THE ROTARY CONVERTER. 



current machine terminals to a variable load resistance in 

 series with an ammeter and switch. 



First excite the field windings, then run up to speed 

 and synchronise the rotary converter with the alternating 

 supply, and then switch the armature direct on to the 

 circuit, having previously adjusted the excitation, so that 

 the voltage is the same as that of the supply. Usually 

 the most convenient method of running the machine up 

 to speed will be to use the D. C. side as a motor and 

 to drive from a source of direct current. In order to 

 do this, break the load circuit, shown on the left of 

 the diagram, Fig. 165, and join the two free ends 

 of the circuit thus obtained to the direct-current supply. 

 On closing the switch S 2 ,'the variable resistance R^ may 

 be made to serve the purpose of a starting resistance, and 

 the speed of the machine may be regulated by varying 

 this and the field-regulating resistance. If the direct and 

 alternating supply voltages are not of suitable values, 

 difficult3 r may be experienced in getting both speed and 

 voltage on the alternating side to the correct value for 

 synchronising. In such cases it is often best to run the 

 motor up to a speed which is considerably above syn- 

 chronism, then switch off the direct-current supply and 

 switch on to the alternating circuit when the motor has 

 slowed down to the correct speed. In this case exact 

 voltage on switching in will usually not be of importance. 



After synchronising, cut out the connection to the 

 D. C. supply, then adjust the excitation until the motor 

 takes the minimum current, and complete the direct- 

 current load circuit. . 



First for no load, and then for a succession of increasing 

 loads, take readings of the alternating and continuous 

 currents and voltages, and also the power supplied as 

 registered by the wattmeter. The speed should also be 

 observed ; it should, of course, be constant. 



The results should be entered in tabular form, the 

 power factor being calculated for each set of readings by 

 dividing the watts supplied by the volt-amperes. 



Several sets of readings should be taken, first one or 

 two sets each with constant excitation, and then a set with 

 the excitation varied to give the minimum current on the 

 A.C. side. 



