Synchronous Motor vs Asynchronous Motor | Synchronous vs Induction Motor | Come4Concepts

Summary

In this video, we explore the key differences between synchronous and induction motors. Synchronous motors operate at a constant speed, while induction motors run at a speed slightly lower than their synchronous speed. The video compares the construction, working principles, and efficiency of both motors, highlighting differences in rotor designs, excitation methods, and power factor control. Synchronous motors are more efficient and versatile, used for power factor improvement, whereas induction motors are simpler and self-starting. The video also touches on the maintenance, cost, and hunting phenomena in both motor types, providing a comprehensive overview of these AC machines.

Takeaways

• 😀 Synchronous motors run at a constant speed, while induction motors run at a speed slightly less than the synchronous speed.
• 😀 The stators of both synchronous and induction motors are similar, with three-phase windings located in specific slots.
• 😀 Induction motors have two types of rotors: squirrel cage rotors (which cannot add external resistance) and wound rotors (which allow for added resistance to improve starting torque).
• 😀 The rotor of a synchronous motor is excited by a separate DC source, while the rotor of an induction motor is not externally excited.
• 😀 Induction motors operate based on Faraday's Law of Electromagnetic Induction, where a rotating magnetic field induces current in the rotor, causing rotation.
• 😀 Synchronous motors require an external prime mover to start, as they need to reach synchronous speed before they can operate, whereas induction motors start immediately upon supplying power.
• 😀 The slip between the rotating magnetic field and the rotor is necessary for the operation of an induction motor, while synchronous motors have zero slip as the rotor and stator rotate in sync.
• 😀 Synchronous motors can operate at any power factor by adjusting their field excitation, whereas induction motors always operate at a lagging power factor.
• 😀 Synchronous motors are generally more efficient than induction motors of the same output, due to their ability to adjust the power factor.
• 😀 Induction motors are widely used for driving mechanical loads, while synchronous motors can also be used for power factor improvement in addition to driving loads.

Q & A

What is the main difference between a synchronous motor and an induction motor?

The primary difference is that a synchronous motor runs at a constant speed, while an induction motor runs at a speed slightly less than synchronous speed.

How does the stator of an induction motor differ from that of a synchronous motor?

The stator of both motors is similar, as both have three-phase windings located in the stator core. However, the rotor construction is different in each motor, with induction motors having either squirrel-cage or wound rotors, while synchronous motors have rotors excited by a DC supply.

What is the purpose of the squirrel-cage rotor in an induction motor?

The squirrel-cage rotor consists of laminated cylindrical cores with rotor bars connected to end rings. It is designed for simple construction and operation. It cannot have external resistance added, which limits its starting torque.

What is the difference between a squirrel-cage rotor and a wound rotor in an induction motor?

A squirrel-cage rotor does not allow the addition of external resistance, whereas a wound rotor enables external resistance to be added, improving the starting torque of the motor.

How does a synchronous motor maintain a constant speed?

A synchronous motor maintains a constant speed because its rotor is made to rotate at a synchronous speed, which is achieved through an external prime mover. This ensures the rotor remains magnetically locked with the stator's rotating magnetic field.

What is the principle of operation of an induction motor?

An induction motor works on Faraday's law of electromagnetic induction. When a three-phase AC supply is given to the stator, it produces a rotating magnetic field. This field induces an electromotive force (EMF) in the rotor, causing it to rotate.

Why is a synchronous motor considered a doubly excited machine?

A synchronous motor is considered doubly excited because its stator is supplied with a three-phase AC supply, and its rotor is excited by a separate DC source to generate a magnetic field.

What is the hunting effect in synchronous motors, and how does it affect performance?

Hunting occurs when the synchronous motor's rotor cannot stabilize at its equilibrium position due to inertia, often caused by sudden changes in load or speed. It is undesirable as it impacts the motor's performance and can cause instability.

What are the advantages of using a synchronous motor over an induction motor?

Synchronous motors can operate at any power factor, offering greater efficiency and flexibility compared to induction motors. Additionally, they can be used for power factor improvement, whereas induction motors always operate at a lagging power factor.

Why do synchronous motors require external starting mechanisms?

Synchronous motors require external starting mechanisms because they do not have high starting torque. The rotor must be brought up to synchronous speed using an external prime mover, unlike induction motors which can start by simply applying a three-phase AC supply.