476 Pupin — Resonance Analysis of Alternating Currents. 



The general conclusions of this group of experiments may 

 be summed up as follows : 



I. A ferric self inductance in circuit with an alternator 

 which gives a simple harmonic electromotive force distorts the 

 current by introducing higher odd harmonics, principally the 

 harmonic of three times the frequency of the fundamental. 



II. This harmonic (and in all probability all other harmon- 

 ics) increases at the same rate as the fundamental when the 

 excitation increases, the rate of increase being up to JfOOO C. G. 

 S. lines of force per sq. centim proportional to the intensity of 

 magnetic induction. 



III. When this ferric inductance is a transformer then the 

 distortion appears in the induced secondary electromotive 



force, if the transformer has an open magnetic circuit, it does 

 not appear there (to any extent worth considering) if the 

 magnetic circuit is a closed one. 



IV. A practically simple harmonic electromotive force is 

 produced by alternators with smooth core armatures when 

 symmetrically wound, even if the machine is worked at con- 

 siderable degrees of magnetization of the armature core. 



B. Experiments with alternator of slotted core armature type. 



The machine employed in these experiments was the 1 H. P. 

 alternator mentioned above. It is a 16 pole machine with 

 slotted armature core. It gives at full excitation and the speed 

 at which it was usually run in these experiments about 1500 

 volts.* The transformer connected with it was of induction 

 coil type with a cylindrical iron core made up of very care- 

 fully insulated fine iron wire. The same series of experiments 

 were performed as under group (A). The first series in this 

 group gave exactly the same results as the corresponding series 

 in group (A). The excitation varied from one-seventh of the 

 full to full excitation ; the amplitude of the fundamental and 

 the first odd harmonicf varied at the same rate during the 

 whole interval, so that a parallel pair of straight lines like 

 those in fig. 5 could be plotted in this case also. The second 

 series resulted in the conclusion that the harmonic was very 

 strong and due, in a very large measure, to the action of the 

 armature and not to that of the transformer as in the other 

 case, although the transformer, also, contributed a distinct but 



* A more complete description of this machine and the transformer will be 

 found in this Journal, June, 1893, p. 510, etc. Owing to an accident which 

 somewhat impaired the insulation of the armature the machine was run last year 

 at low excitation and heDce low voltage although the speed was then considera- 

 bly higher. 



f The second odd harmonic, that is the harmonic whose frequency is five times 

 that of the fundamental was there but weak. 



