2 54 PHASE CHANGERS, ETC. [I.xp. 



amperes, and secondary for 10 volts X 1000 amperes. In method 

 (a), the secondary output is limited to 10 volts X 1000 amperes, 

 or 10 kilowatts. In method (), the potential may be varied 

 from 90 to no volts, which with 1000 amperes gives an output 

 of about 100 kilowatts. In practice, method (b) is therefore 

 used; in the laboratory, method (a) is often convenient when the 

 range of delivered voltage desired does not exceed E 2 . 



9. Again, to take care of a certain load as a transformer, 

 the regulator must have a capacity ( 2 / 2 ) equal to the load, 7 2 

 being load current and E 2 being load voltage. As an auto-trans- 

 former, the regulator will have a capacity (EJ 2 ) which is much 

 smaller, 7 2 being load current and E 2 the increase or decrease 

 of voltage (see Fig. 2) ; thus, if the voltage is to be raised or 

 lowered 10 per cent., the capacity of the regulator needs to be only 

 10 per cent, of the full load of the feeder. 



10. Further Experiments. The regulator may be tested under load, 

 either inductive or non-inductive, as in Exp. 5-A; or its performance can 

 be predetermined, as in Exps. 5-B and 5-C. 



The air gap necessitates a larger magnetizing current than in a trans- 

 former with a closed magnetic circuit; and, on account of larger leakage 

 reactance, gives poorer regulation and a smaller diameter to the circle 

 diagram. 



ii. Tertiary Coil. As the secondary coil moves away from the influence 

 of the primary and comes more nearly to the neutral position, it includes 

 less and less of the primary flux; the secondary leakage flux now causes 

 the secondary to act more and more as a choke-coil in series with the load, 

 thus giving a low power factor. This has been overcome by a short- 

 circuited tertiary coil, wound midway between the primary windings, so 

 located that it is not cut by the primary flux. As the secondary moves 

 away from the influence of the primary, the short-circuited winding comes 

 into play, acting similarly to a short-circuited secondary on a transformer, 

 so that the choking effect of the secondary or series coils becomes less and 

 less, and is practically zero in the neutral position. (See citations, 43; 

 also Standard Handbook, 6-158.) In a polyphase induction regulator no 

 tertiary coil is needed (Standard Handbook, 6-161). 



12. (2) Induction Regulator as Phase-shifter. Supply the 

 primary with polyphase current at normal constant voltage. The 

 secondary voltage will be found to be constant in value for all 



