The behaviour of a thyristor assisted commutator

Abstract

Development of machines in which sliding contact commutation is assisted by thyristors has led to a need for more knowledge about the behaviour of carbon brushes sliding on slip rings when the current is applied in pulses instead of -.continuously. Of particular interest is the question of relative wear of those parts of the rings that carry current relative to those that do not, the maximum current density at which they can work under pulsed conditions, and the uncertainty of such contacts when a brush is sitting partly on a "conducting" segment and partly on a "non-conducting" segment. To look at the above in a relatively simple way, some rings were rotated and current passed in pulses, of both sine wave and rectangular form. An attempt was made to detect excessive wear or damage on the rings, together with any significant time lag between application of voltage and flow of current. Photographic evidence of the above is presented. To look at the effect of current flow when the contact is uncertain, as is the case when a brush is only partly sitting on a segment, a split ring was used, and current passed to a brush as it passed across the split.