Effects of Armature Reaction
- The influence of the magneto motive force (mmf) created by the armature winding or current on the main field flux generated by the field or stator winding is termed armature reaction. This effect has two unfavorable outcomes first is it distorts the primary field and diminishes its overall flux. When distortion occurs there is a cross magnetizing effect while reduced flux results in demagnetization. In essence armature reaction alters the distribution of the main field around the air gap periphery and induces demagnetization within the machine. The demagnetizing impact of armature emf typically reduces total pole flux by around 1 to 5% from no load to full load.
- Iron losses in the pole shoes and teeth depend on the highest flux density they handle. When the main field flux distorts the maximum density under load surpasses that at no load. Consequently the iron losses become more noticeable during operation compared to when the machine is idle.
- Armature reaction leads to a rise in the peak gap flux density causing an increase in the maximum voltage across neighboring commutator segments during operation. If this voltage surpasses 30 V sparking might occur between these adjacent commutator segments.
- Armature reaction moves the brush axis away from GNA, causing a non-zero flux density along the interpolar axis. Consequently, coils undergoing commutation experience induced e.m.f. aiming to sustain the original current direction. This challenge makes commutation harder and results in delayed commutation.
Armature Reaction In DC Machines
In DC machines the term armature reaction describes the distortion of the magnetic field brought on by the current flowing through the armature winding. The machine’s overall magnetic field is affected by the magnetic field produced by the armature as it carries electricity. The machine’s performance especially in terms of voltage regulation & commutation may be impacted by this interaction which may result in changes to the neutral plane. For DC machines to operate steadily and effectively the armature reaction needs to be taken into account and compensated for by engineers.
In a DC machine, there are two types of magnetic forces present one is the armature flux & the main field flux. When the armature flux affects the main field flux it is called an armature reaction.
Table of Content
- MNA And GNA
- Cases Armature reaction
- How to reduce Armature Reaction
- Effects of Armature Reaction
- Applications of Armature Reaction