2 5 PHASE CHANGERS, ETC. [Exp. 



EXPERIMENT 7-B. Induction Regulators.* 



i. Types of Potential Regulators. When a generator sup- 

 plies current either alternating or direct to a single line, the 

 desired voltage at a distant receiver can be maintained by vary- 

 ing the excitation of the generator, either by a hand-operated 

 rheostat or by some automatic device as the Tirrell regulator 

 (3a, Exp. i-B). This is also accomplished, to a certain ex- 

 tent, by a compound winding (4, Exp. i-B) or composite 

 winding ( ua, Exp. 3~A) on the generator. 



When, however, a generator (or several generators in paral- 

 lel) supplies several lines or feeders, with independently varying 

 loads, this simple method of regulation is no longer possible; 

 for at any particular time the voltage on one feeder may be too 

 high, while the voltage on another feeder is too low, and there 

 is no change of station voltage which can be made which 

 will bring the delivered voltages on all feeders to their proper 

 values. 



In direct current distribution systems, the proper voltage can 

 be approximately maintained by inter-connecting the various 

 feeders and proportioning the amounts of copper according to 

 average load conditions. In large stations, a step further is 

 taken by maintaining in the station several sets of bus bars at 

 different voltages, so that feeders may be supplied with the 

 proper voltage according to conditions, long feeders being sup- 

 plied with a higher voltage than short ones. Use is also made 

 of auxiliary batteries, motor-driven posters, etc. In early sta- 

 tions, wasteful series resistances in each feeder were sometimes 

 used. 



2. In an alternating current system, the most satisfactory 

 resultsf are obtained by the use of a potential regulator in each 



* Note that an induction motor with wound secondary can be used as 

 an induction regulator ; see 4. 



t (2a). Series resistances and reactances have been used for this pur- 

 pose. To use the former is not good practice on account of the energy 



