Ans. It is somewhat altered as explained in figs. 2,058 and 2,059.
Reactance Method.—This consists in inserting inductance in the supply circuit and running the load current through a few turns around the field cores. This method is sometimes called compounding, and as it is automatic it is generally used where there is a rapidly fluctuating load.
Fig. 2,061.—Westinghouse 300 kw., 1,500 volt, three phase, 25 cycle, commutating pole rotary converter. The illustration shows clearly the commutating, and main poles and the relative sizes, also arrangement of the terminal connections.
If a lagging current be passed through an inductance, the collector ring voltage will be lowered, but will be raised in case of a leading current. The degree of excitation governs the change in the phase of the current to the converter, the excitation, in turn, being regulated by the load current. Accordingly with series inductance, the effect of the series coils on the field of the converter is quite similar to that of the compounding of the ordinary railway dynamo.
Multi-tap Transformer Method.—The employment of a variable ratio step down transformer for voltage regulation is a non-automatic method of control and, accordingly, is not desirable except in cases where the load is fairly constant over considerable periods of time. It requires no special explanation.
Fig. 2,062.—Mechanical oscillator and speed limit device of Westinghouse commutating pole rotary converter. It automatically prevents the armature of the converter remaining in one position and thus not allowing brushes to wear grooves in both commutator and collector rings. The oscillator is a self-contained device carried at one end of the shaft. The operating parts consist of a hardened steel ball and a steel plate with a circular ball race, backed by a spring. The machine is so installed with a slight inclination toward the end carrying the oscillator. As the armature revolves the ball is carried upward and owing to the convergence of the steel race and shaft face, the spring is compressed. The reaction of the spring forces the armature away from its natural position and allows the ball to drop back to the lowest point of the race.
Synchronous Booster Method.—This consists of combining with the converter a revolving armature alternator having the same number of poles.