PHYSICS: D.C. MACHINE 02/08 Online Test

Parallel operation of two or more D.C. compound generators, is possible provided
Polarity of incoming generator is same as that of bus bar
All the series fields run in parallel by means of equalizer connection
Series fields of all generators are either on positive side or negative side of the armature
Voltage of the incoming generator is same as that of bus bar
The speed of a D.C motor may be varied by varying
Applied voltage
Field current
Resistance is series with armature
Any of the above
Which of the following speed control methods of D.C motor require auxiliary motor?
Flux control
Armature control
Voltage control
Ward-Leonard control
The efficiency of a D.C machine is maximum when
Variable losses are equal to constant losses
Stray losses are equal to copper losses
Field copper losses are equal to armature copper losses
Magnetic losses are equal to wind age loss
Compensating winding in a D.C machine is connected
In series of inter pole winding.
In series of field winding
In series of armature winding
Directly across the supply
Mark the correct statement below in respect of armature control of a D.C Shunt motor
Increase in armature voltage increases motor speed and also the full-load torque capability of the motor
Increase in armature voltage decreases motor speed while the full-load torque capability is unaffected
Increase in armature voltage (with fixed current) increases motor speed while the full-load to capability of the motor remains unaffected
Increase in armature voltage decreases motor speed and also the full-load torque capability of the motor
In a D.C. generator probable cause of failure to build up voltage is
Imperfect brush contact
No residual magnetism in the generator due to faulty shunt connections
Field resistance higher than the critical resistance
All of the above
The critical resistance of a D.C generator refers to the resistance of
Load
Brushes
Field
Armature
The efficiency of a D.C shunt generator becomes maximum when the
Stray losses are equal to constant losses
Armature copper losses are equal to constant losses
Magnetic losses are equal to mechanical losses
Field copper losses are equal to constant losses
Which of the following D.C motor has approximately constant speed? .
Shunt motor
Series motor
Cumulatively compound motor
All of the above
f the supply voltage in a shunt motor is increased, which of the following will decrease?
Full load current
Full load speed
Starting torque
None of the above
Why the armature winding coils of a D.C machine are placed in number of slots around the periphery, instead of placing them in only two slots?
To make the armature balanced
To have minimum heat dissipation from the armature
To get sinusoidal e.m.f. At the output terminals of the machine
To get maximum generated e.m.f. In the armature.
Which device changes the alternating e.m.f generated by the D.C generator, in its armature coil, to D.C?
Slip ring.
Rectifier
Rotary converter
Commutator
If the D.C series motor is started at no load, it will
Run at very high r.p.m.
Run with excessive noise
Burn out
Not start
Two series motors are mechanically coupled. One machine is run as motor and the other as generator. The iron and friction losses of the machines will be identical when
Their speeds and excitations are identical
Their speeds are equal and back emf are half the supply voltage
Their ratings and armature sizes are identical
Their speeds are identical
In the block diagram of a separately excited D.C motor, the armature induced e.m.f appears as
Disturbance input
Positive feedback
Negative feedback
Output
The most economic method of electrical braking is
Plugging
Dynamic braking with self excitation
Regenerative braking
Dynamic braking with separate excitation
Stray losses in D.C machine are
Wind age loss
Magnetic losses
Mechanical losses
All of the above
Which of the following statement is true while starting a D.C shunt motor
Reduced armature voltage but full field voltage should be applied and. all regulator resistance should be cut out in the field circuit
Rated armature and rated field voltage should be applied and full regulator resistance should be included in the field circuit
Reduced armature voltage and reduced field voltage should be applied and full regulator resistance should be included in the field circuit
Rated armature and rated filed voltage should be applied and full regulator resistance should be cut out on the field circuit.
Which of the following type of D.C motor is least used?
Series motor
Differentially compound motor
Permanent magnet motor
Cumulative compound motor
Which of the following parts of a D.C motor can sustain the maximum temperature rise?
Slip rings
Commutator
Field windings
Armature windings
Description:

This is test is a part of a series of eight test which helps students to check the level of knowledge in Electricity, specifically in the DC Machine in Physics.

Discussion

k.rama krishna

in que 2...speed vary with changing vol,Ra,If... nt only If

3349 days ago

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