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.
What is Armature Reaction?
The reaction between the flux produced by the armature coil and the 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. The opposition to the field flux by armature flux. Armature generally occurs in a direct current (DC) electric machine, such as a DC generator or a DC motor.
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 is 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 cause 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 is known as Armature Reaction.
So, Armature Reaction happens in a DC generator when it is connected to a load. The cause of the 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 cause 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 the 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 is 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 the 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 the armature coil and compensating winding. Compensating winding will produce flux in the opposite direction to the armature flux, so the armature flux will be weaker and as a result the armature reaction also be reduced. Sometimes it increases the overall resistance of the armature winding.
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 the opposite direction. Interpole also does the same as the compensating winding to reduce the armature reaction. Interpoles are used in a few machines because it increases the overall weight of the machine.
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How Armature Reaction effects the DC Machine Explained
Reviewed by Author
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April 04, 2021
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Reviewed by Author
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April 04, 2021
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