54 PROBLEMS IN ALTERNATING CURRENT MACHINERY 



field structure has 64 poles each of which is wound with 50 turns. 

 The resistance of the field circuit is 0.516 ohm. The armature 

 core has 384 slots with 3 inductors in series per slot. Each in- 

 ductor is 10 in. long. The hot resistance of the armature meas- 

 ured between terminals is 0.264 ohm. The ratio of effective 

 to ohmic resistance is 1.3. In calculating the leakage reactance 

 assume 6.5 lines per ampere per inch of inductor. The armature 

 windings are connected in Y. The open- and short-circuit 

 characteristics are given by the following data : 



The rotational losses at normal voltage are 17.2 kw. 



This motor deliveres 1000 h.p. and the excitation greater than 

 normal and is adjusted so that it is operating from a 2200-volt 

 circuit at a power factor of 0.93. 



(a) Calculate the voltage impressed on the field circuit Use 

 the general method. 



(b) Calculate the voltage impressed on the field circuit. Use 

 the synchronous-impedance method. 



(c) Calculate the voltage impressed on the field circuit. Use 

 the magnetomotive-force method. 



6. A 2-phase, 10,000-volt synchronous motor is rated to deliver 

 4500 h.p. when operating at unit power factor. The armature 

 has an effective resistance of 0.64 ohm per phase. The open- 

 and short-circuit characteristics are given by the following data: 



This motor is delivering 3760 h.p. with an efficiency, exclusive 

 of field loss, of 95.6 per cent., and the field current is adjusted 

 so that it takes a leading current at 0.91 power factor. 



