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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So it rotates with same rpm and as a result getting the same induced emf [1] [2] [3]. The first method is to shift the position of the brushes so that they are in the neutral plane when the generator is producing its normal load current.

Similarly, the right-hand side conductors carry current, and their direction goes out of the paper shown by dots inside the circle. Obviously it is help in commutation as the inter polar winding gets relieved from its duty to compensate for the armature mmf under the pole arc. This means the flux d.c.machinez to armature current or in fact the armature reaction is now zero. But, due to current flowing in the conductor of coil, there will be a field around it, now this field is going to interact with the main flux field of the north south magnetic poles which has been applied.

The direction of rotation is consider as anti-clockwise. armaturw

In no load condition, the magnetic neutral axis coincides with the geometrical neutral axis. Copper armature wiring enhances electrical efficiencies due to its higher electrical conductivity. This happens when machines running at no load condition.

Armature Reaction in DC Machine

The neutral plane is the position where the armature windings are moving parallel to the magnetic flux lines, that is why an axis lying in this plane is called as magnetic neutral axis MNA. Compensating Winding Commutation problem is not the only problem in DC machines. Electromagnetic components Electric motors.

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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.

These windings are connected in series with the armature winding in such a position that the current flowing in the compensation winding is exactly opposite to the current flowing in the armature winding at the same time. Compensating winding consists of conductors embedded in the pole face that run parallel to the shaft and carry an armature current in a direction opposite to the direction of current in the armature conductors under that pole arc.

With complete compensation the main field is restored. Due to current the comes out to electrical domain. There is an axis or, you may say, a plane along which armature conductors move parallel to the flux lines and, hence, they do not cut the flux lines while on that plane.

In a DC machine, two sources of magnetic fluxes are present; ‘armature flux’ and ‘main field flux’. Timeline of the electric motor Ball bearing motor Barlow’s wheel Lynch motor Mendocino motor Mouse mill motor. Similarly, the density of flux decreases in the lower pole tip of the north pole and the upper pole tip of the south pole.

The effect of the armature field is to distort the generator field and shift the neutral plane. If the motion is reversed in case of generatorthe tips is interchanged.

The resultant flux induces in the generator are shifted towards the direction of the rotation of generator. The armature flux is produced by the current induces in the armature conductors while the field pole flux is induced because of the main field poles. The parts of an alternator or related equipment can be expressed in either mechanical terms or electrical terms.

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The field this comes out as the induced voltage. Now, the In D. Since inter poles are connected in series with armature, the change in direction of current in armature changes direction of inter pole.

Larger generators require the use of interpoles. So, the neutral zone has much higher band of angle in which it can exist at various load current. Rection the brushes were contacting commutator segments outside the neutral plane, they would short-circuit “live” coils and cause arcing and loss of power. Your email address will not be published. In large machines subject to heavy overloads or plugging In small motors subject to sudden reversal and high acceleration.

This armature flux weakens and distort the main flux, thus the overall effective flux in Reacrion Generator decrease.

Armature Reaction in a DC Generator

Brushes are always placed along the MNA because reversal of current in the armature conductors takes place along this axis. Direction of load current equivalent flux in this direction which is shown in Fig. This is because commutation occurs at 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 d.c.machlnes. Fig 11 Commutating poles to reduced armature reaction Let the commutator which d.c.macyines placed and also have the brushes in the neutral zone.

Armature reaction in DC Generator

Field created by conductor will distort the main field. So neutral zone has shifted in the direction of rotation therefore brushes has been place in this new neutral zone. The brush-setting method is the most common means of correcting for armature reaction in small generators those producing approximately W or less.