ARMATURE REACTION IN D.C.MACHINES PDF

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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For example, in the above figure if the motor rotates clockwise, then for North Pole, the lower tip is leading tip and for South Pole upper tip is leading tip.

So, due to these problems like circulating current which itself heat up the winding and the other one is 3. Timeline of the electric motor Ball bearing motor Barlow’s wheel Lynch motor Mendocino motor Mouse mill motor. The brushes of the DC machines are always placed in this axis, and hence this axis is called the axis of commutation. Why not share it? AC asynchronous induction IM.

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. But compensating winding and commutating poles appreciably decrease this effect and greater part of overall losses in DC Generator is compensated. The demagnetizing mmf magneto armaure force thus produced is given by: However for a constant load current, the rotation of brush hanger mechanism find the correct neutral zone position and then good commutation is possible to achieve.

This armature flux weakens and distort the main flux, thus the overall effective flux d.c.macbines DC Generator decrease. The armature reaction changes the distribution of the magnetic field, which affects the operation of the machine.

Would you like to know more about DC Generator? The commutating poles are connected in series with the armature winding, but in such a design that they cancel the effect of armature conductor flux and hence we have left only the main field flux.

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Now upper field is acting like a rubber band, so it is trying to push the conductor in downward direction as shown in Fig. Views Read Edit View history. Fig 8 Resultant flux due to interaction between two fluxes Now the flux created by armature current is in the upward direction and the direction of north-south pole flux is right angle to armatude flux.

Therefore the brushes cannot be dynamically positioned as the load current changes. When the field flux enters into the armature, they may get distorted. Larger generators require the use of interpoles.

Armature reaction in DC Generator

On the left hand side of neutral zone, the flux is creating rings around conductors because there is current flowing within this loops and the direction is in clockwise which is given by the right hand rule. So therefore this flux which is created due to the load Because when the brushes are passing over that coil there is current of armature current flowing in and going to cause a a current flowing through that and there is an inductive problem.

This topic is focused on one particular aspect of DC Generator. Armature reaction also comes in the way of good commutation. In large machines subject to heavy overloads or d.c.macjines In small motors subject to sudden reversal and high acceleration.

Armature (electrical)

In other words, the armature reaction represents the impact of the armature flux on the main field flux.

Now flux ib produced due to the armature current and this flux always going to in this direction whatever may the position be of will resultant voltage being induced in the coil.

A growler d.c.mwchines used to check teaction armature for shorts, opens and grounds. The tip of the pole from where the armature conductors come into influence is called leading tip and the other tip opposite in direction to it will be the trailing tip. Due to cross magnetization, the magnetic neutral axis on load, shifts along the armafure of rotation in DC generator and opposite to the direction of rotation in DC motor. The armature conductors combine their MMF for generating the fluxes through the armature in the downward direction.

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Because of this one major problem that the brushes which were supposed to be located at in the neutral zone because in neutral zone there is no voltage induced in the coil there is no brush short circuit at the point and there is no problem there is no huge circulating current. Coils of the winding are distributed over the entire surface of the air gap, which may be the rotor or the stator of the machine.

Armature Reaction in DC Machine

The magnetic neutral axis of poles is always d.c.machinew to the axis of the resultant flux. In flows through the conductor is shown in Fig.

Armature reaction is an undesirable effect that should be overcome in D.c.machimes machine. This can be achieved by installing commutating poles in between two consecutive main poles. So this amplitude keeps varying then the resultant could be in any direction depending upon the amount of load current as shown in Fig. At high loads, this effect of armature reaction may cause excessive flux density in the trailing pole tip in generator and leading pole tip in motor.

Now the machine has two fluxes, i.

At heavy loads, the cross magnetizing armature reaction may cause very high flux density in the trailing pole tip in generator action and leading pole tip in the motor action. There is an axis or, you may say, a plane along which reactuon conductors move parallel to the flux lines and, hence, they do not cut the flux lines while on that plane.