SATURATION TESTS 



17 



the armature directly under the center of the brushes 

 of two adjacent studs, all other brushes being removed. 

 The galvanometer circuit should have a resistance 

 such that the voltage induced in the armature, when 

 the field is broken at a maximum current value and 

 reversed, is just sufficient to give the maximum scale 

 deflection on the ballistic galvanometer. 



A ballistic curve may then be obtained, from which 

 the running saturation curve can be readily derived. 

 Galvanometer readings are taken at a number of field 



/so. 



w- 



dmperes F/e/d 



Fig. 5. Ballistic and Runring Saturation on a 75 Kw., 125 Volt, 6-Pole, 

 375 R.P.M. Compound Wound D-C. Generator 



current values, as in the running saturation tests. The 

 magnetic flux due to each current value is proportional 

 to the induced voltage in the armature when the field 

 is broken and reversed by means of the reversing switch. 

 Hence, if the galvanometer deflections are plotted with 

 the field current, with the former as ordinates, a curve 

 similar to the running saturation curve will be obtained. 

 This curve bears a definite relation to the running 



