scope of this paper, which is taken from the Whitehead Memorial Lecture given at the 2010 IEEE Conference on Electrical Insulation and Dielectric Phenomena (CEIDP). On one hand we will revisit the concepts of space charge accumulation in insulating (polymeric) materials, considering also the latest achievements which deal with ultra-fast charge pulses (solitons), on the other hand we will discuss how space charge can contribute to ageing rate under dc, ac or impulsive voltage, directly through electric field alteration, or indirectly modifying a fundamental ageing factor such as partial discharges.The goal is, at the very end, to show how much such basic investigations can have a fundamental impact on insulation design and electrical apparatus long-term performance/ reliability.
234 citations
Additional excerpts
...enhancing the local electric field [22, 23]....
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TL;DR: In this paper, it is argued that hydride formation by the primary ions and possibly charge exchange reaction with water molecules followed by proton transfer reactions are the mechanisms by which these clusters are produced.
Abstract: Mass‐spectrometric studies of the ionic species formed in corona discharges in nitrogen, oxygen, and air have been carried out at water concentrations from 1.7×10−2 to 0.65 mole % and total pressures up to one atmosphere. The importance of water in this system has been demonstrated by the dominant presence of (H2O)nH+ ion clusters at water concentrations as low as 4.1×10−2 mole %. Evidence is presented for the formation (HO2)+ and (N2H)+ ions as possible intermediates in the formation of these clusters. It is argued that hydride formation by the primary ions and possibly charge‐exchange reaction with water molecules followed by proton‐transfer reactions are the mechanisms by which these clusters are produced. Simple hydration of other ionic species of the discharge, e.g., O2+(H2O)n, NO+(H2O)n, and (NO2+) (H2O)n, at water concentrations below 5.5×10−2 mole % have also been observed.
228 citations
"Influence of ambient medium on ther..." refers background in this paper
...Positive or negative ions are involved in transferring the charge from the corona needle to the sample surface [29, 30] depending on the positive or negative polarity of charging voltage, respectively....
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09 Mar 2006
TL;DR: In this article, the relationship between radiated ultra-high frequency (UHF) signals and electric charge in a partial discharge (PD) current pulse for PD sources in oil insulation was explored.
Abstract: Investigations are reported into a range of defects causing partial discharge (PD) activity in high-voltage oil-insulated equipment. The aim is to explore the relationship between radiated ultra-high frequency (UHF) signals and electric charge in a PD current pulse for PD sources in oil insulation. Experiments are performed under high-voltage AC conditions using electrode configurations that included a sharp protrusion, a bad contact, and a free metallic particle. A broadband current transformer is used to measure the PD current pulses with the UHF signals being detected using a pair of sensors mounted inside a metal tank surrounding the PD sources. Current pulses and UHF signals were recorded simultaneously using an oscilloscope with a bandwidth of 3 GHz. The level of correlation between the energy of the radiated UHF signals and the charge content of PD pulses is shown to vary depending on the defect type. Polarity-dependent UHF spectral content and ratio of UHF signal energies measured at the two sensors are shown to exhibit characteristics dependent on the discharge behaviour. These results and the analysis procedures introduced will contribute to the development of effective UHF monitoring systems for oil-insulated high-voltage plant.
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TL;DR: In this paper, the nature and causes of corrosive sulfur induced failures in oil-filled transformers and shunt reactors are examined in the presence of paper tapes insulating the conductors.
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105 citations
"Influence of ambient medium on ther..." refers background in this paper
...The deposition of copper sulphide on the windings and insulation material has been observed in a failed transformer which had affected the insulation performance of transformers [6-9]....
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TL;DR: A different approach to the study of surface tracking reveals a new view of the oil-pressboard interface and suggests a link between the electric double layer and the boundary layer as discussed by the authors.
Abstract: A different approach to the study of surface tracking reveals a new view of the oil-pressboard interface and suggests a link between the electric double layer and the boundary layer.
100 citations