Are you curious to know what is armature reaction? You have come to the right place as I am going to tell you everything about armature reaction in a very simple explanation. Without further discussion let’s begin to know what is armature reaction?
Armature reaction is a phenomenon that occurs in DC motors when the current flowing through the armature windings interacts with the magnetic field produced by the field windings. This interaction leads to changes in the magnetic field distribution within the motor, affecting its performance. In this blog, we will explore the concept of armature reaction, its causes, effects, and its significance in the operation of DC motors.
What Is Armature Reaction?
In a DC motor, the armature winding is the winding where the current flows to produce the rotational motion. The field windings, on the other hand, generate the magnetic field within the motor. When current flows through the armature winding, it creates its own magnetic field, which interacts with the magnetic field produced by the field windings.
Causes And Effects Of Armature Reaction:
- Magnetic Field Distortion: The magnetic field produced by the armature winding interacts with the field winding’s magnetic field. This interaction causes a distortion in the overall magnetic field distribution within the motor. The armature field opposes or weakens the main field, resulting in a deviation from the ideal uniform magnetic field.
- Brush Shift: Armature reaction can cause a shift in the position where the brushes make contact with the commutator. This shift occurs due to the changes in the magnetic field distribution caused by the armature reaction. Brush shift can lead to uneven commutation, increased sparking, and additional electrical losses.
- Back EMF Variations: Armature reaction affects the back electromotive force (EMF) generated in the motor. The back EMF opposes the supply voltage and determines the speed of the motor. The distortion in the magnetic field due to armature reaction alters the back EMF, leading to variations in the motor’s speed and performance.
- Torque Ripple: Armature reaction can introduce torque ripple, which refers to fluctuations in the motor’s output torque. The non-uniform magnetic field distribution caused by armature reaction results in uneven forces acting on the armature conductors, leading to torque variations.
Compensating For Armature Reaction:
To minimize the adverse effects of armature reaction, various techniques are employed in DC motor design and operation:
- Use of Interpoles: Interpoles, also known as commutating poles, are additional small poles placed between the main field poles. These interpoles generate a field that counteracts the armature reaction, reducing the distortion in the magnetic field and improving commutation.
- Brush Shifting: In some cases, the position of the brushes can be adjusted to compensate for the brush shift caused by armature reaction. By shifting the brushes in the opposite direction to the actual brush shift, the commutation process can be improved.
- Field Weakening: Field weakening involves reducing the field current in the field windings, thereby decreasing the strength of the main magnetic field. This approach reduces the impact of armature reaction on the motor’s performance.
Conclusion:
Armature reaction is an important phenomenon that affects the operation of DC motors. Understanding its causes, effects, and methods of compensation is crucial for engineers and technicians working with DC motor systems. By mitigating the adverse effects of armature reaction through the use of techniques such as interpoles, brush shifting, and field weakening, the performance, efficiency, and reliability of DC motors can be optimized. Armature reaction serves as a key consideration in motor design and operation, enabling engineers to harness the full potential of DC motor technology.
FAQ
What Is The Armature Reaction In A Dc Machine?
The current flowing through the armature conductors creates a magnetic field, which is called as armature flux. This armature flux distorts and weakens the magnetic flux produced by the main poles. This effect of armature flux on the main flux is known as armature reaction.
What Is The Armature Reaction Formula?
Armature resistance drop: As the load current increases, more and more voltage is consumed in the ohmic resistance of the armature circuit. Hence, the terminal voltage V=E−IaRa is decreased where E is the induced mmf in the armature under load condition.
What Is The Main Effect Of Armature Reaction?
Armature reaction has two undesirable effects: First, it distorts the main field. Secondly, it reduces the main field flux or both. When the main field is distorted, then there will be a cross magnetizing effect.
What Are The Types Of Armature Reaction?
Types of Armature-Reaction
- Demagnetization of the stator field.
- The cross magnetization of the stator field.
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