Non-destructive measuring method to locate inhomogeneities on a contact surface of a vacuum circuit breaker
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Date
2015Type
- Conference Paper
ETH Bibliography
no
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Abstract
One of the most important pre-breakdown phenomena is the field emission
current. It can lead to a warming of a certain area of the cathode and the anode as well.
Emission sites on the cathode’s surface are material inhomogeneities, for example microprotrusions,
which cause microscopic electric field enhancements. Thus electrons are
emitted and accelerated by the field applied between the electrodes. At the cathode surface
these electrons cause a high local current density, which may result in a vaporisation
of a microprotrusion due to joule heating. In addition, the impact of accelerated electrons
at the anode surface causes secondary effects, which may also contribute to a reduction
of the dielectric breakdown strength. To decrease the probability of field emission based
breakdown, microscopic protrusions have to be reduced. This can be achieved by improving
the contact surface. Therefore, a more detailed knowledge of the surface condition
is required. In order to locate microprotrusions it is necessary to open the vacuum bottle
and to analyse the surface with an electron microscope. This is a destructive investigation
and, therefore, practically not applicable. Until now, a non-destructive measurement, which
allows the interior of the vacuum tube to stay intact, has not been introduced. In this contribution,
a non-destructive method will be presented, which allows the location of emission
sites in commercial vacuum tubes by use of time variant external magnetic fields, which
have effect on the internal electron trajectories. Show more
Publication status
publishedEditor
Book title
19th International Symposium on High Voltage Engineering (ISH 2015)Pages / Article No.
Publisher
University of West BohemiaEvent
Organisational unit
03869 - Franck, Christian / Franck, Christian
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