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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In a “lap” winding, there are as many current paths between the brush or line connections as there are poles in the field winding. They have the polarity of succeeding pole coming next in sequence of rotation in generator action and proceeding which has passed behind in rotation sequence pole in motor action. Armature reaction also comes in the way of good commutation. Larger generators require the use of interpoles.

The content on this website is copyrighted and may not be reproduced. 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. The word armature was first used in its electrical sense, i. Leave a Reply Cancel reply Your email address will not be published. The cross magnetizing armature reaction effect is mainly caused by armature conductors which are located under the pole arc.

This mutual action of armature flux on the main field flux is known as armature reaction.

The effect of the armature field is to distort the generator field and shift the neutral plane. In a DC machine, two sources of magnetic fluxes are present; ‘armature flux’ and ‘main field flux’. The north-south poles and conductors are in circular armature.

This effect is called as armature reaction in DC machines.

Armature Reaction in DC machines

In view of this, brush shift is limited only to very small machines. In an induction generatorgenerated power is drawn from the stator. Thus in this case compensation windings are installed in slots of the poles faces of main field poles. Because the load current is varying quantity which means the flux due to armature current which indicating orthogonal to the north-south flux the amplitude keeps varying.

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This happens when machines running at no load condition. This can be achieved by installing commutating poles in between two consecutive main poles. Consequently, the coil under this tip may develop induced voltage high enough to cause a flash over between the associated adjacent commutator segments particularly, because this coil is physically close to the commutation zone at the brushes where the air temperature might be already high due to commutation process.

Armature (electrical) – Wikipedia

Inter Pole The limitation of brush shift has led to the use of inter poles in almost all the medium and large sized DC machines. Log In Sign Up. Fig 3 Lorentz force law So the field on the bottom side of the conductor is tried to oppose the main field and field becomes weak while ar,ature Fig 1 a Magnetic Flux lines of north-south kn, upper field becomes stronger because of adding.

Due to motion of coil, current induced in the conductors of the coil which flow geaction the brushes and to the external circuit. So, due to these problems like circulating current which itself heat up the winding and the other one is 3. 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.

Compensating windings major d.c.mwchines So, for a given rating of machine, a wave winding is more suitable for large currents and low voltages. Thus, no sparking takes place.

Leave a comment Click here to cancel reply. The direction of current remains same in all the conductors which lying under one pole. The armathre neutral axis or plane is perpendicular to the axis of the magnetic flux. The effect of armature flux on the main field flux is called “armature reaction”.

Views Read Edit View history. 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 d.c.macgines the trailing tip.

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Armature Reaction in DC Machine

Armature reaction causes the neutral plane to shift in the direction of rotation, and if the brushes are in the neutral plane at no load, that is, when no armature current is flowing, they will not be in the neutral plane when armature current is flowing. This phenomenon is thus known as the demagnetizing effect of cross magnetizing armature reaction, which is further compensated by the use of compensating windings.

Circuit Globe All geaction Electrical and Electronics. If the load varies to a marked degree, the neutral plane will shift proportionately, and the brushes will not be the correct position at all times.

The first is to carry current crossing the field, thus creating shaft torque in a rotating machine or force in a linear machine. This may cause confusion when working with compound machines like brushless alternators, or in conversation among people who are accustomed to work with differently configured machinery. Brush shift has serious limitations, so the brushes have d.c.machiines be shifted to a new position every time the load changes or the direction of rotation changes or the mode of operation changes.

The conductor on the right-hand sides is also combining their MMF for producing the flux in the downwards direction. When no load connected to the generator, reacrion armature current becomes zero. Consider the condition in which only the armature conductors carrying current and no current flows through their main poles. For this reason it is desirable to incorporate a corrective system into the generator design.

In a DC machinetwo kinds of magnetic fluxes are present; ‘armature flux’ and ‘main field flux’. As armature reaction effects are not good for normal operation of DC Machine both generator and motor. Now, the In D.

AC motor DC motor.

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