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COMMERCIAL ELECTRICAL TESTING 



The driving motor must be wired so that readings 

 may be taken of amperes armature, amperes field, and 

 speed. A reading should be taken on the motor cor- 

 responding to normal speed of the machine under test. 

 The machine under test should be wired with its field 

 separately excited and provision made for reading 

 amperes field, volts field, and volts armature. Careful 

 resistance measurements of the armature of the driving 

 motor must be made previous to starting the test. 



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4 

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Fig. 6. Open Circuit Core Loss on a 500 Kw., 600 Volt, 20-Pole, 360 R.P.M. 

 3-Phase, 60 Cycle, A-C. Generator 



The test is then carried out as follows: The field of 

 the driving motor is adjusted to about normal value 

 and excited from a source of constant voltage, so that 

 its value may be held constant throughout the test. 

 The speed of the driving motor is regulated by varying 

 the voltage applied to its armature terminals. First 

 run the driving motor and the machine under test a 

 sufficient length of time to allow the friction to reach 

 a constant value. This will obtain when the input on 

 the driving motor becomes constant while driving the 

 machine under test without any field excitation. Care- 

 ful readings should then be taken, first of the input to 

 the driving motor with the machine under test unexcited 

 and all brushes down on the commutator; and second, 

 with all brushes raised from the commutator of the 



