Quiz: Electrical Engineering 25 June 2020

Quiz: Electrical Engineering
Topic: DC Generator

Each question carries 1 mark.
Negative marking: 1/4 mark
Time: 10 Minute

1. Which of the following characteristics reveal about the magnetization nature of the machine?
a) No-load characteristics
b) Load characteristics
c) Armature characteristics
d) Both no-load and load characteristics

2. Choose the most inappropriate out of the following for the no-load characteristics of the dc generator.
a) It is the open circuit characteristic of the machine
b) It is magnetization characteristic of the machine
c) It is conducted on the unloaded machine
d) None of the mentioned

3. The external characteristic is plotted between
a) terminal voltage vs armature current at constant excitation
b) terminal voltage vs field current at constant armature current
c) induced armature emf vs armature current at constant excitation
d) none of the mentioned

4. Armature characteristic is also known as
a) regulation characteristic
b) magnetization characteristic
c) external characteristic
d) load characteristic

5. The air gap line represents
a) magnetic behavior of the air gap of the dc machine
b) magnetic behavior of the air gap of the induction machine
c) magnetic behavior of the iron core
d) all of the mentioned

6. For a given dc generator, the external characteristic is plotted. Without using further plots, how can we obtain internal characteristic?
a) By adding the I_a R_a drop to the plot
b) By adding armature reaction
c) By reducing I_a R_a drop
d) All of the mentioned

7. Why is armature of a dc machine made of silicon steel stampings?
a) To reduce hysteresis loss
b) To reduce eddy current loss
c) For the ease with which slots can be created
d) To achieve high permeability

8. What losses occur in the teeth of dc generator?
a) To reduce hysteresis loss
b) To reduce eddy current loss
c) To reduce eddy current as well as hysteresis losses
d) To achieve high permeability

9. For a 220-V level compound generator the terminal voltage at the half load is
a) more than 220-V
b) same as no-load voltage
c) more than no-load voltage
d) lesser than no-load voltage

10. The voltage drop in terminal voltage from no-load to full load in a shunt generator can be compensated using
a) aiding series field
b) long-shunt, differential field
c) aiding shunt field
d) any of the measures

Sol 1.
Answer: d
Both no-load as well as load characteristics are required to predict the magnetization of the machine.

Sol 2.
Answer: d
All the mentioned nature of the characteristics is correct.

Sol 3.
Answer: a
The external characteristic is plotted between terminal voltage and armature current at fixed excitation.

Sol 4.
Armature characteristic is also known as regulation characteristic. It is so called due to the fact that the difference in the terminal voltage helps to determine the voltage deviation.

Sol 5.
Answer: a
Air gap line in the magnetization curve represents the ideal nature of the machine considering no saturation for the dc machine.

Sol 6.
Answer: a
Adding the armature resistance drop we can obtain the external characteristic for a dc generator.

Sol 7.
Answer: a
The silicon steel has very high permeability and makes the flux past consistent. Thereby making lesser losses.

Sol 8.
Answer: c
Teeth of the machine has both eddy current losses as well as hysteresis losses.

Sol 9.

Answer: b
In a level compound dc generator the terminal voltage remains same as no load voltage at all the loading.

Sol 10.
Answer: a
By aiding the series field the armature reaction drop can be compensated.

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