What Is DC Generator Armature Reaction

by Starlight Generator dieselgeneratortech

What is armature reaction?

In a DC generator, armature reaction means the effect of armature magnetomotive force on the fundamental wave of the main pole magnetic field under symmetrical load.

It is assumed that the only magnetomotive force acting on the DC generator is generated by the stator magnetic field. However, the magnetic field generated by the current in the armature winding is called the armature magnetic field, and the axis of the armature magnetic field intersects the axis of the main magnetic field vertically. No matter in the motor or generator, the distortion and weakening of the magnetic field occur. The reaction caused by armature magnetomotive force is usually called armature reaction.

The effect of armature magnetic field on the main magnetic field will distort the main magnetic field and produce armature reaction:

a.Armature reaction under pure resistive load.

The electromotive force of the armature magnetic field is the same as the phase of the current. The armature magnetic field distorts the main magnetic field, half strengthens and half weakens.

b.Armature reaction under pure inductive load.

The current of armature magnetic field lags 90 degrees behind electromotive force, the electromotive force generated by armature magnetic field is opposite to that generated by main magnetic field. Therefore, the EMF of the main magnetic field is weakened, this is why the voltage drops when there are inductive elements in the three-phase circuit. This is called longitudinal axis demagnetization armature reaction.

c.Armature reaction under pure capacitive load.

The current of armature magnetic field is 90 degrees ahead of electromotive force, because the armature magnetic field is 90 degrees to the main magnetic field, The electromotive force generated by the armature magnetic field is in the same direction as that generated by the main magnetic field. Therefore, enhanced EMF of main magnetic field. This is why the terminal voltage rises when there are capacitive elements in the three-phase circuit. This is called longitudinal axis auxiliary magnetoarmature reaction.

Armature reaction classification

a.Quadrature armature reaction.

The quadrature axis armature reaction is the influence of the quadrature axis armature magnetomotive force on the main pole magnetic field. Here, in order to analyze the problem simply, we assume that ① the magnetic field is unsaturated, ② the armature steering of the generator is counter clockwise, and the motor is clockwise. It can be seen that:

(1)the cross axis armature magnetic field can demagnetize the main pole magnetic field in half pole, increase magnetic action in the other half of the pole, which causes air gap magnetic field distortion, offset the geometric neutral at a position where the flux density on the armature surface is equal to zero.

(2) when saturation is not considered, there is neither demagnetization nor demagnetization in the cross axis armature reaction. When saturation is considered, it plays a role of demagnetization.

b. Direct axis armature reaction.

When the brush is not on the geometric neutral line, the direct axis armature reaction occurs.

(1)In case of generator, the brush moves an included angle in the direction of rotation, for the magnetic field of the main pole, the direct axis reacts to demagnetize. If the brush moves an included angle against the rotation direction, the direct axis armature reaction will be magnetized.

(2)In the case of motors, the opposite is true.