The correct answer is: A. Providing laminations in armature core
Hysteresis loss is a type of energy loss that occurs in a magnetic material when it is subjected to an alternating magnetic field. The loss occurs due to the movement of magnetic domains within the material as the field changes. The amount of hysteresis loss is proportional to the square of the magnetic flux density.
Laminations are thin sheets of magnetic material that are stacked together to form the armature core of a DC generator. The laminations are insulated from each other by a thin layer of varnish or lacquer. This insulation prevents the magnetic domains from moving from one lamination to another, which reduces the hysteresis loss.
The other options are not likely to result in a reduction of hysteresis loss. Providing laminations in the stator will not affect the hysteresis loss in the armature core. Using a nonmagnetic material for the frame will not affect the hysteresis loss in the armature core. Using a material of low hysteresis coefficient for the armature core material will reduce the hysteresis loss, but this is not the most effective way to reduce the loss.
In conclusion, the correct answer is: A. Providing laminations in armature core