The correct answer is: A. Series motor
A series motor has got maximum self loading property. This means that the torque of a series motor increases with the increase in load. This is because the field current and the armature current are in series in a series motor. So, when the load increases, the armature current increases, which in turn increases the field current. This increase in field current produces a stronger magnetic field, which produces a greater torque.
A shunt motor has got minimum self loading property. This means that the torque of a shunt motor is almost independent of the load. This is because the field current and the armature current are in parallel in a shunt motor. So, when the load increases, the armature current increases, but the field current remains almost constant. This is because the field winding is connected to a constant voltage source.
A cumulatively compounded motor has got more self loading property than a shunt motor, but less than a series motor. This is because the field current and the armature current are in series in a cumulatively compounded motor, but the field winding is also connected to a separate voltage source. So, when the load increases, the armature current increases, which in turn increases the field current. This increase in field current produces a stronger magnetic field, which produces a greater torque. However, the increase in field current is not as much as in a series motor, because the field winding is also connected to a separate voltage source.
A differentially compounded motor has got less self loading property than a shunt motor. This is because the field current and the armature current are in series in a differentially compounded motor, but the field winding is connected to a separate voltage source with the opposite polarity. So, when the load increases, the armature current increases, which in turn increases the field current. This increase in field current produces a weaker magnetic field, which produces a smaller torque.