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Dc Machines Basic
Which of the following DC motor has the poorest speed control?
a) Differentially compounded motor
b) Cumulatively compounded motor
c) Shunt motor
d) Series motor
In variable speed motor ____________
a) Stronger commutating field is needed at low speed than at high speed
b) Weaker commutating field is needed at low speed than at high speed
c) Same commutating field is needed at low speed and at high speed
d) Cannot be determined
The speed of a motor falls fromrpm at no-load torpm at rated load. The speed regulation of the motor is ____________
Which of the following is not the method of speed control in DC series motor?
b) Tapped-field control
c) Variable resistance in series with armature
d) Series- parallel control
For speed reversal, field control method is suitable.
For large motors what is the ratio of compensating winding is required for increasing the speed of the motor?
In diverter resistor field control method of DC series motor, variable resistor is added ________
a) In parallel with field
b) In series with field
c) In parallel with armature
d) In parallel with load
Why it is advisable to use inductively wound diverter resistor?
a) To make speed control on more range
b) For long-life of machine
c) Cost efficient
d) To avoid oscillations in speed
For higher diverter resistance, speed-torque characteristic will lie ____________
a) Above speed-torque characteristic of lower resistance
b) Below speed-torque characteristic of lower resistance
c) On the speed-torque characteristic of lower resistance
d) Cannot say
In tapped field control method ____________
a) A variable resistor is connected in parallel
b) A variable resistor is connected in series
c) Field winding is made with more out pins
d) Another field winding is added with the previous one
Which of the following method will not give many speed values for a DC series motor?
c) Field tapped
d) All field control methods will give many speed values
In series-parallel speed control method ______________
a) Speed given by parallel connection is more
b) Speed given by series connection is more
c) Both speeds can be equal
d) Will depend on other parameters
Where diverters are used?
a) In shunt motors
b) In series motors
c) In both motors
d) All other motors except shunt and series motors
What will happen to the speed of a series motor if the temperature of armature resistance is increased?
a) Not change
d) Cannot be determined
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