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Two kinds of electrodes showing different behaviour with respect to the impurity particles present in a dielectric fluid have been designed and built. Both electrodes have a uniform field region. The first kind is designed in order to avoid as far as possible the attraction of impurity particles into the test volume, whereas the second one is designed to the opposite aim. This is achieved by means...
Polarity and conditioning effects of breakdown in liquid helium and the influence of electrode coating by solid insulator are studied. The breakdown strength under positive needle condition, decreases with repeating breakdown events. However, it increases under negative needle condition, which can be explained in terms of severe damage of cathode surface and it influence on electron emission from...
A study was made of the time-lag characteristics of a trigatron spark gap in a several liquid hydrocarbons for both anode and cathode triggering. The influence of the main gap voltage and of the gap length was investigated. The significance of the results obtained is discussed.
One practical version of an EHD induction pump includes an active travelling wave electrode running along the center of a grounded cylindrical pipe. Laminar flow which takes place in the annulus between pipe and electrode is modelled theoretically in terms of an induced charge layer situated at an arbitrary distance from the center electrode. Calculation of flow rates for various choices of geometry...
Mineral paraffinic oils, now considered for replacement of the dwindling naphthenic oils used in transformers produce solid waxes at low temperatures which can have detrimental effects on the transformer life. Since the electrical and chemical properties of both kinds of oil are almost indentical it is very difficult to determine the presence of paraffins in a sample of transformer oil. Several techniques...
The Coulomb force appears appropriate for laboratory simulations of geophysical flows in spherical geometry. In particular the general atmospheric circulation may be modelled by injecting ions in an insulating liquid between non parallel electrodes (a spherical and a ellipsoidal one) thus generating a meridian flow in the absence of rotation. We study here the flow in the simple geometry of two planes...
An experimental and theoretical study has been made of the induced electroconvection of a dielectric oil in cells with parallel plane and spindle electrodes.
The gas generation in a liquid is studied with a test arrangement simulating an all-film capacitor, a model previously developed. In the case of step voltages, the generation threshold voltage is obtained with good accuracy and low spread by recording bursts on the transient currents. These bursts are associated with the presence of streamers from which result gas generation. The presence of space...
The prebreakdown processes have been recorded in n-hexane, toluene, and Marcol 70, both in a pure state and with selected impurities. The study was carried out using a point-plane geometry. A low ionization potential additive had only a small effect on the breakdown voltage or the streamer propagation speed but did significantly alter the shape of the prebreakdown streamer when the needle was the...
The electrical pre-breakdown current in dielectric liquids under non-uniform field with tungsten tip have been investigated using photo-optical measuing technique and nanosecond rectangular high voltage pulse generator. The streamer propagation velocity is deduced for each dielectrics from the relation curve of gap spacing vs. breakdown time lag. The dependences of the time lag on gap spacing, voltage...
The various mechanisms proposed to explain the conductivity of organic dielectric liquids at high fields (50 to 2000 kV/cm) are considered and their range of validity assessed.
The research work that has been carried out regarding the electrical conductivity of dielectric liquids, under various experimental conditions for industrial purposes or for physical investigations of fundamental character, has not yet been able to explain fully the conduction phenomenon. This is because the problem of conductivity in high fields is quite complicated. Although a considerable amount...
An investigation has been made in order to develop a location technique of corona discharge in insulating oil, on behalf of the development of the UHV transformer. This paper describes the principle of analyzing the corona location by making use of electrostatic probes. The corona produces a space charge in the oil, and induces charges on the probes electrostatically. Thus, the location as well as...
Based on optical studies of pre-breakdown events in negative point-plane gaps, one may distinguish three stages in the liquid breakdown process: (i) the creation of a rapidly expanding vapor cavity adjacent to the point electrode; (ii) the growth of a wave-like disturbance on the surface of the cavity, which we interpret as an electrohydrodynamic instability; and (iii) the runaway growth of the instability...
The results of an experimental investigation of electric induced motion in mineral oil between plane parallel copper electrodes are presented. Instability field and dissipation factor were measured under varying frequency, electrode spacing, temperature and voltage-stress conditions. The motions were observed by means of laser schlieren. It is shown that the field is in good agreement with theoretical...
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