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How do interpoles reduce armature reaction in dc machine? What is exactly the cross magnetizing effect ??
Armature reaction refers to the effect of the armature current on the magnetic field produced by the field coils in a DC motor. When the armature current flows through the armature windings, it creates its own magnetic field that interacts with the field produced by the field coils, causing a distortion in the overall magnetic field.
Interpoles, also known as commutating poles, are small auxiliary poles added to the main poles in a DC motor. The purpose of interpoles is to counteract the effects of armature reaction by producing a magnetic field that is opposite in direction to the armature reaction, thus reducing the distortion in the main magnetic field.
Cross magnetizing effect occurs when the magnetic field produced by the armature current is not perpendicular to the magnetic field produced by the field coils, resulting in a torque that is not in the desired direction. This can lead to a decrease in the motor's efficiency and can also cause mechanical stress on the motor's components.
No, armature reaction cannot be eliminated completely. However, it can be minimized by using interpoles and properly designing the motor's geometry and magnetic circuit. The amount of armature reaction depends on factors such as the motor's design, load, and speed.
Apart from using interpoles, the effects of armature reaction can also be compensated for by adjusting the field current or by using compensating windings that produce a magnetic field that is in the opposite direction to the armature reaction. Another method is to use a commutating winding that helps to shift the brushes to a position where they are aligned with the neutral axis of the armature, reducing the effects of armature reaction.