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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The following figure shows: The effect of the armature field is to distort the generator field and shift the neutral plane. 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. When the field flux enters into the armature, they atmature get distorted. Fitzgerald, Charles Kingsley, Jr. This is because the direction of armature reaction mmf is in the inter polar axis.
Windings are held in slots in the rotor or armature covered by stator magnets. Compensating winding functions satisfactorily irrespective of the load, direction of rotation and mode of operation. 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.
Armature Reaction in DC Machine
Thus in this case compensation windings are installed in slots of the poles faces of main field poles. So, the neutral zone can set at orthogonal to the main flux. This results an armature current flux directed along the brush axis and causes cross magnetization of the main field. Overall flux is less than the field flux because saturation occur at the pole armatire B of the field pole due to higher field flux, thus increase in the flux at pole tip B reactkon less than the decrease in the flux at pole tip A.
And the direction of flux generates in the conductors is given by the cork-screw rule. Armature reaction is essential in amplidyne rotating amplifiers. Brush shift has serious limitations, so the brushes have to be shifted to a new position every time the load changes or the direction of rotation changes armatre the mode of operation changes.
This will reduce the induced voltage in generator and would increase the speed in motor. The MNA is continuously shifted with the resultant flux. The direction of rotation is consider as anti-clockwise. 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. This happens when machines running at no load condition.
Armature Reaction in DC Machine
This cross magnetization effect results in the concentration of flux at the trailing pole tip in generator action and at the leading pole tip in motor action.
The brushes of the DC machines are always placed in this axis, and hence this axis is called the axis of commutation. Coilgun Railgun Superconducting machine. 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 aarmature direction of current in the armature conductors under that pole arc.
In other projects Wikimedia Commons. When no load connected to the generator, the armature current becomes zero. Alternator Electric generator Inchworm motor. Recieve free updates Via Email!
Why not share it? The armature flux superimposes with the main field flux and, hence, disturbs the main field flux as shown in third figure the of above image. So this amplitude keeps varying then the resultant could be armatufe any direction depending upon the amount of load current as shown in Fig. 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 this flux.
What is Leading and Trailing Pole tip? Click here to sign up. Inter poles are long but narrow poles placed in the inter polar axis. The distortion increases the density of the flux in the upper pole tip of N-pole and the lower pole tip of the south pole. Due to motion of coil, current induced in the conductors of the coil which flow through the brushes and to the external circuit. And the negative terminal brush is connected to winding which is wound over There are many problems like high circulating current, poor this small pole and it is connected to negative rdaction.