Tracking and surface discharge at the oilߝpressboard interface
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.
Citations
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TL;DR: In this article, the authors present a description of commonly used and modern electrical-based diagnostic techniques along with their interpretation schemes for the condition of the internal cellulosic paper and oil insulation of power transformers.
Abstract: The condition of the internal cellulosic paper and oil insulation are of concern for the performance of power transformers. Over the years, a number of methods have been developed to diagnose and monitor the degradation/aging of the transformer internal insulation system. Some of this degradation/aging can be assessed from electrical responses. Currently there are a variety of electrical-based diagnostic techniques available for insulation condition monitoring of power transformers. In most cases, the electrical signals being monitored are due to mechanical or electric changes caused by physical changes in resistivity, inductance or capacitance, moisture, contamination or aging by-products in the insulation. This paper presents a description of commonly used and modern electrical-based diagnostic techniques along with their interpretation schemes.
72 citations
TL;DR: In this article, the evolutions of creepage discharges were analyzed by correlating the visual records of surface tracking, the phase resolved PD patterns, the discharge current signals and the high speed shadowgraph images.
Abstract: Experimental investigations were carried out to study the tracking process on pressboard in esters under ac voltages. The evolutions of creepage discharges were analyzed by correlating the visual records of surface tracking, the phase resolved PD patterns, the discharge current signals and the high speed shadowgraph images. It is found that the impregnated pressboard is susceptive to discharge erosion occurring on and inside the pressboard, which is characterized by "tree-shaped white and carbonized marks". The gaseous "white mark" channels would attract the subsequent discharges to follow the same routes, and the accumulative energy dissipation in these channels would then result in the carbonization of the channels and the emergence of a "carbonized mark". Once formed, the tree-shaped mark can continue to grow even under a reduced voltage or after a re-impregnation, until it bridges the gap and causes a final flashover. For a mineral-oilimpregnated pressboard, high moisture content (>3.5% by weight) is a necessity to initiate a "white mark"; whereas the "white mark" appears at a lower voltage and develops more easily on a dry ester-impregnated pressboard.
53 citations
TL;DR: The design and manufacturing stages of an ultrasensitive AE sensor optimized for partial discharge detection in power transformers are presented, in detail, and the laboratory tests confirmed that the prototype transducer is characterized by ultrahigh sensitivity ofpartial discharge detection.
Abstract: The acoustic emission (AE) technique is one of the unconventional methods of partial discharges (PD) detection. It plays a particularly important role in oil-filled power transformers diagnostics because it enables the detection and online monitoring of PDs as well as localization of their sources. The performance of this technique highly depends on measurement system configuration but mostly on the type of applied AE sensor. The paper presents, in detail, the design and manufacturing stages of an ultrasensitive AE sensor optimized for partial discharge detection in power transformers. The design assumptions were formulated based on extensive laboratory research, which allowed for the identification of dominant acoustic frequencies emitted by partial discharges in oil–paper insulation. The Krimholtz–Leedom–Matthaei (KLM) model was used to iteratively find optimal material and geometric properties of the main structures of the prototype AE sensor. It has two sensing elements with opposite polarization direction and different heights. The fully differential design allowed to obtain the desired properties of the transducer, i.e., a two-resonant (68 kHz and 90 kHz) and wide (30–100 kHz) frequency response curve, high peak sensitivity (−61.1 dB ref. V/µbar), and low noise. The laboratory tests confirmed that the prototype transducer is characterized by ultrahigh sensitivity of partial discharge detection. Compared to commonly used commercial AE sensors, the average amplitude of PD pulses registered with the prototype sensor was a minimum of 5.2 dB higher, and a maximum of 19.8 dB higher.
49 citations
Cites background from "Tracking and surface discharge at t..."
...At the initial stage of surface discharge development, ther are also 'whit marks' obs rved that indicate a drying out process of the pressboard through moisture evaporation [60,65,66]....
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...At the initial stage of surface discharge development, there are also ‘white marks’ observed that indicate a drying out process of the pressboard through moisture evaporation [60,65,66]....
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...Various terms for surface discharges, such as sliding discharge, creeping discharge, or surface tracking discharge, can be found in the literature [60,61]....
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01 Jan 2012
TL;DR: Partial discharge measurement is a common method for monitoring and diagnostics of power transformers as mentioned in this paper, and can detect insulation malfunctions before they lead to failure and can be used to detect power transformer failures.
Abstract: Partial discharge measurement is a common method for monitoring and diagnostics of power transformers, and can detect insulation malfunctions before they lead to failure. Different parameters extra ...
43 citations
Cites background from "Tracking and surface discharge at t..."
...Surface discharge in oil has been investigated in [14-21]....
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...The results show that the tracking is the result of surface discharge, and that the surface discharge and surface flash-over are two distinct phenomena [14-16]....
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TL;DR: In this paper, the behavior of creeping discharges developing on the pressboard surface was investigated experimentally in palm fatty acid ester oil, natural rapeseed oil and commercial mineral oil under variable ac voltages with 60 Hz, respectively.
Abstract: The behavior of creeping discharges developing on the pressboard surface was investigated experimentally in palm fatty acid ester oil, natural rapeseed oil and commercial mineral oil under variable ac voltages with 60 Hz, respectively. The oilimpregnated pressboard was used as the solid dielectric and it was immersed completely into the same oil. The tungsten needle electrode was installed in the one side of pressboard surface without the counter electrode as a high voltage electrode and a grounded fine copper rod was adhered tightly in the other side of pressboard as a back side electrode. The discharge shape, streamer extension, streamer velocity and tracking at the oil/pressboard interface were observed as a function of the time and voltage by using a still camera equipped with a night viewer. Simultaneously, the discharge current and dissipated energy were measured. The gas components dissolved in oils by the creeping discharge were also examined by the dissolved gas-in-oil analysis (DGA). In this paper, it is presented that there are distinctive events due to the occurrence of creeping discharges.
42 citations
References
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26 Oct 1999
TL;DR: In this article, a functional failure model of power transformer insulation and possible effective methods of the insulation condition assessment are discussed based on practical experience, and a substantial drop in the dielectric safety margin under the impact of moisture, oil by-products, contaminating particles, paper insulation aging and partial discharge activity.
Abstract: Condition-based monitoring of power transformer insulation should center on the prediction of a substantial drop in the dielectric safety margin under the impact of moisture, oil by-products, contaminating particles, paper insulation aging and partial discharge activity. A functional failure model of power transformer insulation and possible effective methods of the insulation condition assessment are discussed based on practical experience.
107 citations
TL;DR: This review describes the development and status of tracking research in Japan and some techniques for improving the tracking resistance of outdoor polymer insulating materials will be discussed.
Abstract: This review describes the development and status of tracking research in Japan. First, the fundamentals of tracking and the influences of environmental stresses on tracking will be treated. Then, the principal tracking test methods currently in use will be characterized. Finally, some techniques for improving the tracking resistance of outdoor polymer insulating materials will be discussed.
83 citations
01 Nov 1986
TL;DR: In this article, the authors present several failures of large power transformers attributed to the static electrification phenomena that have been brought to the attention of Texas Power & Light Company, two of these failures were ours.
Abstract: Since December of 1983, there have been several failures of large power transformers attributed to the static electrification phenomena that have been brought to the attention of Texas Power & Light Company. Two of these failures were ours. Prior to December of 1983, numerical statistics describing failures from static electrification are apparently not readily accessible. IEEE and other reference literature addressed the phenomena, but the magnitude of the problem cannot be quantified in terms of numbers of failures.
74 citations
TL;DR: In this paper, the failure of large power transformers has been attributed to static electrification phenomena since December 1983, and methods for identifying problem units and for reducing static electricity are discussed.
Abstract: Failures of large power transformers which have been attributed to static electrification phenomena since December 1983 are discussed. Methods for identifying problem units and for reducing static electrification are discussed. >
60 citations