Characteristics of corona discharge and spark breakdown in nonuniform field and uniform field gaps in SF6 gas

1986 ◽  
Vol 106 (4) ◽  
pp. 37-46 ◽  
Author(s):  
Akira Watanabe ◽  
Tatsuzo Hosokawa ◽  
Yasunori Miyoshi
Keyword(s):  
Corona Discharge ◽  
Nonuniform Field ◽  
Uniform Field ◽  
Spark Breakdown

The mechanism of spark breakdown in nitrogen, oxygen and sulphur hexafluoride

1972 ◽  
Vol 329 (1577) ◽  
pp. 171-191 ◽  
Keyword(s):  
Space Charge ◽  
Arc Discharge ◽  
Time Lag ◽  
Image Intensifier ◽  
Uniform Field ◽  
Sulphur Hexafluoride ◽  
Breakdown Mechanism ◽  
Formative Time ◽  
Free Region ◽  
Spark Breakdown

An image converter and a 4-stage image intensifier have been used to investigate the development of spark breakdown in a 3-cm, uniform-field, gas-discharge gap. The growth of ionization, initiated by a burst of electrons a t the cathode, has been observed for overvoltages up to 25 % in nitrogen, oxygen and sulphur hexafluoride a t pressures in the range 13 to 40kPa (100 to 300 Torr). In nitrogen, time resolved shutter and streak records have been obtained which demonstrate, that, at low overvoltages, breakdown is preceded by the formation of a diffuse glow discharge whereas, at voltages well in excess of the static breakdown voltage, the arc discharge is formed directly in the track of the initial electron avalanche, as a result of space-charge distortion of the applied electric field. This change with overvoltage has previously been ascribed to a transition from a Townsend to a streamer breakdown mechanism; the present results, however, do not entirely support this view. In oxygen and sulphur hexafluoride, no such change in the form of ionization development has been observed and it is concluded from the evidence obtained that, even a t very small overvoltages, the development of ionization is strongly affected by space-charge distortion of the applied field. Photographs obtained in sulphur hexafluoride have been correlated with measured formative-time-lag data showing the time-lag-free region reported previously by Kuffel. Some conclusions have been drawn regarding the breakdown mechanism under these conditions.

Measurements of Corona Discharge in Non-Uniform Field Freon GAP

2014 ◽  
Vol 7 (4) ◽  
pp. 47-61
Author(s):  
A. S. Hasaani ◽  
Hassan J. Mohammed
Keyword(s):  
Corona Discharge ◽  
Pressure Range ◽  
Outer Diameter ◽  
Uniform Field ◽  
Design Considerations ◽  
Wide Range ◽  
Onset Voltage ◽  
Inner Diameter ◽  
Gap Spacing ◽  
High Degree

Corona Discharge have been recorded in pin-to pin electrode at gas pressure gaps with high degree of non-uniformity electric field. For a wide range of experimental applicability the pin to pin electrode was used over pressure range from 1bar to 3bar and gap spacing from 0 to 5mm.High –pressure dc corona discharge experiments have been carried out in a 16cm long glass chamber with an inner diameter and outer diameter are 16.8cm, and 19cm respectively. Corona onset voltage and breakdown voltages were reached. The design considerations of the setup allow to use pin to pin electrode type geometries. Electronegative gases such as air, Freon (R22), were separately used for low temperature corona generation. The experiments have been carried out under ambient Laboratory conditions of temperature (19-24 oC), and humidity. The present experiment were studies the relation between the (V-P) and (V-d), on other hand, we study the relation between the current and applied voltage.

scholarly journals Measurements of Corona Discharge in Sharp –to-Plane Electrodes Configuration

2018 ◽  
Vol 11 (3) ◽  
pp. 79-84
Author(s):  
Hassan J. Mohammed
Keyword(s):  
Electric Field ◽  
Corona Discharge ◽  
Breakdown Voltage ◽  
Physical Process ◽  
Applied Voltage ◽  
Threshold Value ◽  
Precise Knowledge ◽  
Dc Current ◽  
High Degree ◽  
Spark Breakdown

A Dc positive sharp- to –plane Corona phenomena  have been studied in electronegative gases (air ,and SF6 ) for pressure up to (3.2bar and gap length from 0.1 to 0.5 cm), with high degree of non-uniformity electric field. The corona –breakdown phases can exhibit anomalous characteristics. The exact physical process of such phenomena is not yet fully understood complete. To better understand this process precise knowledge about corona and spark discharge is necessary. Hence the dependency of corona inception and spark breakdown voltage on the pressure, non-uniformity field factor  and the type of applied voltage ,also the type of materials. The steady  region of corona discharge is observed in the ( sharp- to- plane ), for applied voltage between the threshold value voltage and onset value , we observe an effect that attaching gases. A Townsend type of discharge develops in the region close to point. At voltages above the onset value , the burst pulses are replaced by a Dc current ,and in some cases 'pre-breakdown ' streamer are also observed.

A High Performance Energy Analyzer for Use in Electron Scanning Microscopy

1969 ◽  
Vol 27 ◽  
pp. 14-15
Author(s):  
A. V. Crewe ◽  
M. Isaacson ◽  
D. Johnson
Keyword(s):  
High Performance ◽  
Vertical Plane ◽  
Median Plane ◽  
Electron Gun ◽  
Uniform Field ◽  
Loss Mechanism ◽  
Electron Scanning Microscopy ◽  
Sector Type ◽  
Double Focusing ◽  
Electron Energy Loss

A double focusing magnetic spectrometer has been constructed for use with a field emission electron gun scanning microscope in order to study the electron energy loss mechanism in thin specimens. It is of the uniform field sector type with curved pole pieces. The shape of the pole pieces is determined by requiring that all particles be focused to a point at the image slit (point 1). The resultant shape gives perfect focusing in the median plane (Fig. 1) and first order focusing in the vertical plane (Fig. 2).

Resolution in photoelectron microscopy

1991 ◽  
Vol 49 ◽  
pp. 458-459
Author(s):  
G. F. Rempfer
Keyword(s):  
Electron Microscopy ◽  
Electric Field ◽  
Ultraviolet Light ◽  
Uniform Field ◽  
Virtual Image ◽  
Lens System ◽  
Photoemission Electron Microscopy ◽  
Planar Electrode ◽  
Electron Lens ◽  
Photoemission Electron

In photoelectron microscopy (PEM), also called photoemission electron microscopy (PEEM), the image is formed by electrons which have been liberated from the specimen by ultraviolet light. The electrons are accelerated by an electric field before being imaged by an electron lens system. The specimen is supported on a planar electrode (or the electrode itself may be the specimen), and the accelerating field is applied between the specimen, which serves as the cathode, and an anode. The accelerating field is essentially uniform except for microfields near the surface of the specimen and a diverging field near the anode aperture. The uniform field forms a virtual image of the specimen (virtual specimen) at unit lateral magnification, approximately twice as far from the anode as is the specimen. The diverging field at the anode aperture in turn forms a virtual image of the virtual specimen at magnification 2/3, at a distance from the anode of 4/3 the specimen distance. This demagnified virtual image is the object for the objective stage of the lens system.

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