Consider the following statements:The use of interpoles in dc machines...
In practice, the interpoles of appropriate polarity are strengthened so that in interpolar zone, the armature cross flux is neutralized and in addition some flux is produced there. This additional flux in the interpolar zone induces rotational emf in the commutated coil in such a direction as to oppose the reactance voltage. So, the resultant emf in the commutated coil would be zero and therefore zero current in that coil would amount to sparkless commutation. This is the reason why interpoles are designed to provide more mmf than the armature mmf in the commutating zone. In practice, the interpole mmf may be 1.2 to 1.3 times the armature mmf per pole.
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Consider the following statements:The use of interpoles in dc machines...
Interpoles in DC Machines
Interpoles are additional poles that are placed between the main poles of a DC machine. They are used to improve the commutation process by counteracting certain effects that occur during operation. Let's analyze each statement and determine their accuracy.
Statement 1: The use of interpoles in DC machines is to counteract the reactance voltage.
This statement is incorrect. The reactance voltage is a result of the inductance of the armature windings and the current flowing through them. Interpoles are not specifically designed to counteract reactance voltage. However, they do help in improving the commutation process, which indirectly affects the reactance voltage.
Statement 2: The use of interpoles in DC machines is to counteract the demagnetizing effect of armature mmf in the commutating zone.
This statement is correct. The commutating zone is the region where the brushes make contact with the commutator. In this region, the armature mmf (magnetomotive force) acts in a direction that opposes the main field produced by the main poles. This demagnetizing effect can cause poor commutation and sparking. Interpoles are designed to produce a mmf that counteracts this demagnetizing effect, ensuring better commutation.
Statement 3: The use of interpoles in DC machines is to counteract the cross-magnetizing effect of armature mmf in the commutating zone.
This statement is also correct. The armature mmf also produces a cross-magnetizing effect in the commutating zone. This effect creates an uneven distribution of the magnetic field, leading to poor commutation and sparking. Interpoles are designed to produce a mmf that counteracts this cross-magnetizing effect, ensuring better commutation.
Conclusion:
From the analysis above, we can conclude that statement 2 and 3 are correct. Interpoles in DC machines are specifically designed to counteract the demagnetizing effect and cross-magnetizing effect of the armature mmf in the commutating zone. They improve the commutation process and reduce sparking, resulting in better performance and efficiency of the DC machine.
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