1 Briefly describe the main difference between a generator and a motor when energy transfer is taken into account.

Here are the answers to the questions:

4.1 Briefly describe the main difference between a generator and a motor when energy transfer is taken into account.
A generator converts mechanical energy into electrical energy. A motor converts electrical energy into mechanical energy.

4.2 List the two main parts of a DC machine and explain each briefly.

• Stator: This is the stationary part of the DC machine. It houses the field windings, which create the stationary magnetic field necessary for operation.
• Rotor (Armature): This is the rotating part of the DC machine. It contains the armature windings where the main energy conversion (mechanical to electrical in a generator, electrical to mechanical in a motor) takes place.

4.3 Name TWO types of DC motors other than compound wound motor and give an application for each.

• Series Wound Motor: This motor delivers high starting torque and its speed varies significantly with the load.
  • Application: Used in applications requiring high starting torque, such as electric trains or cranes.
• Shunt Wound Motor: This motor offers a relatively constant speed under varying load conditions.
  • Application: Suitable for applications requiring constant speed, like lathes or pumps.

4.4 Explain the difficulties of commutation in a DC machine.
The main difficulty in commutation is the reversal of current in the armature coils as they pass under the brushes. This process involves a brief short-circuit of the coil by the brush, which can lead to sparking at the brushes due to the inductance of the coil resisting the current change. This sparking causes wear on the brushes and commutator segments.