Amplidyne regulating systems

The amplidyne is a cross-field-excited d.c. generator, in which the field input is much smaller than that of a normal generator. Because of this property it can be used as an automatic regulator for a wide variety of industrial equipments. In such an equipment, the amplidyne is generally used as an exciter for a larger machine or combination of machines, such as a.c. or d.c. generators or motors, or intermediate exciters. In this way a large output can be controlled from the amplidyne field current. In order to obtain automatic regulation of any quantity, the quantity is matched against a constant reference, and the difference is used to excite the amplidyne so as to correct any change, thus forming a closed-cycle control system. A high accuracy of regulation under steady conditions can easily be achieved in this way. Under transient conditions, the behaviour of the equipment is a matter of changes relative to the steady state, and can be investigated by means of an equivalent system diagram from which all steady voltages are omitted. A typical equivalent system consists of a chain of amplifying stages with a feedback circuit connecting the output of the last stage to the input of the first stage. With the aid of this equivalent diagram the nature of any oscillations which may occur can be investigated. This method of attack is of general application for any type of continuous regulating device, and has proved of particular value for amplidyne regulators. The factors governing the accuracy, stability and speed of response are discussed in relation to the whole system and to each component, as well as the effect of additional apparatus such as anti-hunt transformers and ballast resistors.