SYNCHRONOUS MOTORS 65 



per phase. The rotational losses at normal voltage are 57 h.p. 

 and may be assumed to be constant. 



At what per cent, of its rated capacity must the synchronous 

 motor be operated so that the power factor of the entire load shall 

 be unity and the line voltage 13,200 volts? Calculate the n 

 sary field current of the motor for this condition by the magneto- 

 motive-force method. 



43. A 1000-h.p. synchronous motor is operating at the end 

 of a 3-phase transmission line which has a resistance of 0.58 ohm 

 and a reactance of 0.64 ohm per conductor. The motor is over- 

 excited so that it takes a line current of 216 amperes at a power 

 factor of 0.82, and with a line potential difference of 2210 volts. 



What is the line voltage at the generating station? What is 

 the efficiency of transmission? 



44. A synchronous motor operating at the end of a 3-phase 

 transmission line takes a constant power of 1500 kw. The 

 resistance and reactance of the line are respectively 2.2 ohms and 

 2.6 ohms per conductor. The line voltage at the generating 

 station is maintained at 5740 volts. The excitation of the 

 motor is adjusted so that the line loss has its least possible value. 



What is the terminal voltage at the motor? What is the 

 efficiency of tnin>mi ion ? 



45. A synchronous motor operating at the end of a 3-phase 

 transmission line which has a resistance of 3.6 ohm and a re- 

 actance of 4.1 ohm per conductor takes a constant po\\- 

 720 kw. from the line and the excitation is adjusted so that the 

 line voltage is 5000 volts. Ih lin voltage at the gnu-nit ing 

 station is also maintained at 5000 volts. 



(a) What current does the motor take? At what p< 

 factor is it operating ? 



(b) If the motor is Y-connected and has an effective resist- 

 ance of 0.40 ohm and a synchronous reactance of 15.4 ohms per 

 phase, what is the necessary excitation voltage? 



