218 



ALTERNATING CURRENTS 



currents in the primary and secondary flow in opposite direc- 

 tions (Fig. 209). Therefore, there is repulsion between the 

 two coils. Assume that the load changes, for example it de- 

 creases. This change of load would be produced by short-circuit- 



Dashpot 



Ammeter 



Weight 



FIQ. 208. Constant-current transformer. 



ing one or more lamps, causing a decrease in the load resistance. 

 Because of the decreased load resistance, first the secondary 

 and then the primary current tends to increase. This increases 

 the repelling force between the two coils, resulting in the secon- 

 dary moving further away from the primary. The leakage flux 



between the two coils is thus increased 

 and this reduces the secondary induced 

 The secondary coil will move 

 from the primary until the 

 current is again at its 

 The action of such a 



^Secondary 

 Leakage Flux VOltS. 



away 



if- Mutual Flux * 



secondary 

 normal value. 



Primary 

 Leakage Flax 



transformer depends on the change 



in leaka e flUX f 



n acon- 

 stant-current transformer. Secondary, as IS shown in Fig. 209. 



Because of its large proportionate 



leakage flux this type of transformer has a very low power- 

 factor except at or near its maximum load. This is one objec- 

 tion to its use. 



