The correct answer is: A. It cannot be reversed, ordinarily.
A reluctance motor is a type of electric motor that uses the principle of reluctance to produce torque. Reluctance is the opposition to the flow of magnetic flux. The rotor of a reluctance motor is made up of a number of poles that are arranged in a non-symmetrical pattern. This arrangement causes the rotor to have a higher reluctance to magnetic flux in one direction than in the other. When a voltage is applied to the stator windings, a magnetic field is created. This magnetic field interacts with the rotor poles, causing the rotor to turn.
The direction of rotation of a reluctance motor can be changed by reversing the polarity of the voltage applied to the stator windings. However, this can only be done if the motor is stopped. Once the motor is up to speed, it will continue to rotate in the same direction, even if the polarity of the voltage is reversed.
The other options are all correct.
Option B: It requires no D.C. field excitation for its operation. This is because the rotor of a reluctance motor is made of a ferromagnetic material, which means that it can be magnetized by an external magnetic field. The stator windings of a reluctance motor are energized with an alternating current, which creates a rotating magnetic field. This rotating magnetic field induces an emf in the rotor, which causes the rotor to turn.
Option C: It is nothing else but a single-phase, salient pole synchronous-induction motor. This is not quite correct. A reluctance motor is similar to a synchronous motor in that both motors have a stator with windings and a rotor that is made of a ferromagnetic material. However, a synchronous motor has a DC field winding in the rotor, while a reluctance motor does not. This difference in construction means that a reluctance motor cannot operate at synchronous speed.
Option D: Its squirrel cage-rotor is of unsym-metrical magnetic construction in order to vary reluc-tance path between stator and rotor. This is correct. The rotor of a reluctance motor is made up of a number of poles that are arranged in a non-symmetrical pattern. This arrangement causes the rotor to have a higher reluctance to magnetic flux in one direction than in the other. This difference in reluctance causes the rotor to turn.