5-B] 



TEST BY LOSSES. 



'53 



the frequency is higher than normal, complete data can be taken 

 as before. If the frequency is lower than that for which the 

 transformer is intended, the core loss and exciting current will 

 be greater and the voltage should not be raised so that they 

 become excessive for the transformer or the instruments;* W 

 should not exceed say twice and / four or five times their 

 respective values at normal frequency. It will be understood, 

 however, that these limits are only arbitrary. 



6. Curves for Exciting Current. For each frequency, plot 

 a curve showing the exciting current for different voltages, as 

 in Fig. 2. Locate by heavy black dots the two points accurately 



1.0 



.9 



.8 



,o.7 



0.605 Amp. = 3.03 percent. 

 I H =0.416 " = 2.0X 

 I J M = 0.439 "v*;20 



^-^ 



I = 0.430 Amp. =2.15 per cent 

 / H =0.320 " =1.60 " 

 J M =0.287 ' =1.44 " " 



40 



100 



120 



140 



VOLTS 



FIG. 2. Observed exciting current for varying voltage at different frequen- 

 cies; 2 K.W. transformer, loo-volt coil. To obtain the exciting current for 

 the 2,ooo-volt coil, divide these values by 20. 



* (5a). The current coil of the wattmeter has a certain rated current 

 carrying capacity which should not be exceeded for any length of time. 

 It may, however, be exceeded for a few moments only by 30 or even 40 

 per cent.; readings are taken quickly and the wattmeter is then cut out. 





