178 



THE TRANSFORMER. 



hammering which it undergoes while being wound on to the 

 former. 



In consequence of the resulting uncertainty of the resis- 

 tance of the windings, an agreement within 20 per cent, 

 with the resistance of the standard transformer might be 

 taken as sufficiently near. On the other hand, transformers 

 intended to work in parallel must have the same ratio of 

 transformation at all loads, and must consequently have 

 practically equal resistances in the windings. In testing 

 their suitability for working in parallel, use is made of the 

 fact that a heavy circulating current will flow between the trans- 

 formers when connected in parallel to the same circuit if 

 their secondary voltages are not exactly equal. A rapid 

 test of a series of transformers as regards equality of ratio 

 of transformation may be made as described in the following 

 experiment. This experiment is to be considered rather as a 

 rough and practical test of the uniformity of a series of machines 

 for use in the factory test-house, than as an experiment for 

 giving information as to the characteristics of the machines 

 individually 



EXPERIMENT XXXIII. TEST OF UNIFORMITY OF RATIO 

 OF TRANSFORMATION IN A SERIES OF SIMILAR TRANSFORMERS. 



DIAGRAM or CONNECTIONS. 



J 



M I} M r Source of alternating current. 

 T v T. 2 , T s . Transformers to be tested for equality of 



transformation ratio. 

 A. Low reading ammeter. 



T l is shown as the transformer taken as the standard of 

 comparison. The leads fr,om it are to be ultimately con- 

 nected to all the other transformers in turn. 



