Following energized winding of a D.C. machine should not be opened as it would produce high inductive voltage which may be dangerous to personnel and may cause its own insulation failure.

The correct answer is: D. Shunt field

A shunt field is a winding that is connected in parallel with the armature of a DC motor. When the shunt field is energized, it creates a magnetic field that interacts with the magnetic field created by the armature. This interaction produces a torque that causes the motor to rotate.

If the shunt field is opened while the motor is running, the magnetic field will collapse rapidly. This collapse of the magnetic field will induce a high voltage in the armature windings. This high voltage can be dangerous to personnel and may cause the insulation of the armature windings to fail.

The other options are incorrect because they are not windings that are connected in parallel with the armature.

• The series field is a winding that is connected in series with the armature.
• The compensating field is a winding that is used to reduce the armature reaction.
• The inter pole field is a winding that is located between the main poles of a DC motor.