Understanding the surface discharge characteristics of thermally aged copper sulphide diffused oil impregnated pressboard material
10 Nov 2015-IEEE Transactions on Dielectrics and Electrical Insulation (IEEE)-Vol. 22, Iss: 5, pp 2513-2521
TL;DR: In this article, the impact of thermal aging with copper sulphide diffused oil impregnated pressboard (OIP) material for surface discharge inception voltage (SDIV) variation was investigated.
Abstract: An attempt has been made to understand the impact of thermal aging with copper sulphide diffused oil impregnated pressboard (OIP) material for surface discharge inception voltage (SDIV) variation. The SDIV of Copper sulphide diffused OIP material reduces with increase in thermal aging. The UHF signals generated due to surface discharges with copper sulphide diffused OIP at the point of inception have frequency content in the range 0.7-1.5 GHz with its dominant frequency at 0.9GHz. HFCT measurement indicated that the rise time of injected current pulse due to surface discharge activity in the negative and positive half cycle of the AC voltage are about 0.8ns and 1ns respectively. It is also found that increase in thermal aging of copper sulphide diffused OIP, the amplitude and width of the current pulse increases. The magnitude of surface charge and its mean life is high with thermal aging temperature of copper sulphide diffused OIP material. Polarity of surface charge acquired by OIP due to AC corona charging depends on the surface condition of the pressboard material and its charge decay rate is lower than under DC voltage. Atomic Absorption Spectroscopy (AAS) and Energy Dispersive Spectrometry (EDS) study confirms the presence of copper sulphide on the surface of OIP and is found to be increased for copper sulfide diffused OIP material compare to unused OIP material. Scanning Electron Microscope (SEM) analysis indicates formation of cracks with thermally aged OIP material. Phase Resolved Partial Discharge (PRPD) study indicates that the surface discharge activity occurs near the peaks of the applied AC voltage at inception and at the rising portion of the applied AC voltage at higher voltages. It is found that the tensile and flexural strength reduces drastically for thermally aged copper sulphide diffused OIP material compare to unused specimen.
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TL;DR: In this article, the authors investigated the effect of sulfur corrosion on the characteristics of transformer cellulosic insulation and showed that sulfur contamination had a minimal effect on the power-frequency breakdown voltage but considerably decreased its long-term electrical life.
Abstract: The life of transformer oil-paper insulation is determined by the insulation property of transformer cellulosic insulation. Existing studies have shown that sulfur corrosion poses a serious threat to the properties of transformer oil-immersed cellulosic insulation due to the reaction of corrosive sulfur dissolved in oil with copper winding. This paper investigated the effect of sulfur corrosion on the characteristics of transformer cellulosic insulation, cellulosic insulation winding samples with different degrees of sulfur corrosion were obtained through an accelerated thermal aging experiment. Then, short-/long-term withstand voltage tests for the cellulosic insulation winding were conducted. Experimental results showed that the contamination of sulfur corrosion had a minimal effect on the power–frequency breakdown voltage of the cellulosic insulation winding but considerably decreased its long-term electrical life. Combined with the analysis of the electrical/physical and chemical parameters of oil-immersed cellulosic insulation, the failure mechanism of transformer oil-immersed cellulosic insulation induced by sulfur corrosion was synthetically discussed and analyzed.
15 citations
TL;DR: It can be concluded that surface charge and trap distribution are helpful to clarify partial discharge (PD) mechanism.
Abstract: Trap plays an important role in the charge transportation of three-layer oil-paper and the investigation of trap parameters at different degradation degree is of great significance for further research of the partial discharge (PD) mechanism. This article considers the turn-to-turn structure of on-board traction transformer. A defect model of three-layer oil-paper insulation was designed for PD test. The PD degradation samples are selected from the inception of PD to the breakdown of PD to study the characteristics of surface potential decay on degradation samples by using isothermal surface potential decay method. Given that, the trap distribution at different degradation stages was calculated and its influence on PD characteristics was investigated. The result shows that AC fluctuation voltages caused by inter-harmonic has a great influence on PD distribution, surface charge distribution and trap distribution. With the increase of degradation, the decay rate of surface potential increases and the decay rate of AC fluctuation voltages is larger than that pure AC. And also, the number of shallow trap with AC fluctuation voltages is larger than that with pure AC. The rate of free charge increases with the number of shallow trap increasing. More free electrons involves in the process of PD, accelerating the aging rate of three-layer oil paper samples. Therefore, it can be concluded that surface charge and trap distribution are helpful to clarify PD mechanism.
6 citations
Cites background from "Understanding the surface discharge..."
...Sarathi and Sahitya Yadav [14] found that the tensile and flexural strength reduces drastically for thermally aged copper sulphide diffused OIP material compare to unused specimen....
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TL;DR: In this paper, the effects of different solid and liquid insulation materials on the surface partial discharge (PD) characteristics were investigated using PD inception voltages (PDIV), apparent charges (pC), and phase-resolved PD (PRPD) patterns.
Abstract: The surface discharge along the interface of solid–liquid insulation is one of the main causes of the deterioration of the life of a power transformer. This experimental study investigates the effects of different solid and liquid insulation materials on the surface partial discharge (PD) characteristics. The liquid insulation materials utilized are mineral oil and synthetic ester, whereas the solid insulation materials are cellulose board and Nomex board. The surface PD characteristics in various combinations of solid and liquid insulation materials are investigated using PD inception voltages (PDIV), apparent charges (pC), and phase-resolved PD (PRPD) patterns, and the comparative analysis is presented. Moreover, topography and composition of samples during surface discharges phenomena have been discussed using high-resolution images and chemical composition obtained using the scanning electron microscope (SEM) and energy dispersive spectroscopy (EDAX). The findings of this article will assist in understanding the behavior of surface PDs under various conditions.
5 citations
TL;DR: In this paper, the surface discharge inception voltage (SDIV) of unaged and copper sulphide diffused OIP material was studied by adopting Ultra High Frequency (UHF) technique.
Abstract: Surface Discharge Inception Voltage (SDIV) of unaged and copper sulphide diffused Oil Impregnated Pressboard (OIP) material was studied by adopting Ultra High Frequency (UHF) technique. Copper sulphide diffusion into OIP material was carried out by thermal aging of pressboard material in Dibenzyl Disulphide (DBDS) added transformer oil. The SDIV reduces with increase of thermal aging temperature. The current pulse injected in positive and negative half cycle during the surface discharge of the AC shows the rise time of 0.8ns and 1ns respectively. The FFT analysis of UHF signal measured during surface discharge process has shown frequency content in the range 0.7–1.2 GHz with its dominant frequency at 0.9 GHz. The life of the charge presented on the pressboard increases with thermal aged specimen. Energy dispersive spectroscopy (EDS) analysis of OIP material indicates presence of copper and sulphur content. Frequency Domain Dielectric Spectroscopy (FDDS) studies indicate the permittivity(er), dissipation factor (tan(δ)), conductivity (σdc) increases and relaxation time (τ), coefficient (α) decrease with OIP material (in air / Nitrogen) aged at higher temperature in DBDS added transformer oil. Cole-Cole double relaxation model was used to understand the dielectric parameters of copper sulphide diffused OIP material. The DC conductivity of pressboard material aged in DBDS included transformer oil follows Arrhenius law and the activation energy decreases with increase in temperature of thermal aging.
4 citations
12 Oct 2021
4 citations
References
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01 Jan 2008
17 citations
"Understanding the surface discharge..." refers background in this paper
...Review of earlier literature indicates that DBDS presence in certain lubricating oil lies in the range 100-1000ppm [17]....
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Proceedings Article•
22 Dec 2009TL;DR: In this article, the authors investigated the thermal dependence of PD activity in new and aged paper insulation, using temperatures up to 145 °C, and provided results of PD monitoring at a range of temperatures with and without bubble formation and discussed these effects on the interpretation of PD levels obtained in either separate source or online PD tests of transformers.
Abstract: Insulation within an oil-impregnated insulation consists of mainly organic materials including mineral oil, cellulose paper and pressboard. Temperature is a major cause of degradation of the cellulose insulation. Increased temperature accelerates chemical change in the insulation thus reducing its lifetime. In addition to normal temperature operation, transformers are sometimes subject to sudden thermal overload and the effect of this on the insulation has not been fully investigated. In particular the partial discharge (PD) activity has not been well documented. This paper investigates the thermal dependence of PD activity in new and aged paper insulation, using temperatures up to 145 °C. At these temperatures there is substantial gas bubble formation and these bubbles have a significant impact on the PD activity. In addition, the level of PD activity is also affected directly by the temperature itself. The paper provides results of PD monitoring at a range of temperatures with and without bubble formation and discusses these effects on the interpretation of PD levels obtained in either separate source or on-line PD tests of transformers. The physical effect of ageing on oil-impregnated insulation is also considered in this paper.
12 citations
"Understanding the surface discharge..." refers background in this paper
..., studied PD activity in OIP material at high temperatures and have concluded that PD activity increases at high temperatures and also the moisture formed due to degradation of cellulosic material have high influence on PD generation at much lower voltages [36]....
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12 Nov 2012
TL;DR: In this article, the authors evaluated the overheating hazard due to zero-sequence flux on tank walls of power transformers, taking into account the influence of the Tertiary Stabilizing Winding (TSW).
Abstract: In this paper the evaluation of the overheating hazard due to zero sequence flux on tank walls of power transformers is presented, taking into account the influence of the Tertiary Stabilizing Winding (TSW). Three-phase three-limb core form transformers are considered in this work, where the component of the zero sequence flux closes its path over the tank wall and cover. This paper complements a previous companion paper where cases of full single-phase load and single phase-to-ground faults are studied with and without delta-connected TSW. Those previously calculated zero sequence currents are here the input sources for computing the zero sequence flux. For that, two methodologies are used. One is based on the Reluctance Network Method (RNM) applying the RNM2D_0 software. The second one is based on the Finite Element Method (FEM). A practical application is presented and both computational methods are compared in order to validate the results.
11 citations
"Understanding the surface discharge..." refers background in this paper
...Another major problem which can cause severe damage to the solid and liquid insulation is the hot spot formation where the local temperature can rise more than 200 oC [11-12]....
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07 Apr 2002
TL;DR: In this article, the behavior of thin PET and PI films (polymers adopted in the above insulation systems) after exposure to the action of surface partial discharges (PD) due to PWM-like voltages was investigated.
Abstract: The adoption, in electrical drives, of power supplies equipped with fast electronic devices lead to new "life" problems (e.g. degradation due to partial discharges) which impact on the design of the relevant electric machines insulation systems. Hereby are reported some results of an investigation about the behaviour of thin PET and PI films (polymers adopted in the above insulation systems) after exposure to the action of surface partial discharges (PD) due to PWM-like voltages. The relevant damage after suitable aging (different humidity (RH%) and different PD exposure times) has been examined through of a procedure based on charge decay measurements on the aged films surface. After corona (both positive and negative) charging the films, the surface charge distribution was obtained at different times, so to get the charge decay profiles. The relevant results, depending on films, ambient PD aging conditions, and corona polarity, showed different degrees of correlation between the films surface degradation, the surface charge distribution and the measured charge decay profiles. The latter profiles analysis suggests that this approach can offer complementary information to investigate the PD degradation phenomena that would impact on the insulation systems performance.
9 citations
TL;DR: In this article, the influence of oxygen and DBPC in by-product formation for diagnosis of open-breathing transformer is elucidated for understanding the mechanism of copper sulfide formation.
Abstract: Copper sulfide deposition on cellulosic insulating materials in oil-immersed transformers is evaluated by heating tests stipulated by IEC 62535. Although this method is suitable for evaluation of the corrosivity of unused insulating oil, the subject remains in diagnosis of the insulating oil used. It is because dibenzyl disulfide (DBDS), which is the prime compounds that cause copper sulfide deposition, is consumed by the reaction with copper during operating of transformer. Therefore, it is necessary to detect the existence of DBDS in insulating oil diagnosed as non-corrosivity by IEC 62535. The proceeding paper [6] reports that Bibenzyl (BiBz) and Dibenzyl sulfide (DBS) will be formed in the insulating oil as by-products of copper sulfide formation between copper and DBDS in oxygen-poor atmosphere which imitated the closed-type transformers. These by-products are considered to be the indication of copper sulfide formation. However, the influence of oxygen and addition agent (e.g. 2,6-di-tert-butylp- cresol) on the mechanism of the by-product formation is unclear. The purpose of this study is to elucidate the influence of oxygen and DBPC in by-products formation for development of diagnosis. It became apparent that benzyl alcohol, benzaldehyde and benzoic acid generate as by-products of copper sulfide formation in the air atmosphere which imitated the open-breathing transformers. Furthermore, it became apparent that the reaction product of benzyl radical and the radical of DBPC generates as by-product of copper sulfide formation in the insulating oil containing DBPC. These by-products are detectable even if DBDS disappears. Therefore, it is thought that diagnosis of the open-breathing transformer is possible by detecting these by-products.
7 citations
"Understanding the surface discharge..." refers background in this paper
...In addition, they have observed that no correlation is observed between amount of copper sulphide formed and benzyl group present in the liquid after ageing, on disappearance of DBDS [21]....
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