CH. XIII] 



CURRENT RECTIFIERS 



491 



FIG. 261. MERCURY ARC RECTIFIER, DIAGRAM OF CONNECTIONS. 



(Cut loaned by the General Electric Co.). 



The alternating current supply comes in at the upper part of the transformer. 

 This supplies alternating current at 220 volts (for a no volt arc) between the 

 points C and H. The arrows indicate the direction of flow of the current dur- 

 ing one-half of the cycle and the arrows enclosed in circles indicate the flow of 

 current during the other half of the cycle. Taking the time when H is the 

 positive pole of the transformer, the current flows down this wire and over to 

 the point A. Here the current flows through the tube to the cathode B, 

 through the battery J (or the arc lamp situated at J) to D. It then flows to 

 the right through E and up to G. 



When the current is reversed, current cannot follow this path because 

 between A and B the rectifier tube acts as a valve, as the mercury arc allows 

 current to flow towards B but never away from it, hence the current must flow 

 from G to A l to B through J to D, through the coil F to the left and up to the 

 point H. 



The function of the coils E and Fis to act as an auto-transformer, for without 

 them current could flow directly from G to H without passing through the 

 rectifier tube. In actual practice both coils E and F are wound on the same 

 iron core. 



