66 Chapter 4 • Alternating current motors


Exercise 4.3


1. What method of connection is used for the stator of a three-phase induction motor?


2. When is a star-connection used for the stator of a three-phase motor?


3. Is a single-phase induction motor self starting? Give a reason for your answer.


4. What is done to enable a single-phase induction motor to start? 5. What are capacitors used for with single-phase induction motors? 6. Draw a circuit diagram of a capacitor-start, induction run motor.


7. Does the capacitor of a capacitor-start, induction run motor remain in the circuit? Give a reason for your answer.


8. What is the main difference between a capacitor-start, induction run, and a capacitor-start, capacitor-run, single-phase induction motor?


9. Draw a circuit diagram for a capacitor-start, capacitor-run motor.


10. What is the advantage of leaving a capacitor in the circuit of the auxiliary winding of a single-phase induction motor while it is running?


11. What is meant by a universal motor and why is it named as such?


12. What is the constructional difference between the cores of the field windings of a dc series motor and those of an ac series motor?


13. What does SANS 10142 stipulate with regard to single-phase protection for three-phase motors?


14. What does SANS 10142 stipulate with regard to overcurrent protection of a motor circuit?


15. What does SANS 10142 stipulate with regard to time delay and overcurrent protection of motors?


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