V-B] INDUCTION REGULATORS. 251 



feeder. The potential regulator is a variable-ratio transformer 

 or auto-transformer used to raise the voltage as a booster, or 

 to lower the voltage as a negative booster. The regulator may 

 be operated either manually, or automatically by means of a 

 small motor which is controlled* by potential wires from any 

 desired point in the system. 



Alternating current potential regulators are of two types, the 

 step-by-step regulator and the induction regulator. 



3. The Step-by-step Regulator. The step-by-step regulator 

 is an auto-transformer (or transformer) with switching arrange- 

 ments for changing the number of turns. In principle it is the 

 same as any auto-transformer (Exp. 5~A). In practice, the 

 switching arrangement may consist of a number of individual 

 knife switches, but more usually is either of a drum or a dial 

 pattern, operated either manually or automatically. In the drum 

 or dial pattern, resistance or reactance in the contact leads is 

 sometimes used so that the contact arm can temporarily bridge 

 two contact points without disastrous short circuit. 



The step-by-step regulator is not easily made automatic. The 

 contacts deteriorate, even when arcing tips are used, and hence 

 this type of regulator is better for occasional than for constant 

 adjustment. For continuous automatic adjustment, the induc- 

 tion regulator is generallyf used. 



4. The Induction Regulator. An induction regulator is a 

 stationary transformer with a movable primary or secondary 

 which may be set in different positions for obtaining potentials 



wasted. Reactances are satisfactory for some cases; to be effective, how- 

 ever, they must be large and expensive. 



* (2b). The motor may be either direct or alternating and is usually 

 controlled through a relay, one form ot Tirrell regulator being made for 

 this purpose. 



t(3 a )- In cases where very rapid continuous automatic adjustment 

 is required, the induction type can not be used on account of the heavy 

 mass to be moved. An automatic regulator of the step-by-step type is 

 better for this rapid adjustment, because the moving part is only a light 

 contact arm. 



