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Since the armature reaction increases when the armature load current increases, and the effect of the commutating poles (Interpoles) also increases, the result is that the neutral or commutating plane is maintained in a fixed position throughout the load range. Most of the armature current goes through the commutating pole windings only a small amount goes through the shunting resistor. A resistor connected in parallel with the commutating pole (Interpole) windings is adjusted and permanently set at the factory to give the commutating pole strength that results in the best commutation.
#Dc motor winding series
The commutating pole (Interpole) windings are all connected in series with each other and with the armature circuit. The amount of shift caused by the interpoles will equal the shift caused by armature reaction since both shifts are a result of armature current.
![dc motor winding dc motor winding](https://5.imimg.com/data5/TA/XX/SR/SELLER-8163267/ro-pump-armature-500x500.jpg)
This field, in effect, cancels the armature reaction for all values of load current by causing a shift in the neutral plane opposite to the shift caused by armature reaction. The field generated by the interpoles produces the same effect as the compensating winding. Interpoles are wound and placed so that each interpole has the same magnetic polarity as the main pole ahead of it, in the direction of rotation. The commutating field, or interpoles, as they are sometimes called because of their position relative to the main poles, consist of a series of small poles similar to the main field poles in construction and method of fastening, but having a winding that consists of a few turns of heavy copper bus bar of high current capacity and low resistance. The interpoles have a few turns of large wire and are connected in series with the armature. Read: Construction of DC Machines Interpole (Commutator Field Winding)Īnother way to reduce the effects of armature reaction is to place small auxiliary poles called “interpoles” between the main field poles.
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Good commutation is thus affected with the brushes located in a fixed position. Thus it is ensured that the neutral plane will remain in a fixed position throughout the entire range of load and speed of the machine, and, in the ease of a motor, in both directions of rotation. The effect of the two windings acting in conjunction is to neutralize completely the effects of armature reaction in respect to the shifting of the neutral plane and to eliminate almost completely the distorting effects. The field resulting from the compensating windings is wide in comparison with the commutating fields but weaker since the flux is less concentrated. The current in them is then equal to that in the armature. The compensating windings are connected in series with each other and with the armature winding in a manner similar to the interpole windings so that they also oppose the field set up by armature reaction. Compensating winding in a large dc machineĬompensation windings consist of a few turns of low-resistance copper bar laid in slots in the faces of the main shunt field pole pieces and so connected that the windings carry current in the reverse direction to that of the immediately adjacent armature conductors. To neutralize completely the effects of armature reaction, a second set of auxiliary field windings, known as the compensating windings, is used in high-power d.c. Because of this, once the brushes have been set correctly, they do not have to be moved again. The neutral plane will remain stationary and in its original position for all values of armature current. Because the compensating windings are wound to produce a field that opposes the magnetic field of the armature, they tend to cancel the cross magnetizing effect of the armature magnetic field. The series-connected compensating windings produce a magnetic field, which varies directly with armature current. Compensating Windings and Interpoles in dc machine These coils are connected in series with the armature. The compensating windings consist of a series of coils embedded in slots in the pole faces. In order to neutralize the cross magnetizing effect of armature reaction, a compensating winding is used. machines subjected to large fluctuations in load. The cross-magnetizing effect of armature reaction may cause trouble in d.c.