ROTARY CONVERTERS 101 



field excitation is varied through nearly as possible the 

 same range as for no load characteristic. The readings 

 taken are, for the alternating current side, volts and 

 amperes; and for the direct current side, volts armature 

 (held constant), amperes output (held constant), volts 

 field, and amperes field. The speed is held constant. 



Compounding Test with Reactance 



When a rotary is required to automatically deliver 

 a constant direct current voltage under a load subject 

 to sudden changes, a compound wound machine is 

 used with a definite reactance inserted between the 

 rotary and the line. Such reactances must be tested 

 with the machines for which they are designed. A 

 constant voltage is possible, since an alternating cur- 

 rent passing through a reactance will increase the 

 potential if leading, and decrease it if lagging. By 

 adjusting the shunt field so that about 20 per cent 

 lagging current flows at no load, the strength of the 

 series field can be adjusted to give a slightly leading 

 current at full load and thus maintain a constant direct 

 current voltage. A compound converter operating 

 with reactance in circuit must be compounded like a 

 direct current generator. Unless otherwise specified, 

 the voltage of the alternator driving the rotary should 

 be held constant and the shunt field adjusted to give 

 the correct no load voltage; when, without touching 

 the field rheostats, full load should be applied and the 

 direct current volts read. If the machine over-com- 

 pounds, the series field is too strong and gives too large 

 a leading current, in which case a shunt must be adjusted 

 across the terminals of the series winding to shunt a 

 portion of the current. In this compounding test all 

 readings are taken and all adjustments made without 

 touching the field rheostat after the no load adjustment 

 is effected, as in the case of a direct current generator. 



Pulsation Bridges 



Since the torque of a rotary only needs to be great 

 enough to overcome the mechanical losses, the machine 

 is very sensitive to changes in line conditions; i.e., 



