Problems
Author: E.E. Kimberly

Problem 
Answer 
1 
What is the fullload current per terminal of a 2300volt, 3phase, 2000kva alternator? 

2 
A 2300volt, Yconnected, 100amp, 0.8PF alternator has internal impedance of 1 +j5 ohms per phase. A full load of 100% PF is being supplied at the rated terminal voltage. If the load is removed, but the fieldrheostat setting is kept the same, what will be the terminal voltage? If, then, a full load with 70% PF leading is applied, what will be the terminal voltage? Assume the internal impedance to remain constant. 

3 
A 40,000kva, 13,200volt, 3phase, 60cycle, Yconnected alternator has a stray power loss equal to 1.5% and a field loss equal to 0.4% of the rated output kva at 85% power factor lagging. The effective stator resistance is 0,10 ohm per phase. Calculate the efficiency at full load of 85% power factor, lagging. 

4 
A 50kva, Yconnected, 3phase, 220volt, 1200rpm, 0.8power factor, 60cycle alternator requires 2.5 hp to drive it at rated speed at no load with field excitation. The stator resistance is 0.05 ohm per phase. The fieldcircuit power input at full load is 2 kw. Calculate the efficiency at full load of 80% power factor lagging. 

5 
Two similar 3phase, 2000kva alternators in parallel supply a 3500kw load of 80% power factor lagging. If the output of the first alternator is 1600 kw at 70% power factor, what are the kw and kva outputs of the other? 

6 
A 96pole alternator is to be used to supply a 50cycle power system. At what speed must it be run? 

7 
An alternator running at 375 rpm generates 25 cycles per second. How many poles does it have? 

8 
The stator of a 1000kva alternator designed to be driven by a steam engine is much larger and shorter than one of the same electrical size designed for direct connection to a steam turbine. Explain. 

