(HAP. Ill] HYSTERESIS AND EDDY CTKKKNTS 49 



tions to use B in kilolines per square centimeter, and V in cubic 

 teters. In this case the constant 10~ 7 is not necessary (see 

 Prob. 17 below) ; but the student must now remember to multiply 

 by 6.31 the values of r/ found in the various pocketbooks. 



1 1 > steresis loss cannot be represented always with sufficient 

 accuracy by formula (21) or (20) over a wide range of values of B, 

 because the exponent n itself seems to increase with 11. Whciv 

 greater accuracy is required at medium and high flux densities the 

 i nl lowing formula may be used: 



In this formula the term with B 2 automatically becomes of more 

 and more importance as B increases. By selecting proper values 

 and r/' a given experimental curve of loss can be approxi- 

 mated more closely than by means of formula (21). On the other 

 hand, formula (21) is more convenient for comparison and anal\>is. 

 Curves of hysteresis loss and values of the constant ij will be 

 found in various handbooks and pocketbooks. It is hardly worth 

 while giving them here, because hysteresis loss varies greatly with 

 the quality of iron and with the treatment it is given before use. 

 Moreover, the quality of the iron used in electrical machinery is 

 being improved all the time, so that a value of TJ given now may 

 be too large a few years from now. 



Considerable effort is being constantly made to improve the 



quality of tin- iron used in electrical machinery so as to reduce its 



hysteresis loss. The latest achievement in this respect is the pro- 



n of the so-called silicon steel, also called alloyed steel, which 



contains from 2.5 to 4 per cent of silicon. This steel shows a much 



lower hv.-trresis loss than ordinary carbon steel. Incidentally, 



the el sistivity of silicon steel is about three times higher 



that of ordinary steel, so that t he e<M\ -current loss is reduced 



about three times. The advantage that silicon steel has over car- 



bon steel is clearly seen in Fig. 10. Silicon steel is largely used 



:ansformer cores because it permits the use of higher flux 



,n. 1 therefore the reduction of the weight and cost of a 



transformer, in spite of the fact that silicon steel itself costs more 



-ram than carbon steel. 



Another great advantage of silicon steel is that it is practically 



.''/"/: this means that the hysteresis loss does not increase 



with n increase in the hysteresis loss of n transformer 



