Introduction:
In electrical engineering, there are several types of alternating current (a.c.) motors. Some of these motors are synchronous type, which means that the rotor rotates at the same speed as the rotating magnetic field produced by the stator. This synchronization is achieved through various mechanisms. In this explanation, we will discuss the types of a.c. motors that are synchronous in nature.

Types of Synchronous A.C. Motors:

1. Universal Motor:
A universal motor is a type of motor that can run on either direct current (D.C.) or alternating current (A.C.). It is a synchronous motor because the rotational speed of the rotor is synchronized with the frequency of the applied voltage. The universal motor is commonly used in household appliances, such as vacuum cleaners and power tools, due to its ability to operate on both D.C. and A.C. power sources.

2. Reluctance Motor:
A reluctance motor is a type of synchronous motor where torque is developed due to the tendency of the rotor to align itself in the minimum reluctance position with respect to the stator field. The rotor of a reluctance motor has salient poles, and the magnetic reluctance of the rotor is varied by changing the position of the rotor with respect to the stator field. This variation in reluctance creates a torque that makes the rotor rotate at synchronous speed.

3. Hysteresis Motor:
A hysteresis motor is another type of synchronous motor where the rotor is made of a ferromagnetic material with high hysteresis loss. The rotor is magnetically coupled to the stator, and when an alternating current is applied to the stator, the magnetic field rotates. The hysteresis loss in the rotor material causes the rotor to rotate at the same speed as the rotating magnetic field, making it a synchronous motor.

Conclusion:
In summary, both the reluctance motor and the hysteresis motor are types of synchronous a.c. motors. These motors operate at the same speed as the rotating magnetic field produced by the stator. The universal motor is also a synchronous motor, as its rotor speed is synchronized with the frequency of the applied voltage.