Abstract
An experimental apparatus was constructed to study the contact of electrical brushes passing high currents. This apparatus consists of a 100 mm copper slip ring and a brush holder which can be loaded against it. The surface temperature of the brush, the extent of contact and the friction can be measured with this apparatus. Four brush materials were studied: one electrographitic brush and three silver-filled graphite brushes. The results of the experiments showed that above a particular threshold speed the brushes exhibited a sparking phenomenon which consisted of periodic motion of a cluster of small sparks on the brush surface. The peak temperature and the periodicity of the sparking were shown to be a function of the properties of the brush material. A theoretical model of the sparking phenomenon has been developed which shows good agreement with the sparking motion observed using the electrographitic brush.
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