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Advisor(s)
Abstract(s)
Cathode spots on copper–chromium contacts of
vacuum interrupters are simulated by means of a self-consistent
space-resolved numerical model of cathode spots in vacuum
arcs developed on the basis of the COMSOL Multiphysics
software. Attention is focused on spots attached to Cr grains
in the Cu matrix in a wide range of values of the ratio of the
grain radius to the radius of the spot. In the case where this
ratio is close to unity, parameters of spot are strongly different
from those operating on both pure-copper and pure-chromium
cathodes; in particular, the spot is maintained by Joule heat
generation in the cathode body and the net energy flux is directed
from the cathode to the plasma and not the other way round.
An investigation of stability has shown that stationary spots are
stable if current controlled. However, under conditions of high power circuit breakers, where the near-cathode voltage is not
affected by ignition or extinction of separate spots, the spots
are unstable and end up either in explosive-like behavior or in
destruction by thermal conduction. On the other hand, spots live
significantly longer-up to one order of magnitude-if the spot and
grain sizes are close; else, typical spot lifetimes are of the order of
10 µs. This result is very interesting theoretically and may explain
the changes in grain size occurring in the beginning of the lifetime
of contacts of high-power current breakers. A sensitivity study
has shown that variations in different aspects of the simulation
model produce quantitative changes but do not affect the results
qualitatively.
Description
Keywords
Cathode spot Grain size Spot extinction Spot lifetime Stability Vacuum circuit breaker Vacuum interrupter . Faculdade de Ciências Exatas e da Engenharia
Citation
Benilov, M. S., Cunha, M. D., Hartmann, W., Kosse, S., Lawall, A., & Wenzel, N. (2015). Modeling spots on composite copper-chromium contacts of vacuum arcs and their stability. IEEE Transactions on Plasma Science, 43(8), 2253-2260.
Publisher
Institute of Electrical and Electronics Engineers