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.
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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 as armature reaction. There is an axis or, you may say, a plane along which armature conductors move parallel to the flux lines and, hence, they do not cut the flux lines while on that plane. MNA Magnetic Neutral Axis may be defined as the axis along which no emf is generated in the armature conductors as they move parallel to the flux lines.
Brushes are always placed along the MNA because reversal of current in the armature conductors takes place along this axis. GNA Geometrical Neutral Axis may be defined as the axis which is perpendicular to the stator field axis. Armature reaction The effect of armature reaction is well illustrated in the figure below. Consider, no current is flowing in the armature conductors and only the field winding is energized as shown in the first figure of the above image.
In this case, magnetic flux lines of the field poles are uniform and symmetrical to the polar axis. The 'Magnetic Neutral Axis' M. The second figure in the above image shows armature flux lines due to the armature current.
Field poles are de-energised. Now, when a DC machine is running, both the fluxes flux due to the armature conductors and flux due to the field winding will be present at a time. The armature flux superimposes with the main field flux and, hence, disturbs the main field flux as shown in third figure the of above image.
This effect is called as armature reaction in DC machines. The adverse effects of armature reaction: Armature reaction weakens the main flux. In case of a dc generator , weakening of the main flux reduces the generated voltage.
Armature reaction distorts the main flux, hence the position of M. Brushes should be placed on the M. So, due to armature reaction, it is hard to determine the exact position of the MNA For a loaded dc generator, MNA will be shifted in the direction of the rotation.
On the other hand, for a loaded dc motor , MNA will be shifted in the direction opposite to that of the rotation.
How to reduce armature reaction? Usually, no special efforts are taken for small machines up to few kilowatts to reduce the armature reaction. But for large DC machines, compensating winding and interpoles are used to get rid of the ill effects of armature reaction.
Compensating winding: Now we know that the armature reaction is due to the presence of armature flux. Armature flux is produced due to the current flowing in armature conductors. Now, if we place another winding in close proximity of the armature winding and if it carries the same current but in the opposite direction as that of the armature current, then this will nullify the armature field. Such an additional winding is called as compensating winding and it is placed on the pole faces.
Compensating winding is connected in series with the armature winding in such a way that it carries the current in opposite direction. Interpoles: Interpoles are the small auxiliary poles placed between the main field poles.
Winding on the interpoles is connected in series with the armature. Each interpole is wound in such a way that its magnetic polarity is same as that of the main pole ahead of it. Interpoles nullify the quadrature axis armature flux. Coronavirus safety tips - Wash your hands regularly for 20 seconds, with soap and water or alcohol-based hand rub. Cover your nose and mouth with a disposable tissue or flexed elbow when you cough or sneeze.
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Armature Reaction in a DC Generator
There are two kinds of magnetic fluxes acting in DC Generator; the first one is because of the stator poles called main flux, while the second one is because of the current flowing in the armature called armature flux. This armature flux weakens and distort the main flux, thus the overall effective flux in DC Generator decrease. This mutual action of armature flux on the main field flux is known as armature reaction. The following figure shows: i Main flux ii flux due to armature current iii overall effective distorted flux. Overall flux is less than the field flux because saturation occur at the pole tip B of the field pole due to higher field flux, thus increase in the flux at pole tip B is less than the decrease in the flux at pole tip A.
Armature reaction in DC Generator
Definition: The armature reaction simply shows the effect of armature field on the main field. In other words, the armature reaction represents the impact of the armature flux on the main field flux. The armature field is produced by the armature conductors when current flows through them. And the main field is produced by the magnetic poles. Consider the figure below shows the two poles dc generator.
An Overview of Armature Reaction
You may know that Google is tracking you, but most people don't realize the extent of it. Luckily, there are simple steps you can take to dramatically reduce Google's tracking. Armature reaction is effect of armature flux on main field flux. Basically there are two windings in a dc motor - Armature winding on rotor and field winding on stator. When we excite the field winding, it produces a flux which links with the armature. This causes an emf and hence a current in the armature. This current in armature produces another flux which lags the main flux.