34 THE DESIGN OF STATIC TRANSFORMERS 



with manufacturers of dynamos and motors, since high perme- 

 ability is of much less importance in the case of transformers 

 owing to the relatively low densities at which the cores are 

 usually worked. Transformers for use on circuits of very low 



2O 25 3O S5- -4O 



Ampere Turns per Cm of Lengtn of (/ore 

 FIG. 10. Saturation curve of representative sheet steel. 



periodicity constitute an important exception to this gene- 

 ralisation, and the material for such transformers should be 

 carefully specified and tested with respect to its permeability. 1 



1 Methods of testing sheet iron and sheet steel are treated at considerable 

 length in Chapter II. of Hobart and Ellis "Armature Construction" 

 (Whittaker & Co., London). These methods are as applicable to material 

 for transformers as to armature laminations. 



