Ques. What is the behavior of a rotary converter when hunting?
Ans. It is liable to flash over at the direct current brushes, which is common in high frequency converters where there are a great number of poles and the brushes are necessarily spaced close together around the commutator.
Ques. Is this fault so pronounced with motor generator sets?
Ans. The motor generator operating on a high frequency circuit, the generator can be designed with a few poles and the brushes set far apart which will greatly reduce the chance of flashing over.
A synchronous motor will drive a generator at a constant speed during changes in load on it, and by having a field regulating resistance it can be used to improve the power factor of the system.
When an induction motor is used its speed drops off slowly as the load comes on the generator, and it is necessary to regulate the voltage of the generator by means of a field rheostat, or compound wound machines may be used.
While an induction motor requires no separate excitation of the field magnets like the synchronous motor, its effect on the power factor of the system is undesirable.
Although it is seldom necessary to convert direct current to alternating, such an arrangement of a direct current motor driving an alternator is often justified in place of an inverted rotary converter, as in this case the alternating current voltage can be changed independent of the direct current voltage.
The racing of an inverted rotary under a heavy inductive load or short circuit does not take place in motor generator set mentioned above.