20 



ELECTRICAL MACHINERY 



revolves and so hysteresis loss must occur. That this is 

 the case may be determined by measuring the amount 

 of power required to rotate the armature core with and 

 without a magnetic field on the machine. In a small gen- 

 erator a test showed that the power required to drive the 

 armature around when the magnetic field of the machine 

 was excited was 200 watts greater than that needed when 

 there was no magnetic field. Practically all of this 200 



Mi gneto Ik oti 



Hy er sis Loop 



for Cast S eel 



eresi 

 Cast 



Seel 



FIG. 2. Hysteresis Curve for Steel. 



watts of power was used up in the armature core as hysteresis 

 loss; the heat due to this loss was sufficient to raise the 

 temperature of the core several degrees. 



To keep the hysteresis loss in a machine low, specially 

 annealed iron or some special alloy steel is used. That 

 steel giving the hysteresis loop of least area is the one 

 which gives least hysteresis loss. 



10. Generation of E.M.F. in a Conductor Cutting Flux. 

 That an e.m.f. is generated in a conductor when it is so 

 moved that it cuts the lines of a magnetic field was first 



