CLASSIFICATION AND NOTATION. xi 



b. Auto-transformers, also called compensators : i. e. t sta- 

 tionary induction apparatus in which part of the primary winding 

 is used as a secondary winding ; or conversely. 



c. Potential regulators, or stationary induction apparatus having 

 a coil in shunt, and a coil in series with the circuit, so arranged 

 that the ratio of transformation between them is variable at will. 



These may be divided into the following types, or combinations 

 thereof : 



1. Compensator potential regulators, in which the number of 

 turns of one of the coils is changed. 



2. Induction potential-regulators, in which the relative posi- 

 tions of primary and secondary coils is changed. 



3. Magneto potential-regulators, in which only the direction 

 of the magnetic flux with respect to the coils is changed. 



d. Reactors, or reactance coils, formerly called choking coils : 

 i. e.j stationary induction apparatus used to produce impedance 

 or phase displacement. 



VI. ROTARY INDUCTION APPARATUS, which consist of primary 

 and secondary windings rotating with respect to each other. 

 They comprise : 



a. Induction motors. 



b. Induction generators. 



c. Frequency converters. 



d. Rotary phase converters. 



NOTATION.* 



The following table shows the more important symbols used 

 in this text and explains their meaning. A few of these symbols 

 are used at different times to represent different quantities. Thus 



* Non-standard symbols which are used but once or twice in this treatise are not 

 given in this table. The significance of such symbols is fully explained whenever 

 and wherever they are used. 



