Q7 Answer - 2024 Jun Plant Exam

7.1 Identifying DC Motor Types and Descriptions

Each circuit represents a different type of DC motor configuration:

(a) Separately Excited DC Motor

• The field winding is separately excited from an independent voltage source.

• Provides precise control over the field current and, hence, motor performance.

(b) Shunt Wound DC Motor

• The field winding is connected in parallel (shunt) with the armature winding.

• Offers nearly constant speed under varying load conditions.

(c) Series Wound DC Motor

• The field winding is connected in series with the armature winding.

• Provides high starting torque but has poor speed regulation.

(d) Compound Wound DC Motor

• Has both series and shunt field windings.

• Combines the high starting torque of series motors with the good speed regulation of shunt motors.

7.2 Methods of Speed Control in a DC Motor

• Armature Voltage Control:

  • Varying the supply voltage to the armature to control speed.

  • Used in applications requiring fine speed control, such as traction systems.

• Field Flux Control:

  • Adjusting the current in the field winding to change the magnetic flux and alter speed.

  • Common in applications where a wide speed range is needed.

7.3 Advantages of Induction Motors

• Simple and Rugged Construction:

  • Induction motors have fewer moving parts, making them highly durable and reliable.

• Low Maintenance and Cost-Effective:

  • No need for commutators or brushes, reducing maintenance costs.