Which of the following is NOT a purpose of interpoles in a generator?

Interpoles, or compoles, are used in generators primarily to improve performance by addressing specific issues related to armature reaction and maintaining effective commutation. The correct answer relates to the fact that reducing armature reaction is one of the primary purposes of interpoles.

Using interpoles enhances the alignment of the magnetic field produced by the winding with the armature field, which leads to improved commutation. This function allows for smoother brush operation and aids in maintaining the voltage output by keeping the electromagnetic forces more stable under load conditions. Additionally, interpoles play a vital role in reducing sparking at the brushes by ensuring that the voltage induced in the armature windings remains balanced during operation, facilitating a cleaner commutation process.

The other options include enhancing voltage output and mitigating sparking, both relevant benefits of interpole implementation. However, the option involving reducing field strength does not correspond to the function of interpoles. Instead, interpoles help maintain the necessary magnetic field strength for accurate operation rather than reducing it. Thus, the statement that reducing armature reaction is NOT a purpose of interpoles is incorrect, making that a suitable choice for the question.