CHAPTER III 



CORE LOSS TESTS, OPEN-CIRCUIT, 

 SHORT-CIRCUIT, DECELERATION 



Three methods are used to measure the core losses 

 on rotating direct current apparatus and alternating 

 synchronous apparatus. They are known as follows: 

 "running light core loss," "belted core loss," and 

 "deceleration core loss." The "running light" test 

 is made on all direct current generators and motors 

 which are given a running test. It is occasionally, 

 though not frequently, employed with alternating cur- 

 rent synchronous apparatus. 



The following conditions must obtain with direct 

 current apparatus in order to give satisfactory results: 

 Brushes must be shifted on the commutator to the 

 no-load neutral point; the spring tension must be 

 normal, and the commutator clean, so that the normal 

 operating commutator and brush friction values are 

 obtained. This test, wherever possible, should be made 

 after all the others have been finished, in order to have 

 a glossy commutator, with its surface in good operating 

 condition. The driving power should be supplied from 

 a variable voltage circuit that is not subject to sudden 

 fluctuation. Since the power input required to drive 

 the machine running free as a motor must be obtained, 

 its value must not be read when the rotating parts 

 are either accelerating or decelerating. A steady volt- 

 age must be kept on the armature and the field current 

 must have a constant value. 



When "running light" tests are made on direct 

 current generators, the observations must be made with 

 full load field flux. The potential applied to the arma- 

 ture must be equal to the normal rated voltage of the 

 generator, increased by the CR drop in the armature 



[19] 



