7-B] INDUCTION REGULATORS. 255 



positions of the rotor (instead of varying as in the preceding 

 tests), but to be of varying phase, having a definite phase posi- 

 tion for each position of the rotor. This should be explained and 

 demonstrated experimentally. 



To do this, connect one primary circuit and one secondary cir- 

 cuit in series as before, measure E^ and E 2 separately, and E the 

 sum of the two for each position of the rotor, and construct 

 triangles on a common base E 19 as in Fig. 4, which illustrates the 

 varying phase* of E 2 . Observe 

 the relation between mechanical 

 and electrical degrees, noting, 

 for example, the mechanical 

 angle through which the rotor is 



FIG. 4. Voltage relations as phase 

 turned to shift the phase of E 2 shifter. 



by 45 electrical degrees. 



Although of little commercial use, this method is extremely 

 useful in the laboratory. If the primary supply is symmetrical 

 and of constant voltage, the secondary voltage on open circuit 

 will be constant and its phase angle will vary exactly with the 

 position-angle of the rotor, which can be read with a suitable 

 scale. A secondary load will, however, distort these conditions, 

 so that the scale reading will not give the phase exactly. 



The varying resultant potential E, in Fig. 4, shows that with 

 polyphase supply the apparatus can also be used as a potential 

 regulator, to be discussed in the next paragraph. 



13. (3) Polyphase Potential Regulator. The primary is 

 supplied, as in (2), with polyphase current at normal constant 

 voltage. The secondary coils for each phase must be separate 

 from each other, one secondary coil being connected in series 

 with each delivery circuit. For a 3-phase regulator (or 3~phase 

 motor used as a regulator) the connections are shown in Fig. 5. 

 The supply circuit is connected to the terminals I, 2, 3 of the 

 primary which may be star-connected, or delta-connected as 



* This can also be shown by a phase-meter. 



