Solid sate semiconductor suppression of the sparking at the bruskes of DC machines

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Progressive developments in semiconductor design and production methods has led to increased device current and voltage ratings and also a reduction in switching times. It is this latter aspect that has been utilised in an attempt to suppress the sparking that occurs between the trailing edge of a brush and the commutator of direct current machines. The semiconductor device chosen for the investigation was the asymmetric thyristor. The thyristor is used to switch into circuit an auxiliary brush whenever sparking occurs.The auxiliary brush is positioned trailing the main brush and electrically intervening of layer isolated by a small insulation. The auxiliary brush provides a path for the uncommutated current and associated energy to be dissipated in se ries connected resistors. The research has addressed the design of the brushes, brushgear, thyristor triggering and spark energy dissipating resistors. The assessment of sparking has also formed a maj or part of the research. The traditional black band method could not be used since the auxiliary brush obscured the view of the trailing edge of the main brush. The methods tried include: optoelectronic, swivel mirror and a high frequency spark noise detector.