[Prev][Next][Index][Thread]
Positive VS negative streamer
Hi All,
Found the following information. Seems to relate to recent measurements.
Quote:
"EXPERIMENTS CONDUCTED IN THE LABORATORY
To understand the basic mechanism by which the positive corona sheath
is neutralized by the return stroke, we conducted the following experiments
in the laboratory. The potential of the central wire of a coaxial
cylindrical system was raised to a very high level by applying a positive
voltage impulse. This pulse led to the generation of positive space charge
in the space between the cylinders. Photographic observations show that
the generation of space charge was mediated by positive streamers radiating
out from the central conductor (figure 1a). Subsequently, the central wire
was abruptly grounded. This led to a partial neutralization (about 40%) of
the positive space charge. Photographic observations show that this
neutralization was accomplished by negative streamers radiating out from
the central conductor (fig 1b). Most of the negative streamers followed
the same path taken earlier by the positive streamers. However, the
negative streamers could not reach abou!
t one third of the radial distance covered by the positive streamers. This
inability of the negative streamers to reach the edge of the positive space
charge, created by the positive streamers, is probably due to the fact that
the field necessary for streamer propagation is higher for negative
streamers than for positive streamers. As a result, only a fraction of the
space charge could be neutralized by negative streamers. In contrast, a
complete neutralization was achieved in negative polarity, and the positive
streamers were able to travel to the edge of the space charge region
originally created by negative streamers. A detailed description of the
experimental set-up and results were published by Cabrera and Cooray (1992)
(see 2 below)."
In the article he goes on to derive the integral equations to model the
hot corona sheath current, the cold corona sheath current, and the slow
corona current.
(1)A MODEL FOR POSITIVE RETURN STROKES, Vernon cooray, Institute of High
Voltage Research, University of Uppsala, 755 92 Uppsala, Sweden.
1992 INTERNATIONAL AEROSPACE AND GROUND CONFERENCE ON LIGHTNING AND STATIC
ELECTRICITY
Report number: DOT/FAA/CT-92/20
Report date: October 1992
Type of report and period covered: Proceedings, October 6-8, 1992
Document is available to the public through the National Technical
Information Service, Springfield, Virginia 22161
(2)Cabrera, V. and V. Cooray, On the mechanism of space charge generation
and neutralization in a coaxial cylindrical configuration, Accepted for
publication in the Journal of Electrostatics, 1992.