1903.] The " Hunting " of Alternating- Current Machines. 

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FIG. 2. 



247 



Rough determinations were made of the various constants of the 

 machine ; the resistance measured in the ordinary way was found to 

 be 0*55 ohm cold. In normal working the resistance averaged about 

 0*7 ohm, making a total of 0'8 ohm with the resistance in the mains. 

 The self-induction L, or that part of the induction which is linked with 

 the armature but not with the field coils, was measured by observing 

 the drop of potential across the armature when passing an alternating 

 current, the field coils being short-circuited so as to eliminate the 

 induction linked with them. The apparent resistance was assumed to 

 be ^(Ly + /o 2 ). The result was that Lp varied from 0'65 0'93 ohm, 

 according to the position of the armature. We take 0'8 ohm as the mean 

 value of "Lp, making 0'92 ohm total reactance with the reactance in the 

 mains. For the determination of * the machine was run as a generator 

 on various non- inductive resistances varying from nothing up to 3 ohms. 

 It was assumed that if V be the open circuit potential, C the current 

 [ v^mean 2 ) in each case] and R the total resistance including armature, 

 then V = C v/[(L + K) 2 jo 2 + R 2 ]. So determined the value of (L + K)p 

 was found to range from 1'3 ohms in the first case (short circuit) to 

 1-1 ohms in the second. 



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