46 TIIK D1KECT-CUKKKM MOTOK CH. Ill 



CHAPTER III 



EQUATIONS FOR THE INDUCTION FACTOR 



WE shall now show how to find the induction factor of a 

 motor that has to fulfil certain specified conditions. 



The problem may be stated in the most general way 

 as follows : Given the tension E of the line, the resistance It 

 of the motor, n the revolutions per second of the motor, 

 and w the rate of doing work expressed in watts, to find 

 the induction factor. 



If c is the current passing in the motor when fulfilling 



Tjl _ 73 



the required conditions, we know that 3/= - . Now 



n 



w = cMn, hence M= -- --, and we get the quadratic 

 n Mn* 



There are two possible values for M, the one a high 

 value obtained by taking the positive sign, the other a low 

 value given by taking the negative sign. Of these two we 

 shall select the former as giving the smaller current. 

 Note that w is the total rate of working, and includes all 

 torque losses. 



