GB1328781A - Dynamo-electric machines - Google Patents

Abstract

1328781 Improving commutation in dynamoelectric machines NATIONAL RESEARCH DEVELOPMENT CORP 21 Sept 1970 [25 Sept 1969] 47304/69 Heading H2A A dynamoelectric machine comprises an armature having a closed winding around which are distributed connections taken in turn to alternate ones of two commutators 2, 3, each comprising conducting segments 4, mutually spaced apart by amounts equal to the spans of the segments and having a span at least as great as the overall span of a set of brushes 11, 12, or 21, 22 bearing thereon and terminating a respective one of two leads 9 or 10 from a supply terminal 8 which leads include triggered electronic discharge devices e.g. thyristors T 1 , T 2 , and a resistor R serially connected with at least one brush of each set; the commutators and brushes are so positioned that each terminal is always connected to a segment or at least one commutator and as the machine rotates is intermittently connected to segments on both commutators simultaneously to complete circuit paths each embracing the two leads 9, 10 and their thyristors T 1 , T 2 and a part 1 of the winding. The spaces are filled with intersegmental insulation 5, 6 and, in operation, thyristor T 1 is triggered on when leading brush 12 bears wholly on segment 4 and conveys current to the winding, and as the brushes move relative to the commutators the brush 12 contacts segment 1 at which instant thyristor T 2 is triggered on to cause it to pass some of the current to the next winding part and complete the circuit path whereupon a reversal cut-off voltage is applied to thyristor T 1 . At speed this voltage is generated in the part 1 by interpoles, but at low speeds when this voltage is absent the tendencny to sparking is reduced by the resistor R. In modifications wherein each set has three brushes, resistors are connected to two, and the outer brushes may be of carbon fibres and the centre brush of solid carbon. There may be provided in parallel with the two commutators a pair of auxiliary commutators of greater diameter.