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Armature Reaction is the effect of magnetic flux set up by armature current The brushes of the DC machines are always placed in this axis, and hence this axis. armature reaction mmf gets added at this tip leading to considerable amount In some small d.c. machines the brushes are shifted from the position of the mag-. Commutation problem is not the only problem in DC machines. At heavy loads, the cross magnetizing armature reaction may cause very high.

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Armature Reaction in DC Machine

The MMF flux is uniformly distributed along admature magnetic axis. These are two principal methods by which the effect of armature reaction is overcome.

Help Center Find new research papers in: Due to this armature current will short circuit the coil and produce huge Fig 10 Armature Reaction short circuit circulating current and therefore I2R losses produced in armature winding and also results in sparking.

This phenomenon is thus known as the demagnetizing effect of cross magnetizing armature reaction, which is further compensated by the use of compensating windings. So neutral zone has shifted in the direction of rotation therefore brushes has been place in armatue new neutral zone.

So this amplitude keeps varying then the resultant could be in any direction depending upon the amount of load current as shown in Fig. Now, there is a current in the previous loading direction because all this add up inside the core this produce effect diagram as shown in Fig. The above problems are d.c.,achines by use of compensating winding. With complete compensation the main field is restored.

Armature reaction in DC Generator

They have the polarity of succeeding pole coming next in sequence of rotation in generator action and proceeding x.c.machines has passed behind in rotation sequence pole in motor action. And the GNA divides the armature core into two equal parts. In the d.c.machihes, an electromotive reqction is created by the relative motion of the armature and the field. Armature reaction is essential in amplidyne rotating amplifiers. Alternator Electric generator Inchworm motor. Now let us look at the effect of this armature reaction.


Mail will not be published required. Arkature reaction also comes in the way of good commutation. Fig 11 Commutating poles to reduced armature reaction Let the commutator which is placed and also have the brushes in the neutral zone.

Although distinctly separate these two sets of terminology are frequently used interchangeably or in combinations that include one mechanical term and one electrical term. Now, when the machine is loaded, the armature flux is directed along the inter polar axis the axis in between the magnetic poles and is triangular in wave shape.

The brush-setting method is satisfactory in installations in which the generator operates under a fairly constant load. Besides this the distortion of main field can be prevented by cancelling the effects of the flux produced by the armature current.

D.c.maxhines reaction is one of the reasons that causes generated emf in DC Generator to decrease. Now a resultant flux is known and therefore orthogonal to the plane is this and these would be neutral zone which is shown in Fig. The brush-setting method is the most common means of correcting for armature reaction in small generators d.c.machines producing approximately W or less. Inter polar windings are always kept in series with armature, so inter polar winding carries the armature current; therefore works satisfactorily irrespective of load, the direction of rotation or the mode of operation.


The inter pole is designed to neutralize the d.cmachines reaction mmf in the inter polar axis. The effect of the armature field is to distort the generator field and shift the neutral plane.

And the negative terminal brush is connected to winding which d.x.machines wound over There are many problems like high circulating current, poor this small pole and it is connected to negative terminal. Windings are held in slots in the rotor or armature covered by stator magnets.

Thus the compensating winding produces flux, which is completely opposite and equal in magnitude to the armature flux, hence both cancel the effect of each other and thus armature reaction is completely neutralized. MNA Magnetic Neutral Axis may be defined as the axis along which no reaxtion is generated in the armature conductors as they move parallel to the flux lines.

So in flows from this commutated pole windings. This is because commutation occurs rwaction the coils located on the brushes only, and the coil undergoing commutation comes under the influence of the alternate pole changes its location from north to south pole or vice rezction. The direction of current induces in the conductor is given by the Fleming right-hand rule. Click here to sign up. The variation of neutral zone position due to armature reaction is shown in the following figure.

AC asynchronous induction IM. This flash over may spread to the neighboring commutator segments, leading ultimately to a complete fire over the commutator surface from brush to brush. Home Electrical machines Power system Contact electricaleasy.