STABILITY OF OPERATION OF ROTARY CONVERTERS 217 



case of synchronous motors, there appears an E.M.F. which is in 



2 



advance of the E.M.F. e and which is equal to wL'J (/:). But AI W 

 is itself negative (being equal to AD'AD=DD'); therefore, this 



E.M.F. (AF) is - behind the E.M.F. e. This E.M.F. here tends to 



2 



diminish the increment of 7^, but it increases I w still more. 



The ampere-turns by which the E.M.F. s is induced are equal to 



KN' 

 - Id, in which AJ represents the ampere-turns due to the 



constant excitation. It is seen at once, that whether the point C 

 be at the right or at the left of the line of reference (BY] for current- 



Axis of Reference for LM.F's. 



O 1 At 



values, the value of the excitation for an increment of Id is always 



KN' 

 equal to A a -\ -' J(/d); consequently, the excitation will increase in 



\/2 



all cases, and so will the E.M.F. e. 



The power developed at the shaft of the rotary converter, when 

 in normal operation is equal to 



When the increment of speed occurs, the increase of power developed 

 at the shaft is equal to 



In order to have stability of operation we should have AP<o. 



