CHAPTER XIII 

 SYNCHRONOUS MOTORS AND GENERATORS 



Note. All graphical problems are to be worked on large sheets. 

 Always draw the current vectors. 



1. Two 110-volt alternators, for which co is 400, are mechanically 

 coupled and connected in series upon a circuit of 5 ohms and 0.005 

 henry. How much power will be given by each machine to the 

 circuit when the e.m.f. 's of the two machines are 30, 45 and 90 

 degrees apart? (SO min.) 



2. The same machines as in problem 1 are used in the same 

 way upon a circuit of 2 ohms resistance and 6 ohms reactance. 

 Determine the power for the same phase angles. (30 min.) 



3. Two alternators each generate 2000 volts; each has the arma- 

 ture resistance, 2, the inductance, 0.07, and the frequency, 60. 

 They are run in parallel and owing to throttling of one engine a 

 phase displacement (from opposition) of 30 degrees results. How 

 many kilowatts are being supplied by the motor action of the 

 synchronizing current and how much copper loss results? Solve 

 graphically. (25 min.) 



4. A synchronous motor, running on a 2000-volt line, is over- 

 excited so that with 10-amperes load its current leads the e.m.f. 

 30 degrees. A choke coil with 20-ohms reactance and J-ohm 

 resistance is placed in series with it; what is the e.m.f. at the motor 

 terminals? (3 min.) 



5. A synchronous motor is run on a 440-volt, 60-period circuit 

 and takes 20 amperes leading 30 degrees. If an induction coil with 

 L, 0.01, is in series with it, what will then be the e.m.f. on the 

 motor? (3 min.) 



6. A synchronous motor running on a 1200-volt system has 

 an armature resistance of 1.2 and reactance of 5.8 ohms. For a 

 certain field current, the motor gives 1100 volts counter e.m.f. 

 (neglect the change in this due to armature reactions). Construct 

 the parallelogram diagrams for currents of 10, 25 and 40 amperes. 

 Let the line e.m.f. vector be common to all three diagrams. 



