Brushes in a DC generator must be positioned in the neutral plane to avoid excessive sparking associated with the brushes. What device is used to prevent the shifting of the neutral plane due to armature reaction for varying generator loads.

Correct Answer: Option D — commutating pole windings

Commutating pole windings, or interpoles, produce a magnetic flux that opposes armature reaction across varying generator loads. According to IEEE 45 and 46 CFR Subchapter J principles, this maintains the neutral plane automatically, preventing destructive brush sparking without requiring manual shifting of the brush rigging.