Patent GB-459902-A (GB)
Title: Improvements in or relating to means for controlling the electrical characteristics of direct current generators and transformers
IPC: H02K47/16
Filed: 1935-08-09
Abstract: 459,902. Dynamo-electric machines. PESTARINI, G. M., Societa San Giorgio, Genoa, Italy. Aug. 9, 1935, No. 22578. Convention date, Aug. 16, 1934. [Class 35] Exciting ; rotary transformers.-An electrical power plant comprises a main dynamo - electric machine 1 having excitation arrangements whereby the machine is adapted to supply at variable voltage a continuouscurrent of a magnitude determined by the excitation produced by controlling field winding turns 2 forming part of the excitation arrangements, and an auxiliary machine or machines consisting of two elements 5, 6, connected to the field winding turns 2 to produce ampere turns proportional to the sum of the electromotive forces of the two elements and thus determine the magnitude of the current supplied by the main machine ; the exciter elements 5, 6, are excited by ampere-turns which increase and decrease respectively as the voltage supplied by the main machine increases and the magnetic circuits are magnetically saturated over a large portion of the normal operating range whereby the main machine is given a voltage-current characteristic, Fig. 2, with a substantially flat portion for intermediate values of voltage and drooping relatively for the extreme values of voltage. Exciter 5 has a field winding 7 fed from the main machine and exciter 6 has a separately excited winding 9 and an opposing winding 8 in series with the winding 7. It is explained in the Specification that the speed-torque characteristic of a traction motor should have a shape similar to the characteristic shown in Fig. 2, to give smooth acceleration and regeneration. In Fig. 3, curves a b c and f e d respectively show the voltages of the exciters 5, 6 plotted against the voltage at the terminals of the main machine 1 and the ordinates of the curve g h k m give the resultant electromotive force of the two machines. The same curve may also represent the current traversing the field coil 2, and since the machine 1 is of the type having a series winding 3 opposing the winding 2 and an assisting shunt winding 4, the output current will vary in the same manner as the current in the winding 2. The two elements 5, 6 may be combined into one machine as shown in Fig. 7. In this construction, the rotor is wave wound for four poles and two portions corresponding to two pole pitches cut flux from the magnetic circuit 16, 17, 16 excited by winding 12 and the other two portions cut flux issuing from the magnetic circuit 18, 19, 18 excited by winding 13. Alternatively, as in Fig. 6, the rotor winding may be of any type and the portions within one polar pitch cut the two separate fields. In Fig. 6, the main machine is of the metadyne transformer type and voltages increasing and decreasing respectively with the output voltage are obtained from commutator brushes d, c and d a. The exciter 11 supplies a secondary variator winding 2 the current in which determines the secondary output current. Additional coils creating a constant number of ampere turns may be provided on the exciter, connected across the primary brushes of the main machine, and the windings 12, 13 may be connected to different brushes. In a modification, the exciter 11 feeds the variator winding of a metadyne generator which itself supplies the controlling variator winding of the main machine. A resistance in the output circuit of the exciter may be varied to produce a number of voltageampere characteristics of the main machine. Specifications 399,351, 400,416, [Group XXXVII], 404,734, and 459,858, are referred to.