Short-circuit characteristics and load performance of inductor-type alternators

The paper develops a graphical method of determining the short-circuit current of an inductor alternator, taking into account the effect of a damping circuit which prevents oscillations of the total flux. It is shown that the short-circuit current depends mainly on the important ratio of maximum to minimum flux and on the leakage. The equivalent circuit for the inductor alternator is determined from the open-circuit voltage and short-circuit current. The ratio of these values varies owing to saturation effects, but can be taken as constant for a given excitation and independent of the load circuit. Compensation of the internal inductive reactance by series condensers for an alternator with constant and variable speed is considered, and the transient- and steady-voltage changes are investigated. The reason for the voltage drop of the fully compensated machine being many times greater than the resistive drop is given. The effect on the speed/torque characteristic of series-condenser compensation is shown. The paper explains that the damping winding increases the effective excitation for a load circuit having a lagging power factor and reduces for a leading power factor. An unusual type of instability arising when paralleling series-compensated alternators is investigated, and a remedy for this phenomenon is given.