7 - 19 Flashcards
Commutator segments are insulated from each other by?
A) small strips of wood
B) a rubber insert
C) laminated varnish
D) Sheet mica
D) Sheet mica
pg 15
Most DC generator brushes that carry the current from the commutator to the external circuit are made of?
A) Carbon and lead
B) Carbon and graphite
C) Graphite and lead
D) Copper and lead
B) Carbon and graphite
pg 17
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 to the load
B) Proportional to the load
pg 10
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
D) The field windings are connected to the armature circuit
pg 1
The effects of armature reaction in a DC generator are reduced by the use of?
A) Commutating windings
B) Commutating windings and interpoles
C) Commutating or interpoles
D) Exciter current
C) Commutating or interpoles
pg 10
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
D) Self-excitation
pg 7
The part of a DC generator into which the working voltage in induced is the:
A) Yoke
B) Field Poles
C) Armature
D) Commutator
C) Armature
pg 1
The field coil windings of a self-excited DC generator are:
A) Series
B) Shunt
C) Compound
D) Any one of the Above
D) any one of the above
pg 7
The rated voltage value of a DC generator will be reached faster if the generator is:
A) Seperately excited
B) Self-excited
C) Brought up to speed rapidly
D) None are correct
B) Self-excited
pg 7
A shunt most nearly means a:
A) Parallel circuit
B) Series circuit
C) Series and Parallel circuit
D) Any of the above
A) Parallel circuit
pg 7
Which of the following is true regarding the speed regulation of a shunt motor?
A) It has a constant speed characteristic under varying loads
B) It has a varying speed characteristic under varying loads
C) It has a varying speed characteristic under constant loads
D) none of the above are correct
A) It has a constant speed characteristic under varying loads
pg 21
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 and wide variations in speed are allowable
D) Constant speed is needed
C) Wide variation of torque is required and wide variations in speed are allowable
pg 21
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
D) Speed decreases, counter EMF goes down
pg 19
The counter EMF of a DC motor is zero when the:
A) Moter is at rated speed
B) Armature is not turning
C) Motor is almost up to rated speed
D) Armature has just begun to turn
B) Armature is not turning
pg 20
The horsepower developed by a motor depends mainly upon which of the following 2 factors?
A) Speed and voltage
B) Speed and torque
C) Torque and voltage
D) Torque and watts
B) Speed and torque
pg 20
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%
B) 85%
Efficency=output/input
E=820/960
E=.85 or 85%
pg 24
If the no-load speed of a shunt motor is 1800 rpm and the full load speed is 1475 rpm, the sped regulation is:
A) 18%
B) 22%
C) 2.2%
D) 1.8%
B) 22%
Speed Regulation=no load speed-full load speed/full load speed
S=(1800-1475)/1475
S=.22 or 22%
pg 26
The generated voltage(counter EMF) of a motor:
A) Opposes the impressed voltage
B) Opposes any change in load
C) Aids the impressed voltage
D) none of the above is correct
A) Opposes the impressed voltage
pg 19
Too much resistance inserted in the field circuit of a shunt or compound motor will:
A) Cause the motor to slow down
B) Increase back voltage
C) Allow the motor to over speed and destroy itself
D) Not affect the motor speed
C) Allow the motor to over speed and destroy itself
pg 21
The main purpose of the commutator on a DC motor is to:
A) Convert DC voltage to AC
B) Prevent the armature polarity from automatically reversing as the brushes move from 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.
D) Automatically reverse the armature polarity each time the brushes move from one segment to another.
pg 19
