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Since earlier work (1–4) had shown that polarity effects were important, the present study was designed to measure pressure effects under non-uniform field conditions using each polarity. Part of the study was conducted at high magnification to observe the streamer inception voltage under elevated pressures.
1- The conduction current in oil under AC and positive DC voltages increases in general with increasing field strength or oil temperature. 2- When the oil is subject to positive DC voltage the leakage current is too much smaller than that with AC voltage. 3- The breakdown voltage of oil decreases as the oil quality decreases. 4- The breakdown voltage is lower for positive polarity then for negative...
The progressive improvement in the purification techniques of dielectric liquids renders the measurement of their resistivity more and more difficult, sometimes impossible (especially at room temperature) with conventional AC bridges (SCHERING bridge, transformer ratio bridge) they are not sensitive enough to detect losses (tanδ) or conductance G of a cell of capacitance C filled with a liquid of...
In a negative-needle to plane configuration in transformer oil and liquid nitrogen (LN2), current-voltage (I–V) characteristics and liquid velocities were measured. Well-known linear plots of V vs I1/2 were obtained in the space charge limitation (SCL) for I>10−9 A. The liquid motion in SCL is computed from both the Navier-Stokes equation and the continuity equation by the finite difference method...
Samples of two types of insulating oil used in transformers and switch-gear components in Egypt are experimentally tested to determine the breakdown-change of their dielectric constant and of their breakdown voltage. A standard oil tester is used to apply high voltage to the samples at two different rates and two different time intervals. The breakdown voltage of each sample is measured at the two...
These two new experiments bring us more information about the behaviour of liquid dielectrics. We intend to develop them by studying more liquids and by analysing more precisely the main characters affecting the partial discharges.
An experimental study on the combined γ-radiation and heat effects on the electrical properties of transformer oil is presented. Several samples of fresh unused transformer oil of the type used in Egypt is irradiated in a γ-cell for different time periods, at the same radiation conditions. Each sample, one at a time, is then raised to a different pre-specified temperature. At this temperature, we...
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