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Electrical contacts for low voltage circuit breakers

Copper-nickel/graphite composites are potential substitutes for silver based materials used in low voltage circuit breakers. The microstructure versus properties relationships in composties containing a dispersion of graphite particles were thoroughly investigated. New composites have also been prepared using graphite fibres. The electrical conductivity is found to be significantly affect by the graphite volume fraction and by the anisotropy factors of the microstructure while the electrical contact characteristics mainly depend on the graphite fraction adn are stable and sufficient in the graphite range 8 to 12%. The mechanical properties are decreased by the graphite content and the poor interface adhesion between the copper-nickel matrix and graphite.
In order to promote interface adhesion composties were prepared using carbide forming elements (tungsten, silicon, chromium). The chromium content and processing conditions should be tuned in order to promote adhesion without inducing the extensive formation of a brittle phase along the interfaces.
Copper nickel graphite composites when associated with silver carbide yields excellent result for contact resistance and wear.

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Institut National Polytechnique de Grenoble
38402 St Martin d'Heres
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