An Overview of Armature Reaction

The DC generator, there are two windings namely field winding and armature winding. The field winding can be used for generating main flux which is known as the magnetic field. The armature winding can be used for generating armature current. This winding can also generate magnetic flux which is known as armature flux. This armature flux twists and declaims the major flux posing troubles for the good DC generator operation. The act of armature flux over the major flux is known as armature reaction. This article discusses an overview of armature-reaction in dc generator, alternator and dc machine.

What is Armature Reaction?

In a DC machine, two kinds of magnetic fluxes are present; ‘armature flux’ and ‘main field flux’. The effect of armature flux on the main field flux is called an armature-reaction

The EMF can be induced within the armature conductors whenever they slash the lines of the magnetic field. There is a plane or an axis with armature conductors which can be moved parallel toward the lines of flux & therefore, they do not slash the lines of flux through the axis.


The Magnetic Neutral Axis (MNA) can be defined as the plane along which no EMF can be generated within the armature conductors because they flow parallel toward the lines of flux. Brushes are constantly arranged with MNA due to reverse of current within the armature conductor’s takes place along this plane. The Geometrical Neutral Axis (GNA) can be defined as the plane which is perpendicular toward the stator field plane.

Types of Armature-Reaction

The armature-reaction is one kind of magnetic field effect which is occurred by the flow of current throughout the armature conductors over the stator magnetic field. Generally, these are classified into two types which include the following.

  • Demagnetization of the stator field
  • The cross magnetization of the stator field

The Demagnetization reduces otherwise weakens the main flux, whereas the cross magnetization distorts the main flux.

Armature Reaction in DC Machines

Consider when there is no flow of current within the armature conductors & only the field winding is strengthened. So, the field pole’s magnetic flux lines are consistent as well as balanced to the polar plane. The MNA (Magnetic Neutral Axis) corresponds with the GNA (Geometric Neutral Axis).

In the armature flux lines, field poles are not strengthened because of the armature current. At present, as a DC machine is in operation; both the fluxes like flux can be occurred because of the armature conductors & flux can be occurred because of the field winding will be there at a time.

The armature flux overlay with the major field flux & therefore interrupts the major field flux, which is known as armature reaction in DC machines.

The armature-reactions can be reduced in DC machines like the following.

  • By offering inter poles among major poles otherwise reimbursing winding if necessary.
  • By decreasing the slice of the pole pieces then it becomes extremely saturated as well as provides huge reluctance toward the cross field.
  • By utilizing the equalizer ring to reduce the armature winding flux to reduce the armature-reaction

Armature Reaction in Alternator

The armature reaction in an alternator is, a 3-phase voltage can be induced by the stator winding, because of the revolving magnetic field from the rotor. Here the circuit of the stator is called an armature circuit.

When the stator doesn’t have any load across it, then the total voltage can be induced at the winding of the stator which comes out like the terminal voltage. But, when we fix a load across the stator, current flows across it, which produces its own flux known as stator flux.

The produced stator flux distorts the main flux as a result of which the terminal voltage across the machine is not equal to the voltage initially induced. This effect of the stator (armature) is known as armature-reaction.

The effect of the armature reaction on the terminal voltage of the alternator is not the same for all conditions.

Effect of Armature-Reaction

The armature-reaction effects due to the following reasons.

Because of the armature-reaction, the flux density of above one-half of the pole enhances as well as the remaining half will be decreases. The whole flux which can be generated by every pole is somewhat less because of reducing the terminal voltage of the magnitude. The effect because of the reduction in total flux by the armature-reaction is called as the demagnetizing effect.

The resulting flux can be distorted, and the magnetic neutral axis direction can be moved with the resultant flux direction in the generator, & it is reverse toward the resultant flux direction in the motor.

The armature-reaction provokes flux during the neutral region, & this flux produces the voltage that reasons for the commutation problem. The MNA plane is the axis where the induced EMF value becomes zero, & the GNA separates the armature core into two equivalent parts.

Armature Reaction in DC Generator

There are two types of magnetic fluxes working in DC generator like the main flux & armature flux. Here the primary flux will occur due to the stator poles whereas the second flux will occur due to the flow of current within the armature. Here the armature flux declines and changes the major flux, therefore the total effective flux within DC Generator will be reduced.

The armature flux’s mutual action over the major field is named as armature-reaction in DC generator.

Armature-Reaction Nature

The nature of the armature-reaction includes the following.

  • The flux of this can be stable within magnitude as well as it turns at synchronous speed.
  • It is cross magnetizing whenever the generator offers a load on power factor ‘1’.
  • Whenever the generator offers a load on leading power factor then the armature-reaction can be partially demagnetizing & cross-magnetizing.
  • Armature flux can be performed as separately of main field flux.

Thus, this is all about armature reaction. Generally, for small machines there is no particular effort is required to decrease the armature-reaction. However, for huge DC machines, inter poles as well as compensating winding are mandatory to reduce the effects of armature-reaction. Here is a question for you, what are leading pole tips in armature-reaction?