The Amplidyne (General Electric Company)

Author: E.E. Kimberly

The shunt-field circuit of the generator in the Ward-Leonard system of Fig. 29-7 is highly inductive, and so the current in it changes slowly after the field-rheostat setting is changed. For this reason the voltage change at the generator terminals is sluggish and not satisfactorily responsive for some purposes. The amplidyne generator, shown in Fig. 29-8, has a very rapid response to changes in exciting voltage, and permits the accurate control of great power by small changes in little power.

Fig. 29-8. Amplidyne Generator

In Fig. 29-8 the exciting or control field flux ϕe is produced by a few ampere-turns only in the small exciting-field coil. The armature, driven at constant speed in this field flux ϕe, generates voltages in the usual manner about the vertical axis. Brushes BI and B₂ on this axis are short-circuited and so permit currents to flow in all armature conductors. These currents produce the usual armature reaction field ϕa, which is vertical in the figure and across the excitation field ϕe. The armature rotation in the field ϕaj which its own currents have produced, generates a new set of voltages around the horizontal axis. Brushes B₃ and B4 on the horizontal axis make these voltages available at the load terminals. The load currents and the short-circuit currents obviously cannot exist simultaneously in the armature conductors, but combine algebraically to produce the true current. The excitation power is extremely small compared to the full-load output watts, and so may be supplied by a small electronic control circuit. The response in generator voltage change is very rapid and is especially useful in such applications as steel mills, excavators, and automatically-directed artillery,