10 THE DESIGN OF STATIC TRANSFORMERS 



and although I have designed large numbers of transformers 

 during the last fifteen years, nevertheless the prospect as 

 regards as-yet-un worked possibilities broadens with each 

 successive year, and I am each year more certain that the 

 subject of transformer design cannot be covered by the 

 enunciation of rules, formulae and constants, but that the 

 designing of a transformer or of a line of transformers for anv 

 particular rating or ratings still affords, and will for many 

 years continue to afford, ample scope for careful thought and 

 work. It is not in contradiction to this view that I put forward 

 in the course of this treatise various rules and tables, but 

 rather that they may be employed as rough starting points, 

 and in the full realisation that it is often not only expedient, 

 but in the interests of obtaining the best results that wide 

 departures from these preliminary indications should be made 

 as the design proceeds. 



I should like to direct special attention to the almost pre- 

 dominating importance in transformer design and construction 

 of the selection and testing of materials. We have to consider 

 not only that the materials shall be initially of the correct 

 quality, but that they shall not " age." It was Mr. G. W. 

 Partridge who, some twenty years ago, first directed attention 

 to the " ageing of transformers." No less important is the 

 question of deterioration of the insulating materials, and of the 

 cooling oil in which the transformer is immersed. There are 

 also exceedingly difficult questions of the effects of the oil on 

 the insulating materials, and these effects render certain other- 

 wise-excellent insulating materials quite unsuitable for oil 

 transformers. 



The Epstein method of testing iron has been adopted in 

 Germany and constitutes the basis for contracts for the supply 

 of core plates. In this country contracts are much less definite 

 on this point, and it would be of great advantage to adopt 

 the Epstein method. 



The present treatise should be regarded as merely an intro- 



