Electrical Machines Questions and Answers – Rotating Amplifiers

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This set of Electrical Machines Multiple Choice Questions & Answers (MCQs) focuses on “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

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 favourable transient conditions
b) favourable transient conditions
c) high power gain
d) favourable steady state conditions

Explanation: The rotating amplifiers have stable transient conditions, which makes them favourable to use in high power sectors.

3. The ordinary dc machines are not favourable as amplidynes due to _________
a) sluggish transient response
b) low stability
c) poor gain
d) high steady state error

Explanation: The sluggish transient response of the ordinary dc machines makes them inappropriate to use them in amplidynes.
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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

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

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

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

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
c) feedback at all possible loads

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

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

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

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

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

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

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

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.

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