How Armature Reaction effects the DC Machine Explained


In this article, we are going to discuss what is Armature Reaction in DC Generator and what are the actual effects of armature reaction. Armature reaction generally happens in DC Generators but it can be seen in AC Generator also. To better understand we will discuss about the DC generator only but remember that the concept for both DC and AC generators is almost the same.


Armature reaction dc machine



What is Armature Reaction?


The reaction between flux produced by the armature coil and flux produced by the main field coil is called Armature Reaction. Or, in other words when the armature flux impacts the main field flux then it is called an Armature reaction. It will be heard better if we say armature reaction on the main field.


When and Why Armature Reaction Happens?


You can understand the armature reaction better when you know the basic working principle of a DC generator. The working principle of the DC generator is very simple when the armature is rotated by a prime mover and the main field flux cut by the armature conductors and According to Faraday's Law, an EMF will induce in the armature coil. Thus a DC generator converts mechanical energy into electrical energy.

When the generator is running in no or the armature coil is open-circuited, no current will flow through the armature coil. When the generator is connected to a load, or its armature coil closed circuited, an electric current(equal to load current) will flow through the armature coil. This flow of current will causes the production of magnetic flux by the armature coil. And this magnetic flux produced by the armature coil will affect the main field flux which known as Armature Reaction.

So, Armature Reaction happens in a DC generator when it is connected with a load. The cause of armature reaction is the flow of electric current through the armature coil when it is loaded.



Effects of Armature Reaction in DC Generator


There are mainly two major effects of armature reaction towards the main field flux-

1. Cross Magnetizing Effect
2. De Magnetizing Effect


Cross Magnetizing Effect in DC Machine


In simple words, when the armature flux force to distorted the main field flux then it is called Cross Magnetizing Effect.
In the cross magnetizing effect, armature flux force to shift the position of MNA(Magnetic Neutral Axis) which further effect to the smooth running of the generator and may causes the sparking on brushes. In general, MNA is perpendicular to the flux lines of the main field flux. In a DC generator, the MNA generally shifted towards the direction of the rotation due to armature reaction.



Demagnetizing Effect in DC Machine


In simple words, when the armature flux weakens the main field flux then it is called Demagnetizing effect. Armature flux always opposite to the main field flux, the armature flux always tries to weaken or reduce the strength of the main field flux.

As the strength of the main field flux decrease, so it will affect the generated voltage or we can say armature reaction in a DC generator causes to reduce the generated voltage.



Methods to Reduce Armature Reaction


Generally, two methods are used to reduce armature reaction in DC machine - 

1. Compensating Winding
2. Interpole


Compensating Winding in DC Machine


Compensating Winding is placed in the pole face and it is connected with the armature coil in series but in opposite direction. So when the armature winding is closed circuited, current will flow through both armature coil and compensating winding. Compensating winding will produce flux in opposite direction to the armature flux, so the armature flux will be weaker and as a result the armature reaction also be reduced.



Interpole in DC Machine


Interpoles are the smaller size auxiliary poles placed between main poles. Interpole also connected in series with the armature coil in opposite direction. Interpole also does the same as the compensating winding to reduce the armature reaction.


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How Armature Reaction effects the DC Machine Explained How Armature Reaction effects the DC Machine Explained Reviewed by Author on 4/04/2021 Rating: 5
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