VOLTAGE REGULATION 



255 



150. Voltage Regulation of Rotary Converters 



A very important problem in connection with converters is that 

 of voltage regulation. The voltage ratio is approximately constant, 

 and is but little affected by altering the exciting current. Hence 

 the voltage of a rotary converter cannot be controlled (except within 

 extremely narrow limits) by the method commonly in use with 

 continuous-current generators that of varying the field excitation. 

 A marked change in the voltage on the continuous-current side can 

 only be obtained by changing the alternating voltage. The two 

 methods commonly in use in practice for effecting this change are 

 (1) the hand regulation method, involving the use of an induction 

 regulator, and (2) the automatic method, depending on the use of 

 choking coils and a compound winding on the converter field. 



The induction regulator method is mostly in use where the con- 

 verter supplies a lighting load, in which case very perfect voltage 

 control is desirable. An induction regulator is essentially a poly- 

 phase transformer with movable primary. In construction, it is 

 identical with a polyphase induction motor whose wound rotor 

 represents the primary, the stator carrying the secondary winding. 

 The rotor is normally held fast, and can only be slowly rotated in 

 either direction by means of worm gearing driven by a small auxiliary 

 induction motor mounted on the top of the regulator case. In one 

 of the extreme positions of the primary, the rotating magnetic fields 

 due to primary and secondary are in exact coincidence of phase, 

 while in the other extreme 

 position they are in direct 

 opposition of phase. 



The diagram of connec- 

 tions corresponding to one 

 phase is given in Fig. 157. 

 The primary of the induc- 

 tion regulator is connected 

 across the corresponding 

 phase of the converter arma- 

 ture, while the secondary 

 is in the main circuit. Let 

 us suppose that with a 

 certain current passing into 

 the converter the primary 

 of the induction regulator 

 is rotated in such a direc- 

 tion as to increase the separation of phase between the primary 

 and secondary hypothetical fields. Now, so long as the secondary 



SC CON DAM 

 Of 



INDUCTION 

 REGULATOR 



FIG. 157. Connections of Induction Regulator. 



