2 5 6 



PHASE CHANGERS, ETC. 



[Exp. 



shown. The delivered currents are taken from a, b, c. The 

 voltage relations are shown in Fig. 6, where a', b', c' gives the 

 maximum delivered voltage. As the rotor is turned, this becomes 

 a", b", c", etc., until the minimum a'", b'", c'" is obtained. 



' \ ^si; 



\ s I 



FIG. 5. Connections. FIG. 6. Voltage relations. 



Polyphase potential regulator: supply voltage, i, 2, 3; secondary coils, x, y, s, 

 in series with load ; delivered voltage, abc. 



With a voltmeter, show that the secondary voltages x, y and z 

 do not change in value with a change in position of the rotor; 

 also show that the three delivered voltages, ab, be, ca, are sub- 

 stantially equal for any one position of the rotor. (That x, y, z 

 do not change and ab, be, ca change simultaneously, as the rotor 

 changes, is well shown by incandescent lamps.) 



Measure one delivered voltage, as ab, for different rotor posi- 

 tions, noting particularly the positions for maximum and mini- 

 mum values, and plot a curve, as in Fig. 3. 



Construct a diagram to scale, as in Fig. 6, making the triangle 

 I, 2, 3 equal to the primary voltage; the circles have radii equal 

 to the secondary voltages, x, y and z. From this diagram pick 

 off values of delivered voltage, a'b', a"b" , etc., for different rotor 

 positions and plot these values as a second curve, to be compared 

 with the first curve already plotted from measurement. The 

 limiting values of delivered voltage are shown to be E^ 2E 2 

 cos 30. 



