ROTARY CONVERTERS 103 



two machines. Any slight pulsation will be shown 

 by these instruments at once. The direct current 

 volts should be held constant on one machine throughout 

 the test. Now, with the field current on one machine 

 held at minimum input value, the field current on the 

 other machine should be reduced to about one-half 

 minimum input value. If no pulsation is noted, a full 

 set of readings should be taken on both machines, 

 reducing the field current of the other machine to 

 one-half minimum input value and watching for pul- 

 sation on both machines, which now take a heavy 

 lagging current. A full set of readings under these 

 conditions should be taken. The field of the first machine 

 is again adjusted to the minimum input value, readings 

 are taken, and pulsations watched for. With this field 

 held at minimum input, the field of the other machine 

 should be changed from its value of one-half minimum 

 input to twice the minimum input value, readings and 

 observations being made as before. The other field 

 should then be brought up to twice normal value 

 readings taken, and the effect of the heavy leading 

 current in each machine noted. Leaving one field 

 over-excited, the other field should be weakened to 

 give minimum input, and a full set of readings taken. 

 If no pulsation develops with the high line drop under 

 these extreme conditions, the machines are satisfactory. 



Input-Output Efficiency Test 



Input-output tests on small machines (300 kw. or 

 less) are made with the machine running as a rotary, 

 dead loaded on a water-rheostat. Larger machines 

 are tested in pairs, one machine pumping back on the 

 other with an electrical loss supply. The machines 

 are wired in a manner exactly similar to that used 

 in a pump back heat run (circulating power heat test), 

 special attention being given to the wiring to see that 

 no unbalancing occurs on either the alternating current 

 or the direct current circuits. With the machine running 

 as a rotary, wattmeters are connected in the alternating 

 current end, between the rotary and transformers, and 

 preparations made for reading direct current armature 



