Armature reaction in a DC machine:
Armature reaction refers to the magnetic field produced by the armature current in a DC machine. It affects the main field flux distribution and can have both desirable and undesirable effects on the machine's performance. The armature reaction is mainly caused by the load current in the armature.

Explanation:
When a current flows through the armature winding of a DC machine, it produces its own magnetic field. This magnetic field interacts with the main magnetic field produced by the field winding, resulting in a shift in the flux distribution within the machine. This phenomenon is known as armature reaction.

Effect of armature reaction:
The armature reaction has several effects on the DC machine, including:
1. Magnetic field distortion: The armature reaction distorts the main magnetic field, causing a non-uniform distribution of flux density across the air gap. This can lead to uneven torque production and increased losses in the machine.
2. Cross-magnetizing effect: The armature reaction can cause a component of the magnetic field to be perpendicular to the main field, resulting in a cross-magnetizing effect. This causes a reduction in the effective field flux, leading to a decrease in the machine's performance.
3. Demagnetizing effect: In certain operating conditions, the armature reaction can demagnetize the field poles, reducing the magnetic field strength and causing a decrease in the machine's performance.
4. Commutation issues: Armature reaction can also affect the commutation process in a DC machine. It can lead to sparking at the brushes and result in poor commutation, leading to increased electrical losses and reduced machine efficiency.

Source of armature reaction:
The armature reaction is mainly produced by the load current in the armature. As the load current flows through the armature winding, it generates a magnetic field that interacts with the main field produced by the field winding. The strength and direction of the armature current determine the extent and nature of the armature reaction.

Conclusion:
In conclusion, the armature reaction in a DC machine is mainly produced by the load current in the armature. It creates a magnetic field that interacts with the main field, causing various effects on the machine's performance. Understanding and managing the armature reaction is important for optimizing the operation of DC machines.

As we know that armature reaction is produce due to the armature flux. and armature flux produce due to the current flowing in the in armature conductors.