A D-C transformer

The company with which the authors are connected undertook the design and construction of a device using a mechanical commutator which would transform direct current from one voltage to another. The two major commutator problems are current collection and commutation. It is well known that it is difficult to solve these problems especially if certain limits are exceeded. In the case of current collections, the speed of moving contacts cannot be indefinitely increased. In the case of commutation the chief limitation is in the voltage per bar. Accepting this requirement of design, it is necessary to devise circuits which will give very good commutation of current and voltage under all. conditions of service. Such circuits may be arranged to rectify or invert alternating or direct current or to transform direct current from one voltage to another. If rectification or inversion is attempted, two great difficulties are encountered. First, that of obtaining perfect synchronization of the commutator with the alternating potential and, second, the balancing of the current and voltages of the ac system against those of the dc system. These difficulties are absent in the case of transformation of direct current, using two commutators carried on one shaft and connected respectively to the primary and secondary of a suitable transformer. Synchronization is perfect and inherent and if the number of commutator bars per circuit is the same on the primary and secondary sides of the apparatus, a true balance of current and voltage is possible. The work described here was based on this type of apparatus.