246 



Mr. P). Hopkinson. 



[Juno 16, 



The machine was separately excited, and the no-load characteristic- 

 curve for a speed of 1500 revolutions per minute is shown on fig. 1. 



FIG. 1. 



CURRENT IN FIELD MAGNETS. 



The currents are in arbitrary units, the potential is the square root of 

 mean square of the alternating potential. The lower parts of the 

 characteristic are a good deal affected by the previous treatment of the 

 magnets ; the curve gives average values. The machine gives, at 

 no-load and at all excitations, very approximately a sine-wave of 

 E.M.F., the actual value being E (sin pt + ^ sin 3 pt + terms of 

 higher order). With a heavy non-inductive load and low field, 

 however, the field is a good deal distorted. In fig. 2 is shown the 

 curve of E.M.F. of the machine when excited with a current of 10'5 

 and working as a generator on a non-inductive resistance amounting 

 together with the armature resistance to 1'5 ohms. 



The machine was worked off the local supply mains, which gave a 

 potential of from 9498 volts x /(mean-) with a frequency of 50 per 

 second. The impressed E.M.F. is also approximately a sine-curve. 

 The resistance and reactance (Lp) of the transformer, mains to the 

 power house, &c., were determined from the drop in pressure at the 

 terminals when giving a heavy non-inductive and inductive current 

 respectively. The resistance was equivalent to about O'l ohm in the 

 motor circuit, the reactance to about 0-12 ohm. The pole-pieces of 

 the machine are laminated and cast into a solid yoke. 



The pole pieces are of 2j-inch square section, and 3J inches deep 

 from the pole face to where they are set into the yoke. The diameter 

 of the armature is 5J inches. 



