Armature reaction in a DC machine
A. is in direct opposition to the main poles.
B. is in the same direction as the main poles.
C. makes an angle of 90° with the main pole axis.
D. makes an angle with the main pole axis which is load dependent.
Answer: C
Share your understanding of this question with the correct explanation.
The answer is C. makes an angle of 90° with the main pole axis.
Armature reaction is the magnetic field produced by the current flowing in the armature winding of a DC machine. The armature reaction field is at right angles to the main field, and it tends to distort the main field. This distortion can cause problems such as decreased efficiency, increased noise, and sparking at the brushes.
The amount of armature reaction is proportional to the armature current. As the armature current increases, the armature reaction field also increases. This can cause the main field to be weakened, which can lead to decreased efficiency and increased noise. In severe cases, the armature reaction field can be so strong that it can cause the motor to run backwards.
There are a number of ways to reduce the effects of armature reaction. One way is to use a compensating winding. A compensating winding is a winding that is placed on the stator of a DC motor. The compensating winding is designed to create a magnetic field that opposes the armature reaction field. This helps to keep the main field strong and prevents the problems caused by armature reaction.
Another way to reduce the effects of armature reaction is to use a brush shift. A brush shift is a mechanical adjustment that moves the brushes away from the neutral axis. This reduces the amount of armature reaction field that is at right angles to the main field.
Armature reaction is a common problem in DC machines. However, it can be minimized by using a compensating winding or by brush shifting.