A Continuous-Current Generator for High Voltage

Abstract

Of all electro-dynamic machines, the direct-current machine probably is the best understood. It was the first machine to be commercially utilized and it is an interesting matter from an engineering standpoint to follow the evolution which this type of machine has passed through. The first great improvement to be incorporated in this type of machine was the application of commutating poles. As is the case in any radical development, engineering opinion was much divided as to the usefulness of such a construction. At first it was held that commutating poles were only useful where the service was severe, as, for example, in adjustable speed motors covering a large speed range. Today, however, it is well realized that commutating poles are advantageous in all kinds of direct-current machines, except in very small machines of fractional horse power output. It is well understood in the art that commutating poles alone do not offer a perfect solution of the direct-current problem, since there exists in such machines troublesome flux distortions. Many attempts have been made to overcome this by aid of distributed windings, and in this paper is described a form of such windings, which have given excellent results both from an operating and an economical standpoint. This distributed winding consists of two parts, one of which may be considered a counterpart of the armature, and is called a compensating winding. This winding opposes the armature reaction in every point around the circumference and effectively prevents any distortion of the flux. There is also a second winding for supplying the excitation and as is described in the paper, this winding is also distributed. By aid of such field windings, it is possible to meet very extreme conditions of service, for example, as is met with in high-voltage machines. In the machine that is described, the voltage between bars runs up to about 100 volts, or nearly four times the conventional value; nevertheless, the commutation is perfect. Machines rated 15 kw. have been built successfully up to 15,000 volts. One of the mechanical difficulties in building high-voltage, direct-current machines lies in the building of the commutator. A novel type of commutator is described in the paper. This commutator construction provides simple means for holding the segments together, and at the same time secures high insulation qualities.