Arrangement for preventing chattering and scoring of direct-current slip-ring brushes

Claim 2

Arrangement for preventing chattering and scoring of the direct-current, slip-ring brushes of a synchronous machine having an excitation winding and slip-rings connected to the winding for receiving direct-current excitation through the brushes, the brushes being operated for given periods of time with minimal and zero values of the excitation current, the arrangement comprising two rectifying means for supplying the slip rings with directcurrent through the brushes, the brushes being grouped into two brush sets, each of said sets including at least two brushes corresponding to respective ones of the slip rings, the brushes of each set being connected to a corresponding one of said rectifying means, and circuit means for short circuiting the brushes of one of said sets together so as to cause the brushes of the other one of said sets to be supplied with direct-current during said periods of time, said last-mentioned current bypassing the excitation winding of the synchronous machine and being of sufficient magnitude to prevent chattering and scoring of the brushes.

Claim 3

The arrangement of claim 1 wherein each of said rectifying means has an alternating-current input end and wherein the arrangement comprises alternating-current supply means connected to said input end of each of said rectifying means, and each of said rectifying means comprising control means for adjusting the direct-current supplied to the slip rings.

Claim 4

The arrangement of claim 2, said alternating-current supply means comprising an alternating-current constant voltage generator.

Claim 5

The arrangement of claim 3 comprising coupling means for coupling said voltage generator to the synchronous machine.

Claim 6

The arrangement of claim 2, each of said rectifying means comprising a plurality of rectifying branches connected in parallel across the brushes of the corresponding brush set, each of said branches comprising two controllable rectifying components connected in series in the same rectifying direction, the circuit connection serially connecting the components of each branch defining a terminal of said input end, and said circuit means comprising two controllable rectifying components serially connected together at a center node to form an additional rectifying branch, said additional rectifying branch being connected antiparallel across one of said rectifying means, said center node being connected to the terminal of one of said branches of said one of said rectifying means, each of said rectifying components of said additional rectifying branch having control means for controlling the flow of current therethrough, whereby said one rectifying means is blocked when said control means of said components of said additional rectifying branch is released to place said additional rectifyIng branch in conduction thereby placing a short-circuit current path across the brushes of said brush set corresponding to said one rectifying means during said periods of time.

Claim 7

The arrangement of claim 5, said components of said additional rectifying branch being thyristors.

Claim 8

The arrangement of claim 6, said control means of the other one of said rectifying means comprising gate electrodes corresponding to respective ones of said rectifying components thereof, said gate electrodes being connectable to an adjustable voltage for controlling the current passed through the brushes of said brush sets and the slip rings during said periods of time.

Claim 9

The arrangement of claim 5, said alternating current supply means comprising an alternating-current constant voltage generator, a switch, a transformer connectable to a source of alternating-current energy through said switch, a summing transformer assembly for exciting said generator, said transformer assembly being connected to said transformer, said transformer being connected so as to apply a determined voltage to said transformer assembly when said switch is closed, said determined voltage applied to said transformer assembly in turn causing said generator to apply a voltage to the other one of said two rectifying means whereby said control means of said other rectifying means is released and the current supplied by said generator is of sufficient magnitude to prevent chattering and scoring of the brushes.

Claim 10

The arrangement of claim 5, said alternating current supply means comprising an alternating-current constant voltage generator, a rectifier assembly forming part of the generator for providing direct-current excitation to the excitation winding of the generator, said generator including controllable parallel path means connected to said rectifier assembly for adjusting the excitation current supplied by said rectifier assembly to said excitation winding of said generator so as to cause said generator to supply a current to said other one of said rectifying means sufficient to prevent chattering and scoring of the brushes.

Claim 11

The arrangement of claims 2, said circuit means comprising an auxiliary rectifier connected in parallel with one of said rectifying means, and a switch connected across the brushes of the brush set corresponding to the other one of said rectifying means, said switch being closable to short circuit said last-mentioned brushes, said auxiliary rectifier being connectable to a voltage that causes said auxiliary rectifier to supply the brushes and slip rings with a current when said switch is closed and when both of said rectifying means are blocked, said last-mentioned current being of sufficient magnitude to prevent chattering and scoring of the brushes during said periods of time.