DC MOTORS

The rotating part of a DC Motor is known as __________.

• Pole

• Stator

• Armature

• Carbon brush

Carbon brushes are used on DC Motors to __________.

• Brush off carbon deposits

• Provide a path for flow of current

• Prevent sparking during commutation

• Prevent overheating of armature winding

Voltage equation for DC Motor is __________.

• V = E_b + I_aR_a

• V = E_b – I_aR_a

• E_b = V – I_fR_f

• E_b = V + I_aR_a

Condition for maximum power output for DC Motor is __________.

• E_t = V

• E_b = V/2

• E_b = I_aR_a/2

• E_b = I_aR_a + I_fR_f

The speed of a DC Motor is __________.

• Directly proportional to EMF as well as flux

• Inversely proportional to EMF as well as flux

• Directly proportional to back EMF and inversely proportional to flux

• Inversely proportional to back EMF and directly proportional to flux

The highest speed attained by DC shunt motor is __________.

• Higher than no-load speed at rated flux

• Lower than no-load speed at rated flux

• Equal to no-load speed at rated flux

• Equal to infinity at rated flux

In a DC Motor iron losses occurs in the __________.

• Yoke

• Field

• Armature

• None of these

The dummy coil in the DC machines is used to __________.

• Eliminate reactance voltage

• Eliminate armature reaction

• Eliminate harmonics developed in the machine

• Bring about mechanical balance of armature

And external resistance is added in series with the field of a DC shunt motor. When the motor runs, the effect of resistance is __________.

• To increase the speed of the motor

• To reduce the losses

• To reduce the speed of the motor

• To reduce the armature current of the motor

The speed of a dc shunt motor is required to be more than full load speed. This is possible by __________.

• Increasing the excitation current

• Increasing the armature current

• Decreasing to armature current

• Reducing the field current