Differences between Induction and Synchronous Motors

Both induction and synchronous motors are 3-phase AC motors, but they have several key differences in their operation and characteristics.

Induction motors: The rotor of an induction motor can be either a squirrel cage type or a wound type. Both types have a winding but in a wound rotor, the winding terminates in slip rings and external connections. In contrast to synchronous motors, the rotor of an induction motor does not require a separate DC excitation. Instead, the rotor currents are induced by the rotating magnetic field produced by the stator winding.
Synchronous motors: The rotor of a synchronous motor typically has salient poles with windings that require a separate DC excitation source. This DC excitation creates a magnetic field on the rotor that interacts with the rotating magnetic field produced by the stator.

Induction motors: Induction motors are self-starting due to the interaction of the rotating magnetic field with the rotor conductors, which induces currents and produces torque. The starting torque can be enhanced in some types of induction motors, such as double-cage motors.
Synchronous motors: Synchronous motors are *not self-starting. To start a synchronous motor, an auxiliary means is required, such as a *damper winding (squirrel cage winding on the rotor) or a separate starting motor. The damper winding allows the motor to start as an induction motor, and once it reaches near synchronous speed, the rotor is excited with DC current, causing it to lock in with the rotating magnetic field and run at synchronous speed.

Induction motors: The speed of an induction motor is slightly less than synchronous speed and *varies with the load. The difference between the synchronous speed and the actual rotor speed is called *slip, which is necessary for torque production.
Synchronous motors: A synchronous motor runs at synchronous speed (Ns = 120f/P) under all load conditions. The speed is constant and determined by the frequency of the AC supply and the number of poles.

Induction motors: Induction motors inherently operate at a lagging power factor because they draw reactive power from the supply to establish the magnetic field.
Synchronous motors: Synchronous motors offer the unique advantage of power factor control. By adjusting the field excitation, the power factor can be varied from lagging to leading. When over-excited, a synchronous motor can even supply reactive power to the system, acting like a capacitor and improving the overall power factor of the system. This ability to operate at a leading power factor makes synchronous motors valuable for power factor correction in industrial settings.

Induction motors: Induction motors are widely used in various applications due to their simplicity, robustness, and self-starting capabilities. They are commonly found in pumps, fans, compressors, conveyors, and many other industrial machines.
Synchronous motors: Synchronous motors are preferred in applications where constant speed is critical, such as in clocks, timers, and precision equipment. They are also used in power factor correction and as synchronous condensers to improve the overall power factor of a system

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