124 PROBLEMS IN ALTERNATING CURRENT MACHINERY 



power factor. The synchronous motor takes a constant load of 

 460 kw., and, with the greatest allowable field excitation, its line 

 current is 610 amperes and the terminal voltage is boosted to 

 650 volts. 



Calculate the terminal voltage of the generator's exciter and 

 the combined efficiency of the generator, line and transformers. 



Use what you consider the most exact method. 



72. A constant induction motor load taking 2500 kw. at 

 0.91 power factor and with a line voltage of 13,200 volts is at 

 the end of a short transmission line. For this load the efficiency 

 of transmission is 91.3 per cent, and the voltage regulation of the 

 line is 11.2 per cent. Asynchronous motor of suitable capacity 

 is added at the load so that when running light with full-load 

 current the resultant power factor at the load is increased to 

 unity. Assume that the efficiency of this synchronous motor 

 at full load and unit power factor is 0.93. The voltage at the 

 load is maintained constant. 



What is the necessary capacity of the synchronous motor? 

 What are the efficiency of transmission and the voltage regula- 

 tion of the line after the synchronous motor is added? 



73. An induction motor load at the end of a three-phase 25-cycle 

 transmission line takes 7600 kw. at 0.912 power factor and 

 with a line voltage of 11,000 volts. The resistance and induc- 

 tance of the line are respectively 1.4 ohms and 6.5 millihenrys per 

 conductor. A synchronous motor, running light and taking 

 full-load current, is added at the generating station to improve 

 the power factor and thus increase the capacity of the line at the 

 load. Assume that the full-load efficiency of this motor is 94 

 per cent, when operating at unit power factor. The voltage 

 at the load is maintained constant. Induction motors, operating 

 at the same power factor as do the others, are added at the load 

 and the synchronous motor is adjusted so that the generating 

 station operates at unit power factor. For the same line cur- 

 rent in the station as was required before the addition of the 

 synchronous motor calculate the permissible increase in the 

 induction motor load. What is the kilovolt-ampere capacity of 

 the necessary synchronous motor? What is the line voltage at 

 the generating station before and after the synchronous motor 

 is added? 



74. An induction motor load taking 5400 kw. at 0.914 power 

 factor and with a line voltage of 13,200 volts is at the end of a 



