Electrical 2 - chapter 4

1. The sole purpose of a commutator in a dc generator is to

• a. increase output voltage
• reduce sparking at brushes
• provide smoother output
• convert the induced ac into dc

2. The series field of a short shunt dc generator is excited by ________ currents

• shunt
• armature
• load
• external

3. In a d.c. generator, the generated emf is directly proportional to the

• number of dummy coils
• number of poles
• number of armature parallel paths
• all of the above

4. The commercial efficiency of a shunt generator is maximum when its variable loss equals ______ loss

• constant
• iron
• friction and windage
• none of the above

. The external characteristic of a dc generator is the curve between

• V and IL
• E and Ia
• E0 and Vf
• V and If

6. The internal characteristic of a dc generator is the curve between

• V and Ia
• E and Ia
• E0 and Vf
• V and If

7. The open circuit characteristics of a dc generator is the curve between

• V and Ia
• E and Ia
• E0 and If
• V and If

8. Which of the following dc generator cannot build up on open circuit?

• shunt
• . series
• . short shunt
• long shunt

9. Fleming’s right hand rule is applicable to

• dc generator
• dc motor
• transformer
• all of the above

10. The nature of current flowing in the armature of a dc generator is

• ac
• dc
• . pulsating
• . dc superimposed over ac