62 ELECTRICAL ENGINEERING PROBLEMS 



25. A 7-ampere series-arc lighting system is operated upon a 

 8600-volt circuit. The volts per lamp are 75 and the power factor 

 of the lamps is 83%. The current is maintained constant by a 

 75-light inductive regulator having 30 ohms resistance. What 

 will be the voltage across its terminals when the full load of lamps 

 is on; also for 40 lights, and for 5 lights? (10 min.) 



26. Construct the diagram for a rotary converter, reactance 

 coil and line in series. The converter is taking 120 amperes, 

 lagging 30 degrees, and its terminal e.m.f. is 1000 volts. The 

 resistances of the coil and line are 0.4 and 0.8 ohms, and their 

 reactances 1.5 and 0.2 ohms. Find the generator e.m.f., the power 

 factor of the system and the voltage at the end of the line. (6 

 min.) 



27. Find graphically the sum of the following currents and 

 the tangent of the lag of the resultant: 



30 amperes, lagging 15 degrees, 

 20 amperes, lagging 45 degrees, 

 10 amperes, leading 30 degrees, 

 5 amperes, in phase. (4 min.) 



28. An induction motor taking 50 amperes and with a power 

 factor of 0.7 has in parallel with it 200 J-ampere lamps in parallel. 

 Find the total current. (3 min.) 



29. At a certain point in a circuit there are 50 amperes flowing 

 with a power factor of 86.6%. 20 amperes is then taken off for 

 a group of incandescent lamps while the balance passes on to an 

 induction motor. What current does the motor take and at what 

 power factor? (3 min.) 



30. Two parallel circuits on a 2200- volt system have resistances 

 of 5 and 10 and reactances of 5 and 20; required the current and 

 lag. (7 min.) 



31. Fifteen 50-watt, 100-volt lamps are in parallel on a 100- 

 volt system and in parallel with a circuit of 5 ohms and 0.005 

 henry; the frequency is 120. What is the current, the angle of 

 lag and the power factor? (8 min.) 



32. Ten enclosed arc lamps in parallel, each taking 6 amperes 

 and 70 volts active e.m.f., and with choke coils in series, are 

 in parallel with 250, 110-volt, 0.55-ampere incandescent lamps. 

 What will be the total current? (6 min.) 



