FA9EF2C0d01 - 544 IEEE Transactions on Dielectrics and...

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544 IEEE Transactions on Dielectrics and Electrical Insulation Vol. 3 No. 4, August 2996 I. A. Metwally Electrical Engineering Department, Mansoura University, Mansoura, Egypt ABSTRACT The factors affecting corona formation on twin-point/plane gaps are investigated both theoretically and experimentally. In the theoretical analysis, an electrostatic field computation program based on the charge simulation method was used to get, the electric field profile on the plate for different gap lengths and interspacings be- tween the two points. Also, the effect of voltage level, air pressure and gap length on the number of axial streamers occurring across the critical field line was intro- duced for a constant time duration. The variation of the integral of the ionization coefficient with the axial length from the point was studied. Finally, a study of the effect of air pressure and gap length on both the corona inception voltage and criti- cal length was presented. Corona formation in single and twin-point/plane gaps al- so was investigated experimentally under both high direct and alternating voltages. There are many factors affecting such corona formation. The investigated factors were the interspacing between the two points, gap length between the point and the plane, ambient temperature, relative humidity, polarity or frequency of the applied voltage, and electrode material. In order to study and explain such phenomena, a photographic investigation together with a simultaneous measurement of both the applied voltage and the corona current were introduced. Curve fitting of the dc coro- na current vs. gap length and voltage for both single and twin-point/plane gaps gave the conventional relationship, but in case of twin point the power of the gap length varies between 1.2 and 1.3. 1. INTRODUCTION NHV applications there are many locations where two or more adjacent similar electrodes are stressed with the same potential. Consequently, corona on one electrode may modify corona on the other ones 111. Examples of these are the conductor surface conditions due to accumulation of pollutant or scratches during installation of overhead transmission lines. Under these conditions and for long term operation, high local electric field stresses exist which lead to the deterioration of the insulation and disruption of the transmission line conductors by the combined action of the discharge ions bombarding the surface and the ac- tion of chemical compounds that are formed by the discharge [21. Also, a twin-point/plane geometry was used in manufactur- ing the bias probe (known as the boundary probe or Tassick- er’s probe) for measurement of current density and electric field strength [3]. Another important industrial application is in elec- trostatic precipitators, where the negative corona on the dis- charge electrodes forms individual tuft discharges at regular in- tervals along the length of the discharge wires, or at sharp edges and projections on shaped electrodes 141. Each tuft discharge has
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This note was uploaded on 06/08/2011 for the course ELECTRICAL 124 taught by Professor Ghjk during the Spring '11 term at Institute of Technology.

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FA9EF2C0d01 - 544 IEEE Transactions on Dielectrics and...

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