In a DC machine, the angle between the stator and rotor fields is

Electrical Engineering XYZ MCQs

In a DC machine, the angle between the stator and rotor fields is:

1. Dependent upon the load
2. 90^o
3. 0^o
4. 180^o

Correct answer: 2. 90^o

Explanation: In a DC machine, the stator field is typically generated by the field winding, and the rotor field is produced by the armature winding when current flows through it. The angle between these two fields is known as the electrical angle.

In an ideal situation, when the machine is not loaded and there is no armature reaction, the stator field and the rotor field would be perfectly aligned with each other, resulting in an electrical angle of 0°. However, in practical situations, due to armature reaction and other factors like load and magnetic saturation, the alignment is not perfect.

At no load, the electrical angle might be very close to 0°, but as the load increases, the armature reaction causes the rotor field to lag behind the stator field. The maximum angle between them occurs at full load and is typically around 90°. This 90° lag is important for the generation of torque in DC machines.

Therefore, the correct answer is 90°, as it represents the typical angle between the stator and rotor fields in a loaded DC machine.