164 



COMMERCIAL ELECTRICAL TESTING 



be applied to the low potential winding in order to avoid 

 placing meters in high potential circuits. Core loss 

 should always be taken from a sine wave alternator 

 and transformer connections made so that the alternator 

 is operated at normal excitation when normal potential 

 reading of core loss is taken. 



To make this test, estimate the capacity of the meters 

 required, connect the ammeter in circuit and take a 

 preliminary reading of exciting current to show what 

 meter capacity is required. Be sure to place the high 

 tension leads so that no one can come in contact with 

 them and that there is no danger of short circuit. The 

 instruments should be so placed that they have no in- 



W A 



D A C 

 Fig. 48 

 Connections for Core Loss Test 



fluence upon one another, and are not affected by any 

 stray field. 



A core loss curve should be taken, starting at 50 per 

 cent of rated potential and increasing the voltage to 25 

 per cent above normal. To do this, hold the frequency 

 constant and vary the voltage, taking simultaneous 

 readings of the excitation amperes and watts core loss. 

 Do not plot the curve as each reading is taken, but as 

 soon as all are finished. If the curve is not smooth, repeat 

 the test. The curve will be more satisfactory if meters 

 can be so selected that no change in them is necessary 

 throughout the curve. Record all meter numbers, their 

 constants and date of calibration, temperature of iron, 

 and numbers and ratios of potential transformers or of 

 multipliers. Wherever possible, use the wattmeter with- 

 out a potential transformer or multiplier, by connecting 

 the transformer for the lowest potential. 



When the normal voltage of both windings is above 

 5000 volts it is often more satisfactory to take core loss 



