26 



COMMERCIAL ELECTRICAL TESTING 



It is often necessary to determine the core loss, friction 

 and windage losses of large machines when it is im- 

 practicable to employ the belted core loss method. 

 The running light reading alone does not allow the 

 separation of the core loss from friction and windage. 

 A method known as the deceleration core loss is used 

 for this purpose. Such tests are employed regularly 

 on turbine-driven units, and it is often very convenient 

 to use them in connection with certain vertical water- 



80 

 70 

 60 



^40 



^30 



20 



10 



"800 JZOO /600 2000 2400 



Vo/ts /Ir/ji&tc/re 



Fig. 9. Open Circuit Core Loss Curve taken from Deceleration 

 Curves of Fig. 8 



wheel-driven generators and other exceptionally large 

 horizontal alternators and direct current machines 

 possessing a considerable flywheel capacity. 



A running light reading at normal speed and normal 

 voltage should be taken to give the driving power 

 necessary under that condition. Where this is not 

 practicable, the moment of inertia of the rotating part 

 must be known. This can be very accurately calculated 

 for the majority of machines from their mechanical 

 dimensions, as given by the working drawings. The 

 test is as follows: First drive the machine with full 



