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Laser-excited fluorescent (LEF) probes are being investigated as a means of detecting low level electrical damage in insulators. These dyes selectively fluoresce at certain damage sites, showing the location and nature of the damage. The fluorescence characteristics differ for each dye, making it possible to focus on specific kinds of damage by judicious choice of dyes. This technique is sensitive...
We made extensive studies on treeing phenomena of polyethylene. The treeing resistance at 77 K is much higher than that at room temperature [1]. We also reported that the ac tree starting voltage at room temperature is drastically increased by degassing of sample; the removal of oxygen absorbed in polymer suppresses the tree channel growth [2].
The reduction of loss tangents of oil-impregnated capacitors is very important in order to prevent dielectric heating that may lead capacitors to thermal breakdown. Here, the authors report that loss tangents of capacitors are remarkably reduced when organosilane compounds are added to oil.
In solid organic dielectrics subjected to high and non-uniform electric stress gradients, failure usually occurs by a mechanism called treeing. The type of damage which progresses through the dielectric under electric stress in dry environment is called electrical treeing. In extruded dielectrics, failures, which do not occur promptly but rather appear to be the result of an aging process, are most...
Space charge may lower the breakdown strength of solid insulation by making local electric fields bigger than the applied field. One extensive study[1] of this phenomenon led to a proposal to blend crosslinked polyethylene (XLPE) insulation with an ionomer to reduce space charge build-up. The authors used contact electrification (no applied field) as a measure of the tendency for a polymer to charge...
Kerr electro-optic field and charge mapping measurements in electron beam irradiated polymethylmethacrylate (PMMA) in air have shown interesting two-dimensional fringing field effects near the sample edges [1–3]. This is because positive ions in the air, ionized by the electron beam, are attracted to the electrons trapped in the sample. This attraction forms a zero potential surface with zero electric...
In high resistivity oil, the electric field distribution is well described by a model based on charge carrier generation through the dissociation of a species of ion pairs in the liquid bulk. As liquid conductivity increases, the close agreement between model and experimental results weakens. The aim of this work was to determine whether or not there exists a violation of the model assumption that...
Polyvinylidenefluoride (PVDF) is attracting considerable scientific and practical interest because of its electrical properties [1]: The material assumes piezoelectric and pyroelectric behavior after suitable poling. Several poling techniques have been used, including the thermal, corona, high-field, and, very recently, the electron-beam methods [1–3].
Several attempts have been made to understand and anticipate the failure of insulation by partial discharges [1–4]. A large scatter is observed in relation to quantities characterising, partial discharges [PD]. Failure by PD, very often, does not take place where either the stress or the pulse magnitude or both are a maximum [1]. The total discharge magnitudes summed upto failure time [Qtp] are associated...
One of the major causes of failure of polypropylene (PP) film high voltage capacitors is PD (partial discharges). PD occurs in the air gaps in the inter layer spaces present due to variation in tightness of windings. It is also possible that the air gaps present may be at different sub-atmospheric pressures due to vacuum impregnation. Therefore it becomes essential to undertake PD studies at pressures...
Since a long time the existence of Partial discharges (PD) in transformer oil was doubted because breakdown and inception levels are very close. This confirms the presently accepted fact that [1] PD occur in oil. In the breakdown process the formation of a “bubble” or “cavity” is accepted generally as a part of the initiatory process. When the bubble reaches a “critical size” a discharge occurs [2]...
Treeing is a complex ageing process leading to electrical breakdown under electrical stress. It depends on the ambient conditions whether electrical, water or electro-chemical trees are formed. Experience shows that trees are not initiated or propogated in a foreseeable manner. Trapped charges seem to play an important role.
Electronic energy transfer from the first and higher states of excited naphthalene molecules to biacetyl molecules was observed from 560-nm photosensitized biacetyl emission.
A detailed description of our revised method of preparing PE and XLPE samples to be used for the investigation of the fundamental parameters of these two materials will be presented. The latest findings regarding the long term conductivity of the specimens under high and constant electrical field, when temperature was varied in a cycling (24h) manner from room temperature (40° C) to about the maximum...
Graded insulation methods (e.g. permittivity grading) have been already known for improving the dielectric strength of power cables.1)2) The reduction of the voltage resistance of a plastic insulated solid cable usually occurs due to defects which might be formed within interfaces of the extruded layers. One method to prevent the influence of defects on breakdown voltage is to enrich the conductor...
In recent years the powerful new techniques of time domain dielectric spectroscopy (TDDS) have revolutionized the field of high frequency dielectric measurements. However, due to the relative newness of the method many questions remain unresolved concerning the applicability of TDDS and the interpretations and limitations of the measurements. In previous and continuing work we have attempted to use...
Technical advances and reductions in cost of computer hardware and software have reached the point where personal computers can mimic the behavior of experts in assisting in both the performance of complex testing procedures, and in diagnosing the significance of the results. The computer program described here acts as an expert assisting in the performance and diagnosis of the results of discharge...
Partial discharges in voids are traditionally discussed in terms of an equivalent capacitive network, the abc-model [1,2]. A void is represented by a capacitance, and discharges within the void are simulated as a partial or a complete discharge of this capacitance. This simple approach has been so successful with respect to measurement techniques that there is a tendency to identify the equivalent...
This paper reports on the progress of a research project intended to develop a method and instrumentation to detect, locate and characterize partial discharges and faults in the insulation of underground cable circuits. The method is non-destructive and applicable in-situ. It is designed to overcome the adverse effects of high ambient noise and high signal attenuation due to lossy semiconducting shields...
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