449,924. Dynamo-electric machines. PESTARINI, G. M., Instituto Elettrotechnico Nazionale, Galileo Ferraris, Turin, Italy. March 18, 1935, No. 8433. [Class 35] Excititing; rotary transformers .-A dynamoelectric machine producing continuous-current the value of which is equal to a desired linear function of individual currents of a number of separate continuous-current circuits, has excitation arrangements whereby under any given condition of excitation the output current is maintained at a set value independent of the voltage at the machine terminals, the excitation arrangements including a number of field coils connected respectively with the circuits and together producing a flux determining the value of the output current; the numbers of turns in the excitation coils are proportional to the coefficients connecting the output current with the currents in the several circuits. The invention is particularly applicable to the excitation of a large dynamo-electric machine where it is desired to replace a number of field windings by a single winding, the ampere turns of which are a desired algebraic combination of the ampere turns provided by the individual windings. As shown applied to a metadyne machine 1 having primary brushes a, c connected to a constant voltage source 7, 8 and secondary brushes b, d connected to an output circuit 2, secondary variator windings 4, 5, 6 are connected to the separate determinant circuits. An additional secondary variator winding 3 may be provided to produce at the primary brushes a voltage exactly equal and opposite to that of the source 7, 8. Accordingly, when the windings 4, 5, 6 are de-energized, no current flows in the secondary circuit, but a current in any one of these windings will cause a proportional current flow in the secondary circuit. In a modification, the primary brushes are short-circuited and the coil 3 is connected across the secondary brushes. To ensure more stable operation, the secondary current may traverse a stator winding inducing at the secondary brushes an electromotive force opposing the secondary current. A further winding may be provided in the primary axis inducing between the secondary brushes an electromotive force acting in the same direction as that induced by the primary current flowing between the brushes a, c. By means of this winding, the value of the primary current may be reduced; in an alternative arrangement, the primary current may be reduced by a winding connected in series with the primary circuit and producing flux in the primary axis in the same direction as that produced by the primary current flowing between the brushes a, c. To obtain greater stability, the shortcircuit connection between the primary brushes may include a low resistance stator winding inducing between the primary brushes an electromotive force opposing the primary current. Fig. 5 shows the invention applied to an ordinary dynamo-electric machine 12 having the separate windings 4, 5, 6, a shunt field winding 3 and an opposing series winding 13. The machine is rotated at a speed which would be just sufficient to build up a voltage if the machine were excited by the shunt winding alone. Specifications 404,739, [Group XXXVII], and 417,517 are referred to.