130 THK DIRECT-CURRENT MOTOR < II. VI 



armature of the tested dynamo due to hysteresis ;m<l eddy 

 current torque. 



A test of a 14 horse-power motor gave the following 

 results : Total torque loss at 1,500 r.p.m., 37 inch-pounds. 

 Friction, 14 inch-pounds; hysteresis, 7 inch-pounds; 

 whence we deduce 16 inch-pounds as the eddy current 

 loss. This motor took 5 - 2 amperes when running at no 

 load on a line of 1 25 volts tension. The value of M was 5. 



Fig. 32 gives the losses in a 15 horse-power motor at 

 different loads. The machine is a four pole belt type 

 Crocker- Wheeler motor, shunt wound, and designed to run 

 at 800 r.p.m. on a 230-volt circuit. The O*R losses in the 

 magnet winding given in this diagram are included in the 

 total losses. 



The hysteresis loss may be found by turning the 

 armature slowly with a spring balance attached to a lever, 

 and deducting for friction. 



If the energy required to turn one cubic centimetre of 

 iron through one complete cycle, in a magnetic field of 

 given strength, is k ergs, the energy expended in rotating 

 an armature containing v cubic centimetres, through one 

 revolution, is h s v, if s is the number of complete cycles 

 per revolution. If the armature be turned through n 

 revolutions per second, the energy expended per second, 

 that is, the rate of working, is Jisvn, and the watts is equal 

 to hsvn 10~ 7 . Tables of h for different values of B are 

 given in most text-books on magnetism. If i is the torque 

 in inch-pounds. v:= 71 / n, hence we get : 



/ = l-4l/**t;10- 7 (55). 



Example 32. A 10 pole dynamo has 621 x 10 3 

 cubic centimetres of iron in the armature. The maximum 



