3.12 Cat B

What is the advantage of a series field motor?

• Its RPM is very stable, even with load changes.
• It has the highest starting torque of all electric motors.
• It doesn't need brushes and slip rings.
• It has the greatest Voltage drop over the field windings of all electric motors

What is the advantage of a shunt field motor?

• Its RPM is very stable, even with load changes.
• It has the highest starting moment of all electric motors.
• It doesn't need brushes and slip rings.
• It has the highest current draw through the field windings of all electric motors

Which type of motor is suitable for use as a starter?

• Series field motor
• Shunt field motor
• Asynchronous motor
• Parallel wound induction motor

What is the purpose of the excitation winding in a DC machine?

• To generate a static magnetic field in the stator.
• To generate a static magnetic field in the rotor.
• To increase the output power.
• To generate a Rotating Magnetic Field (RMF) in the stator

How is the rotation direction of a DC machine changed?

• By interchanging the supply leads.
• By reversing the current direction in the armature winding or the excitation winding.
• By reversing the current direction in the stator winding.
• By increasing the frequency of the supply voltage

Why are interpoles fitted to the main poles of DC machines?

• To increase the flux density of the field.
• To boost the field strength.
• To counter the effects of armature reaction on the main field.
• To create a rotating magnetic field in the stator

Which part provides the power supply for the armature in a DC machine?

• Excitation winding
• Pole shoe
• Commutator
• The rotating rectifying diode pack.

What is the purpose of the commutator in a DC motor?

• To generate a stationary magnetic field into the motor.
• To energise the coil at the appropriate time in the revolution of the motor.
• To generate a rotating magnetic field into the motor.
• To reduce the resistance in the armature windings

How is the excitation winding and the armature winding connected in a Shunt Wound DC Motor?

• Series
• Crossed
• Intermittent
• Parallel
• Series-parallel

What is the effect on the armature cross-field with an increase in armature current in a DC motor?

• The cross-field is weakened.
• The cross-field is strengthened.
• The cross-field is not influenced.
• The cross-field reverses.