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ELECTRICAL MACHINERY 



The operation may be understood by reference to Fig. 

 194, which shows a simplified cross-section of a constant 

 current transformer. The leakage flux is shown in dotted 

 lines, and the leakage path is made noticeably large in such 

 a transformer. 



Principle on which Operation Depends. The weight 

 used for counterbalancing the secondary is not quite 

 sufficient to make the coil float, but, of course, when the 

 secondary is carrying current, the leakage lines repell the 



coil and help the counter 

 weight to make the coil float. 

 This force of repulsion is 

 proportional to the current 

 and the coil is under-counter- 

 balanced to such an extent 

 thai when the rated secondary 

 current is flowing the coil 

 floats. If more than rated 

 secondary current flows, the 

 secondary is repelled farther 

 from the primary, so that 

 more leakage flux is pro- 

 duced. But the more leak- 

 age there is the lower is the 



secondary voltage and so the secondary current lowers 

 and reduces to its proper value. 



Illustration of the Action. Suppose the transformer is 

 operating on a certain load of series arc lamps and one 

 lamp goes out, thus reducing the resistance of the external 

 circuit. The secondary current will immediately increase, 

 thus increasing the repelling force between the secondary 

 and primary and raising the secondary coil. But this 

 decreases the generated e.m.f. in the secondary coil because 

 of the increase in leakage flux and so the secondary current 

 decreases to its normal value. Hence we see that this type 

 of transformer will give a constant secondary current so 



FIG. 194. Flux Distribution in a 

 Constant-current Transformer. 



