NA TURE 



THURSDAY, OCTOBER 8, iS 



THE ALTERNATE CURRENT 



TRANSFORMER. 



The Pnnciples of the Transformer. By Frederick 



Bedell, Ph.D. 8vo. Pp. xii + 400. (New York : 



The Macmillan Company. London : Macmillan and 



Co., Ltd., 1896.) 



IN a work coming to us from one of the principal 

 technical colleges in the United States, and on a 

 subject which has been occupying the attention of 

 electrical engineers for at least fourteen years, one would 

 naturally expect to find a wcU-considered treatment 

 based on the concentrated essence of practical experience, 

 and embodied in a form which should definitely guide 

 design and construction. It was therefore with a feeling 

 of disappointment that we found so large a portion of 

 this volume devoted to a class of investigations which 

 are nothing more than elaborate mathematical e.xercises 

 in the geometry of periodic quantities. The experimental 

 researches of numerous engineers and electricians in 

 the last decade have completely elucidated the general 

 nature of the operations going on in the alternate current 

 transformer, and as a practical art its construction has 

 been brought to a very high degree of perfection. The 

 demand for transformers has developed of late years an 

 entirely new branch of the iron industry, viz. the manu- 

 facture of transformer iron, on which much depends, and 

 with a large body of experience to fall back upon, the 

 manufacturer can now work up to a definite and exacting 

 specification. In the presence of other well-known text- 

 books which deal with the properties of periodic currents, 

 the general construction of the transformer, and its 

 employment in electric distribution, there was hardly 

 room for a volume of the size before us unless marked 

 by some distinct novelty of treatment, or the development 

 of a theory strictly brought to the test of experimental 

 confirmation. Unfortunately we find neither of these 

 two rec|uirements here fulfilled. The earlier portions of 

 the book are occupied with an elementary discussion of 

 the properties of simple harmonic currents. It may be 

 assumed that for students beginning to study the 

 properties of alternating currents some amount of this 

 information is necessary, but for the training of engineer- 

 ing students it is above all things necessary that the 

 fundamental definitions should be so laid down as to lead 

 immediately to clear notions of how the quantities con- 

 cerned are measured, and numerical examples be added. 

 This, however, is just what is not done in this book. 

 The definitions of such leading terms as magnetic 

 induction, magnetic force, inductance, coefficient of self- 

 induction, are given in a way which is likely to produce 

 a considerable amount of obscuration in the mind of a 

 beginner. Take as an instance the definition of the 

 coefiicient of self-induction of a circuit. He is told on 

 p. 35, it is the ratio of the induced electromotive force 

 in a circuit to the time-rate of change of the current 

 producing it. He then learns on p. 50, that the practical 

 unit is the Henry, which is 10'' C.G.S. units. He then 

 discovers that the C.G.S. unit of inductance is one 

 centimetre, and he is left to imagine how a ratio can be 

 NO. 1406, VOL. 54] 



measured in centimetres. This method of defining 

 inductance is much more artificial than that which is 

 based on notions of the energy associated with a current. 

 The general properties of simple harmonic currents flow- 

 ing in inductive circuits are then given, the arrangeinent 

 and selection of the matter following closely on the lines 

 of other existing English treatises on the same subject. 



The body of the book is occupied with the treat- 

 ment of the theory of the transformer. The author 

 apparently takes the transformer chiefly to be an air-core 

 transformer, with constant coetificients of self and mutual 

 induction, and expends an immense amount of pains in 

 solving various problems about this imaginary instrument, 

 elaborately worked out with polar diagrams and a lavish 

 use of algebra. 



The results, however, when done have very little real 

 use. Probably no transformer-maker that ever lived had 

 occasion to measure a coefficient of self-induction, and 

 the merest tyro ought to be told at the beginning of the 

 subject that this method of approaching its treatment 

 with the assumption of constant coefiicients of inductance 

 is but little use in connection with the actual iron-core 

 transformer of real life. The theory of the transformer 

 would be simplicity itself if the cyclic value of the in- 

 duction created in an iron-core transformer by a periodic 

 magnetising force could be simply expressed as a 

 function of the force. In our ignorance of what really 

 goes on inside iron when magnetised, all we are able to 

 do at present is to express the area of the hysteresis 

 curve in terms of its maximum ordinate, and no practical 

 progress is made by raising a whirlwind of mathematical 

 symbols around suppositions or premises not based on 

 experience. 



The chapters on alternate current curve tracing, trans- 

 former design, and testing, bring us more within touch of 

 practice ; but they are handled in a somewhat limited way. 

 The curve tracing is chiefly restricted to the now almost 

 obsolete hedgehog transformer, and the one instance in 

 which the design for a transformer is worked out in com- 

 plete detail is not confirmed by actual tests of the trans- 

 former so supposed to be made. These matters ought 

 really to have formed the bulk of the book. 



The good design of a transformer, like that of many 

 other appliances, is largely a matter of compromise and 

 experience. Full and exact details of actual transformers 

 built, and the tests of the same, would have given useful 

 information. As it stands, there is little or nothing 

 which would be the least use in the drawing-ofiice. A 

 student asked to design an impedance coil to pass a 

 current of fifteen amperes, and drop a pressure of sixty- 

 five volts, would find no information in this volume to 

 enable him to attack this simple problem with ease and 

 certainty. 



The fact is, that there are two ways of discussing a 

 subject such as that of the treatise before us. One way 

 is to collect all possible data from experiments and prac- 

 tice, and then develop from these a physical theory 

 which shall reconcile all the facts, and be a sufficient 

 guide to future practice. The other is to eliminate the 

 real difficulties by assumptions akin to that of the friction- 

 less pulley of applied mathematical text-books, and then 

 evolve by sheer force of deductive reasoning all possible 

 mathematical consequences. The latter method reduces 



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