SYNCHRONOUS MOTORS 63 



226 amperes at a terminal potential difference of 2180 volts and 

 delivers 812 h.p. The no-load rotational losses are 23 h.p., and 

 may be assumed constant. The. armature windings, which are 

 Y-connected, have an effective resistance of 0.172 ohm and a 

 synchronous reactance of 2. 1 2 ohms per phase. 



At what power factor is the motor operating? Neglecting the 

 field copper losses, what is the efficiency? 



35. At no load a 3-phase sj r nchronous motor takes line currents 

 of 1.52 amperes at 11,000 volts if the field current is adjusted for 

 a minimum armature current. The armature windings, which 

 are connected in Y, have an effective resistance of 0.94 ohm and 

 a synchronous reactance of 56 ohms. 



When the motor receives 960 kw. at 11,000 volts and the 

 excitation is adjusted so that the line current is 72 amperes, what 

 is the output? If the excitation is greater than normal, what is 

 the excitation voltage? 



36. The no-load rotational losses of a 1340-h.p., 3-phase syn- 

 chronous motor are 34.6 kw. The armature windings are con- 

 nected in Y and have an effective resistance of 0.067 ohm and a 

 synchronous reactance of 2.64 ohms per phase. This motor is 

 operated from a 2400-volt circuit and when delivering its rated 

 output the excitation is adjusted so that the motor takes a leading 

 current of 0.83 power factor. 



What is the power input? What is the excitation voltage? 



37. At no load a 150-h.p., 2-phase synchronous motor takes 

 7.6 kw. at 480 volts when the excita tion is adjusted for a mini in u in 

 armature current. Under load this motor takes 108 amperes at 

 485 volts when the excitation is adjusted so that the power factor 

 is 0.78. The effective resistance of the armature is 0.118 ohm 

 and the synchronous reactance is 2.13 ohms. 



What is the output? What is the excitation voltage (a) if 

 the field current is greater than normal? (b) if the field curn-nt 

 is less than normal? 



38. A :*-j>hase, 6600-volt synchronous motor is operated at 

 its rated voltage and delivers its rated output of 6500 h.p. 

 In order that the motor shall take a large leading cum-nt tin- 

 field current is adjusted for an excitation voltage of 8100 \<lt<. 

 The no-load rotational losses are 138 kw. and may be assumed 

 constant. The armatun windings are conn < tr.l in Y and have 

 an effective resistance of 0.081 ohm .UK I a synchronous reactance 

 of 2.8 ohms. 



