August 9, 1906] 



NA TURE 



347 



establish exact diagrams which will cover all types 

 of motors. It may be possible to achieve this, but 

 the task is not an easy one, and the solution offered 

 by the author can certainly not be accepted. Take 

 the two simple diagrams Figs. 32 and 33 ; the first 

 illustrates the action of the motor shown in Fig. 30, 

 the second (which is not referred to in the text) is 

 probably intended to illustrate the action of the motor 

 shown in Fig. 31. The E.M.F. (J„W„) in Fig. 32 

 is responsible for the current J„ flowing in the short- 

 circuited rotor; it must therefore be the resultant of 

 all those E.M.F. 's which are effective so far as the 

 short-circuiting brushes are concerned. These 

 E.M.F.'s are E,., E„ E/, E/, and E;. When the 

 motor is standing, E,. and E,.' are nil, but they in- 

 crease in direct proportion with the speed, with the 

 result that J„W„ must, according to the diagram, in- 

 crease with the speed independently of the load ! In 

 other words, the rotor current J„ must increase with 

 the speed, consequently also the stator current J/. 

 Seeing that the machine is one with a series character- 

 istic, it is very obvious that the diagram in question 

 cannot be correct. In a machine of the kind the 

 tendency of the current is, of course, to diminish with 

 the speed. The fact of the matter is that the phase 

 of E,/ is shown incorrectly. If the direction of rota- 

 tion is such that E,. is in phase with the flux K„, then 

 E,.' must be of opposite phase to the flux K,, for 

 these fluxes are not only at right angles to each 

 other in space, but also nearly at right angles to 

 each other in phase. The presence of this very serious 

 mistake evidently prevented the author from grasping 

 the full meaning of the various vectors of his diagram. 

 (E,) must be considered as the (Working E.M.F. ; 

 (E/) is then the back E.M.F., (Ej'-fEi') represents 

 the self-induction of the rotor circuit, whilst E^ (and 

 not E/, as stated by the author on p. 32) must be 

 looked upon as the compensating E.M.F. It is nearly 

 opposed to (E,'-t-Ei'), therefore tends to cancel the 

 effect of the self-induction in the rotor and to bring 

 J„ more and more into phase with E;. Since E,. in- 

 creases with the speed, it follows that with increasing 

 speed the phase of J„ will approach that of E;, and 

 that the power factor will rapidly improve. 



The writer also fails to agree with the author's 

 Fig. 33. Owing to a mistake similar to that present 

 in Fig. 32, we get the following curious and im- 

 possible result. It is obvious that E,., which appears 

 at the brushes (aa), must be responsible for the flux 

 K,; ; it is generally admitted that a magnetic field 

 lags by about 90 degrees behind the E.M.F. responsible 

 for it, yet in Fig. 33 K, actually Ictids E^ by nearly 

 that amount. The author also ignores the fact that 

 for the arrangement of brushes shown in Fig. 31 we 

 have two currents in the rotor, the one flowing from 

 (b) to (b), the other from (a) to (a), the former being 

 the working current, the latter producing K, 



The value of the next fundamental diagram (Fig. 35) 

 is greatly reduced because the author mistakes, in 

 Fig. 34, the axis K„ for the axis K„ thus making 

 a comparison between Fig. 34 and Figs. 30 and 31 

 quite impossible. In Fig. 34 the motor-field axis K, 

 is the vertical axis, and not the horizontal, as has 

 NO. 1919, VOL. 74] 



been assumed by the author, so that E/ is not nil as 

 stated. No more is E, nil, although it is now im- 

 pressed on the rotor by conduction, and not by in- 

 duction, as in Figs. 30 and 31. 



The writer's space is limited, and he must there- 

 fore cut his remarks short. The fundamental 

 diagrams of chapter ii. having been proved to be 

 wrong, the value of the whole chapter is naturally 

 greatly discounted. The chapter, however, contains 

 a number of other mis-statements, some of which we 

 will note in passing. 



On p. 34 it is stated that the transformer flux in 

 a short-circuited transformer is zero ! On p. 42 that 

 the motor shown in Fig. 53 is compensated in the 

 same manner as the Winter-Eichberg machine, 

 whereas compensation is due to the alteration brought 

 about in the phase of the motor field by the intro- 

 duction into the exciting circuit of the auxiliary 

 E.M.F. derived from S,. In diagram 43 the E.M.F. 

 (E,.') is shown as being of opposite phase to the 

 E,.' of Fig. 32, although both diagrams refer to the 

 same motor. The remarks on commutation are 

 difficult to follow, because of the attempt to deal with 

 the various types of motors at one and the same time. 

 It is recommended that flux K„ should be chosen 

 low at starting for motors of the series induction 

 type, whereas it is the flux K,, which at that time 

 should be small. Contrary to the author's state- 

 ment, the commutation difficulties with polyphase 

 commutator motors are just about of the same order 

 as those met with in the series induction motor. In 

 dealing with the power factor (p. 59), the author 

 makes a statement in the last paragraph which re- 

 veals a great confusion of ideas. This mistake prob- 

 ably arises out of the confusion of the axes of K, 

 and Ka already pointed out in connection with 

 Fig. 34; in addition, the notation is now suddenly 

 changed. It is, however, evident that for the case 

 of the series conduction motor (Fig. 34) ^g stands 

 for the field coaxial with the armature brushes and 

 due to the armature ampere turns ; ig is perpen- 

 dicular to K„ and by neutralising /'„ as shown in 

 F'g- 37 o'' 39 '*^^ power factor is improved as 

 stated. But in a " repulsion " motor such as 

 Fig- 30, ^-g does not exist ; it is neutralised ipso 

 facto because the energy is conveyed into the rotor 

 by induction, and not by conduction as in Fig. 34. 

 Furthermore, if ig did exist, it would be coaxial 

 with K„. If ig is a misprint for K,„ then by 

 neutralising it the torque of the motor would be 

 destroyed, for K, is the !iw/o> field. .As to speed 

 regulation, and contrary to the author's opinion, any 

 so-called repulsion motor can be satisfactorily con- 

 trolled by suitably influencing the rotor circuits. 



Chapter iii. only deals with motors full descrip- 

 tions of which have appeared from time to time in 

 the technical Press. As to the notes on the pre- 

 determination of alternate-current commutator motors, 

 these are very superficial, and mainly apply to the 

 series conduction machine. 



On the whole, the book is more likely to bewilder 

 the reader than teach him anything; it ought to be 

 very thoroughly revised and corrected before it can 



