
Problem 
Answer 
1 
Construct accurately the circle diagram for Example 182. Calculate the torque and the power output at onehalf of rated speed. Calculate the starting torque with 200 volts applied (linetoline). 

2 
At what continuous power output may a 50hp, 3phase, 60cycle, 220volt , polyphase, opentype, 40deg C induction motor be operated if it be totally enclosed and connected to a singlephase, 208volt, 50cycle line? 

3 
The fullload speed of an induction motor is given as 960 rpm. What is the frequency for which it was probably designed? If the windings are open for inspection, how may the number of poles be determined? 

4 
A 3phase, 220volt, 6pole, 25hp, 25cycle induction motor has a power input of 575 watts with 19.5 amp at no load. With the rotor blocked and 51.5 volts applied to the stator, the power input is 2050 watts with a line current of 66 amp. The effective resistance of the motor is 0.085 ohm per phase. Draw the approximate circle diagram, and determine the starting torque and the maximum running torque in poundfeet. 

5 
A 3phase, 4pole, 60cycle, 220volt, polyphase induction motor is to be used as a frequency converter by driving the opencircuited rotor backward against the direction of the rotating field. If the rotor has half as many conductors in series per phase as the stator, what will be the voltage and frequency available at the sliprings when the rotor is driven backward at 900 rpm? 

6 
A 6pole, 50hp, 25cycle induction motor runs at 5% slip at full load. What is the frequency of the rotor currents? 

7 
At full load, what is the speed of the motor of Problem 6? 

8 
A 40hp, 440volt, 1200rpm induction motor with 5% slip at full load has a starting torque 1.5 times its fullload running torque. How many poundfeet of starting torque would it develop with 230 volts applied? 

9 
How many poundfeet of starting torque would the 40hp motor of Problem 8 develop if started on the 80% tap of its starting autotransformer? 

10 
When tested for the purpose of finding the characteristics by circle diagram, a certain twophase induction motor yields the following data:
Phase 1 Phase 2
Volts Amp Watts Volts Amp Watts Speed
No load 440 5.5 440 440 5.5 440 1800 rpm
Blocked 113 11.4 575 113 11.4 575 0
Resistance = 1.56 ohms per phase.
Draw the circle diagram and calculate:
 Starting torque, in poundfeet, considering starting torque as 1.5 times fullload torque.
 Torque at half of rated speed.
 Efficiency at 1.5 times fullload hp.

