C OMPANION papers present some of the inherent possibilities and the useful applications for dynamoelectric amplifiers. 1 ' 2 They have also clearly pointed out that the inherent value of such an amplifier is determined by three characteristics: (1) ratio of response or sensitivity; (2) speed of response; and (3) stability. This paper describes the essential de sign features of two-stage dynamoelectric amplifiers, known as "amplidyne" genera tors, which enable satisfactory values for these three characteristics to be ob tained. Typical performance curves and oscillograms are shown, indicating the Paper 40-10, recommended by the AIEE committee on industrial power applications, and presented at the AIEE winter convention, New York, Ν. Y., January 22-26, 1940. Alec Fisher is designing engineer, General Elec tric Company, Lynn, Mass. Ξ. For all numbered references, see list at end of paper. type of performance that has been found satisfactory in service. Preliminary Analysis The amplidyne generator is funda mentally an armature-excited machine, in that the armature is essentially the source of main excitation, and it is also the source of main power output. The first stage of amplification is from the control field to the short-circuit axis and the second stage from the short-circuit axis to the power-output axis. The total amplification is equal to the product of first and second stage amplification. Figures la and lb show a two-pole d-c armature with two pairs of brushes in quadrature. In order to simplify the figure, the frame is not shown and the assumption is made that the brushes have ideal commutation characteristics. Loca tion of windings is shown for the pure amplidyne generator with (figure lb) and without (figure la) a quadrature cycles per second. This is likely to be a frequency which is representative of the control function for which the system is to be used, and it has been found that in such cases the electromechanical reso nance is apt to be a very real problem, which must be foreseen in the design. In such cases it is found to be desirable to make the inductance of both generator and motor as low as possible by distrib uted compensating windings at the same time as the mechanical inertia is kept as low as possible. Both these factors tend to place the electromechanical resonance frequency above the frequency of the control functions, thus avoiding any tendency to mechanical oscillations. When a control system is desired which demands a still higher ratio of amplifica tion than is attainable ma single dynamo electric amplifier it is possible to intro duce a first stage of electron tubes of the type used in radio sets. Such tubes are adapted to an output sufficient to control an amplidyne whereas the primary con trol energy of such tubes is measured in microwatts. We have thus established 1940, VOL. 59 simple means for industrial purposes to amplify a minute energy such as a beam of light into a quick and accurate control of power flow of many horsepowers. It is hoped that this will open up many new ...
