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Motor & Generator Theory > DC Chapter 16 > Flashcards

DC Chapter 16 Flashcards

1
Q 
Most DC generator brushes that carry the current from the commutator to the external circuit are made of:
A) Carbon and lead 
B) Carbon 
C) Graphite and lead 
D) Copper and lead
A

B) Carbon

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2
Q

The degree that the neutral plane of a DC generator will shift under load is:
A) Inversely proportional to the load
B) Proportional to the load
C) Always less than proportional to the load
D) Independent of the load

A

B) Proportional to the load

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3
Q

DC generators are generally classified according to the manner in which:
A) They are used
B) The field windings are connected to the load
C) The armature circuit is connected to the load
D) The field windings are connected to the armature circuit

A

D) The field windings are connected to the armature circuit

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4
Q 
The effects of armature reaction in a DC generator are reduced by the use of:
A) Armature flux shift 
B) Field flux shift
C) Commutating or interpoles 
D) Exciter current increase
A

C) Commutating or interpoles

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5
Q

A shunt wound DC generator will build up to full terminal voltage with no external load connected to it due to:
A)The large conductors used in the armature
B) Motor action of the generator
C) interpoles
D) Self-excitation

A

D) Self-excitation

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6
Q 
The part of a DC generator into which the working voltage is induced is the:
A) Yoke 
B) Field poles
C) Armature 
D) Commutator
A

C) Armature

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7
Q 
A DC generator which has both shunt and series field coils is :
A) Double strength
B) Group wound 
C) Pair wound
D)Compound wound
A

D)Compound wound

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8
Q 
The field current build-up in a self-excited DC generator is dependent upon:
A) Residual magnetism
B) Applied field voltage 
C) Armature reaction
D) Field commutators
A

A) Residual magnetism

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9
Q 
A shunt most nearly means a:
A) Parallel circuit
B) Series circuit
C) Series-parallel circuit
D) Short circuit
A

A) Parallel circuit

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10
Q 
A shunt wound DC motor has a:
A) Nearly constant speed under varying loads
B) Varying speed under varying loads 
C) Varying speed under constant load
D) Constant speed under all conditions
A

A) Nearly constant speed under varying loads

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11
Q

A DC series motor is more adaptable where a:
A) Small variation of torque and speed is needed
B) Wide variation of torque but a small variation of speed is needed
C) Wide variation of torque is required & wide variations in speed are allowable
D) Constant speed is needed

A

C) Wide variation of torque is required & wide variations in speed are allowable

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12
Q 
When the load is applied to a DC shunt motor, which one of the following will happen?:
A) Speed decreases-counter EMF goes up
B) Speed increases-counter EMF goes down
C) Speed increases-counter EMF goes up
D) Speed decreases-counter EMF goes down
A

D) Speed decreases-counter EMF goes down

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13
Q 
The counter EMF of a DC motor is zero when the:
A) Motor is at rated speed
B) Armature is not turning
C) Motor is almost up to rated speed
D) Armature has just begun to turn
A

B) Armature is not turning

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14
Q 
The horsepower developed by a motor depends mainly upon which of the following two factors:
A) Speed and voltage 
B) Speed and torque 
C) Torque and voltage 
D) Torque and watts
A

B) Speed and torque

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15
Q 
A motor which has an output of 820 watts and an input of 960 watts has an efficiency of approximately:
A) 90%
B) 85%
C) 75%
D) 70%
A

B) 85%

Output / Input x 100% = effiency
(820 / 960) x 100% = 85%

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16
Q 
If the no-load speed of a shunt motor is 1800 rpm and the full-load speed is 1475 rpm, the speed regulation is:
A) 18%
B) 22%
C) 2.2%
D) 1.8%
A

B) 22%

(1800 - 1475) / 1475 x100 = 22%

17
Q 
The generated voltage (counter EMF) of a DC motor: 
A) Opposes the impressed voltage
B) Opposes any change in load
C) Aids the impressed voltage
D) Supplies current to the field
A

A) Opposes the impressed voltage

18
Q

Too much resistance inserted in the field circuit of a unloaded shunt or compound motor will:
A) Cause the motor to slow down
B) Increase back voltage
C) Allow the motor to overspeed and destroy itself
D) Not affect the motor speed

A

C) Allow the motor to overspeed and destroy itself

19
Q

The main purpose of the commutator on a DC motor is to:
A) Convert DC voltage to AC
B) Prevent the armature polarity fro automatically reversing itself as the brushes move form one segment to another
C) Automatically reverse the polarity of the field coils
D) Automatically reverse the armature polarity each time the brushes move from one segment to another

A

D) Automatically reverse the armature polarity each time the brushes move from one segment to another

20
Q 
Commutator segments are insulated from each other by: 
A) Small strips of wood 
B) A rubber insert
C) Laminated varnish 
D) Sheet mica
A

D) Sheet mica

Motor & Generator Theory (6 decks)

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