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Operating Characteristics of DC Generators
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
Answer: d
Explanation: Both no-load and load characteristics are required to predict the magnetization of the machine.
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
Answer: d
Explanation: All the mentioned nature of the characteristics are correct.
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
Answer: a
Explanation: The external characteristic is plotted between terminal voltage and armature current at fixed excitation.
4. A student forgot to mark the x-y axes in his experiments but he just noted down the cause and the effect for each. How will he conclude about the armature characteristic out of the all plotted graphs?
a) By marking graph for constant terminal voltage
b) By marking graph for constant field current
c) By marking graph for constant armature current
d) By marking graph for constant speed
Answer: a
Explanation: Armature characteristic is observed at constant terminal voltage for emf vs armature current.
5. Armature characteristic is also known as _________
a) regulation characteristic
b) magnetization characteristic
c) external characteristic
d) load characteristic
Answer: a
Explanation: 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.
6. The air gap line represents _________
a) magnetic behaviour of the air gap of the dc machine
b) magnetic behaviour of the air gap of the induction machine
c) magnetic behaviour of the iron core
d) all of the mentioned
Answer: a
Explanation: Air gap line in the magnetization curve represents the ideal nature of the machine considering no saturation for the dc machine.
7. Identify the armature characteristic of the dc generator.
a) 
b) 
c) 
d) 
Answer: a
Explanation: At low values of the armature conductor, the increase in the field current is very small to provide IaRa drop. At large armature current,field current increases sharply to compensate for the voltage drop caused by armature reaction.
8. For a given dc generator, the external characteristic is plotted. Without using further plots, how can we obtain internal characteristic?
a) By adding the IaRa drop to the plot
b) By adding armature reaction
c) By reducing IaRa drop
d) All of the mentioned
Answer: a
Explanation: Adding the armature resistance drop we can obtain the external characteristic for a dc generator.
9. Identify the machines by observing their external characteristics for (i) and (ii) respectively.
(i) 
(ii) 
a) Separately excited dc generator, shunt generator
b) Shunt generator, separately excited dc generator
c) Differentially compound dc generator, separately excited
d) Series dc generator, shunt generator
Answer: a
Explanation: In dc shunt generator, voltage drops off much more rapidly with load due to fal in field current with terminal 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
Answer: a
Explanation: By aiding the series field the armature reaction drop can be compensated.
11. Mark the correct order for the external characteristics of compound generators from the below graph.
a) 1: over compound, 2: level compound, 3: under compound, 4: differential compound
b) 1: under compound, 2: level compound, 3: over compound, 4: differential compound
c) 1: differential compound, 2: level compound, 3: under compound, 4: over compound
d) 1: over compound, 2: differential compound, 3: under compound, 4: level compound
Answer: a
Explanation: Over compounding provides maximum voltage difference at no load while the differential compunding has least.
12. The external characteristic for the dc series generator is?
a) 
b) 
c) 
d) 
Answer: a
Explanation: There is a linear behaviour till the saturation.
13. 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
Answer: a
Explanation: The silicon steel has very high permeability and makes the flux past consistent. Thereby making lesser losses.
14. 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
Answer: c
Explanation: Teeth of the machine has both eddy current losses as well as hysteresis losses.
15. 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
Answer: b
Explanation: In a level compound dc generator the terminal voltage remains same as no load voltage at all the loading.
Rotating Amplifiers
1. The rotating amplifiers are widely used in ____________
a) small amplified outputs
b) large amplified outputs
c) amplified outputs
d) large power gain outputs
Answer: b
Explanation: The rotating amplifiers are applicable in feedback systems giving large amplified outputs.
2. The quantity which make rotating amplifier applicable in large power levels is/are _________
a) high power gain and favorable transient conditions
b) favorable transient conditions
c) high power gain
d) favorable steady state conditions
Answer: a
Explanation: The rotating amplifiers have stable transient conditions, which makes them favorable to use in high power sectors.
3. The ordinary dc machines are not favorable as amplidynes due to _________
a) sluggish transient response
b) low stability
c) poor gain
d) high steady state error
Answer: a
Explanation: The sluggish transient response of the ordinary dc machines makes them inappropriate to use them in amplidynes.
4. In rotating amplifiers, armature reaction mmf of the first stage is made to act as field flux for second stage.
a) True
b) False
Answer: a
Explanation: Yes, the reaction mmf of the first stage is made to act as field flux for second stage to have faster transient response.
5. The cross field machines have _________
a) two fluxes electrically in quadrature
b) two fluxes mechanically in quadrature
c) one set of brushes per pole
d) all of the mentioned
Answer: a
Explanation: The cross field machines have two fluxes electrically in quadrature.
6. In cross field rotating amplifiers, there is _________
a) two stage of flux generators
b) three stage of flux generators
c) four stage of flux generators
d) eight stage of flux generators
Answer: a
Explanation: There are two stages for flux generators in order to have faster response in the system.
7. Metadyne is _________ feedback with respect to main ___________
a) negative, current
b) negative, voltage
c) positive, current
d) positive, voltage
Answer: a
Explanation: Metadyne is negative feedback with respect to main current flowing in the second stage set of motors.
8. An amplidyne, d-axis flux is always neutralized due to _________
a) compensating winding at all possible loads
b) interpoles at all specified loading
c) feedback at all possible loads
d) feedback at fixed loading
Answer: a
Explanation: The d-flux is neutralized by compensating winding at all possible loads as the same flux will be produced but in the opposite direction so as to cancel the flux.
9. In amplidynes, the resultant d-axis flux is _________
a) field flux
b) difference of field flux and main flux
c) sum of field flux and main flux
d) cross magnetizing flux
Answer: a
Explanation: The resultant d-axis flux lies along the main field poles and are so field flux. The d- axis is completely under the control of field winding and is unaffected by direct axis current.
10. Amplidynes are best applicable in _________
a) feedback control systems with regulated power supply.
b) power supply
c) speed control of large motors
d) All of the mentioned
Answer: a
Explanation: Amplidynes find applications in feedback systems with large power handling requirements.
11. Interpoles provide mmf more than armature mmf in a dc machine.
a) True
b) False
Answer: a
Explanation: Interpoles nullify armature cross magnetizing flux and the reactance voltage. So it is more than the armature mmf for a good efficient machine.
12. The delay of the commutation occurs due base cause of emf induced due to _________
a) self inductance, mutual inductance
b) self inductance
c) mutual inductance
d) leakage inductance
Answer: a
Explanation: The commutation in dc machines is delayed because of the emf induced in the coils and the mutual interaction of the field with neighbour coils.
13. In the following applications of the dc machines, but all are not matched correctly. Choose the wrong marking.
I. DC shunt motor – variable speed application
II. DC compound generator – constant supply voltage
III. Differentially compounded motor – welding purposes
a) III
b) II
c) I, III
d) III, II
Answer: a
Explanation: Differentially compounded generators are used for welding purposes, not motors.
14. In the following applications of the dc machines, but all are not matched correctly. Choose the wrong marking.
I. DC shunt motor – Lathe machine
II. DC compound generator – Drilling machine
III. Differentially compounded generator – welding purposes
a) II
b) III
c) I, III
d) III, II
Answer: a
Explanation: DC compound generators are used for maintaining constant voltage across the terminals.
15. Mark the order for the decreasing order of the voltage regulation for dc generators.
a) DC shunt generator > level compound generator > Differential compound generator
b) DC shunt generator < level compound generator < Differential compound generator
c) Level compound generator > DC shunt generator > Differential compound generator
d) Level compound generator < DC shunt generator < Differential compound generator
Answer: a
Explanation: Dc shunt motor is almost constant speed generator and thus its voltage regulation is very good than all and differential compound generator has most poor v.r.