On Synchronous Motors, Hunting Lightly (ElectroMagnetically Lightly)

Abstract

Lately, the writer gave on this journal an essay on synchronous motors in violent hunting, under the title of "Experimental Study on the Hunting of Poly-phase Synchronous Motors". In this note, he has studied further on hunting which is electro-magnetically light, i.e. when the linkage flux is not so much diminished by the hunting.
The relation between the change of r.p.m. and the corresponding increase of input current is studied in such case. For under excitation, it is same as in the case of violent hunting, with similar curve as magnetization B-H curve.For over excitation, the curve of the relation shows also the same form, but of different inclination. For medium excitation, the increase of input current due to corresponding changes of r.p.m., is situated between the above said curves of the shape as B-H curve. Thus, as increasing the excitation from under to over degree, the increase of input current rounds a loop, (along up one B-H curve, to another B-H curve and then along down another B-H curve), during which the corresponding change of r.p.m. increases and decreases. Hunting of current produces some oscillation of phase angle. For violent hunting, the mean phase angle of such oscillation is always in lag. But in our case, this mean phase angle is not so different from that of steady condition.
Some theoretical explanations and conclusions are also given in this note.