Effect of Armature Reaction on DC Generator

by Starlight Generator dieselgeneratortech

The effect of armature reaction on DC generator

Armature reaction has a great influence on the operation of DC generator, which makes the magnetic field of half pole strengthen. When the magnetic field on the other half weakens, will cause the larger the load and the stronger the magnetic field distortion caused by armature reaction. The result will destroy the normal commutation of armature winding elements, easily cause sparks and worsen the working conditions of the generator. At the same time, the armature reaction will make the flux density at the pole shoe tip, cause the maximum voltage between the commutators to be too high, and also easily cause sparks or even generator ring fire.

Add additional poles to compensate for the distorted flux. For large generator, adding compensation winding on the top of the main pole can make the flux distribution abnormal and correct.

The effect of armature reaction on commutation of DC generator

The armature reaction will distort the air gap magnetic field, which will have an adverse effect on the commutation of the DC generator:

(1)Because the air gap magnetic density at the geometric neutral is no longer zero, therefore, the induced electromotive force will inevitably be generated in the reversing element (the brush is in contact with the reversing piece connected to the element at the geometric neutral), which makes reversing difficult.

(2)The distortion of air gap magnetic field makes the voltage on commutator uneven, especially when the load of generator changes suddenly, it forms strong armature reaction and air gap magnetic field is serious distortion. It is possible to make the potential difference between two adjacent commutators exceed a certain limit, resulting in potential difference spark. And ring fire may occur as the arc lengthens. Commutation is a special problem of DC generator. If the commutation is not good, sparks will be generated between the commutator and the brush. If the spark exceeds a certain degree, the brush and commutator will be burnt out, which will seriously affect the operation of the generator. In addition, sparks will produce electromagnetic waves, which will interfere with wireless communication.

There are many reasons for sparking. In addition to electromagnetic reasons, there are also mechanical reasons. In the reversing process, there are also factors such as electrochemistry and electrothermal. They are intertwined with each other and the process is quite complex.