3 -A] CHARACTERISTICS. 7 1 



can be illustrated by the following tests, or by modifications which 

 may be devised by the experimenter. 



1. Load the alternator on inductive load, using for this any one 

 particular load which can be conveniently obtained. An induction 

 motor can be used for a load, as in commercial practice ; but a choke 

 coil will serve fully as well. 



With the same speed and excitation as were used in taking the 

 external characteristic on non-inductive load, Fig. 4, take readings* 

 of load current and terminal voltage with the inductive load. These 

 readings are plotted,f in Fig. 4, as the point p, which is one point on 

 a characteristic for low power factor. (For more complete curves, 

 see Fig. 7, Exp. 3-6.) 



Throw off the load and ( at the same speed and excitation) read 

 the no-load voltage; the per cent, increase in voltage when the load 

 is thrown off gives the per cent, regulation. 



2. With the same speed and excitation, repeat with a non-inductive 

 load, so adjusted as to obtain the same load current as in I. 



Note the terminal voltage under load, the no-load voltage when the 

 load is thrown off, calculate the regulation and compare with the 

 regulation in I. 



3. With the same speed and terminal voltage as were used for 

 obtaining the armature characteristic on non-inductive load, Fig. 5, 

 note the increase in field current required with inductive load to 

 maintain constant terminal voltage and plot the point q, Fig. 5. 



4. Repeat with a non-inductive load (adjusted for the same load 

 current) and compare results. 



15. Efficiency. If the alternator is driven by a direct current 

 motor, the friction and core loss are conveniently determined by the 

 method of 21, Exp. 2-B. If the driving motor is alternating, a 

 wattmeter is used to measure its input, the increase in motor input 



* ( 143). If a wattmeter reading is also taken, the power factor can be 

 found by dividing the reading of the wattmeter by the product of current 

 and voltage. 



t(i4b). Since the same value of exciting current may at different 

 times give different amounts of magnetization (as in the case of the 

 ascending and descending curves), the point p thus located and the point 

 q as located later may not be exact in their positions, as compared with 

 the characteristics previously taken. They will, however, serve to illus- 

 trate the effects in question. 



