The following constitute short-circuit in the armature winding.

The correct answer is: D. All of the above.

A short circuit in the armature winding is a fault condition that occurs when there is a direct connection between two or more points in the armature winding that are not supposed to be connected. This can happen due to insulation failure between two commutator bars, insulation failure between two turns of a coil, or two or more turns of the same coil getting grounded.

When a short circuit occurs, it causes a large current to flow through the armature winding. This can damage the winding and the commutator, and can also cause the motor to overheat. In some cases, a short circuit can even cause the motor to catch fire.

If you suspect that there is a short circuit in the armature winding of your motor, you should have it inspected by a qualified technician. Do not attempt to repair the motor yourself, as this could be dangerous.

Here is a more detailed explanation of each of the options:

• Option A: Insulation failure between two commutator bars. The commutator is a cylindrical metal ring that is divided into a number of segments. The armature winding is connected to these segments. If the insulation between two commutator bars fails, the current can flow directly from one bar to the other. This can cause a short circuit.
• Option B: Insulation failure between two turns of a coil. The armature winding is made up of a number of coils. Each coil is made up of a number of turns of wire. If the insulation between two turns of a coil fails, the current can flow directly from one turn to the other. This can cause a short circuit.
• Option C: Two of more turns of the same coil getting grounded. The armature winding is insulated from the stator. If the insulation between two turns of a coil fails, and the turns come into contact with the stator, the current can flow directly from the turns to the stator. This can cause a short circuit.

As you can see, all of the options listed in the question can cause a short circuit in the armature winding. If you suspect that there is a short circuit in the armature winding of your motor, you should have it inspected by a qualified technician.