Why Induction Motor cannot run at Synchronous Speed?

Why Induction Motor cannot run at synchronous speed?

An induction motor is designed to operate at a speed that is slightly less than the synchronous speed of the motor. The synchronous speed of an induction motor is determined by the frequency of the power supply and the number of poles in the motor. The synchronous speed can be calculated using the formula:

Synchronous Speed = (120 x Frequency) / Number of Poles

When an induction motor is connected to a power supply and the rotor is at standstill, the motor operates at a speed that is less than the synchronous speed. This is because the rotor has to slip in order to create the necessary magnetic field to induce the current in the rotor windings.

If the rotor were to operate at synchronous speed, there would be no relative motion between the magnetic field of the stator and the rotor, and therefore no induced current in the rotor. As a result, there would be no torque generated, and the motor would not be able to start or run.

In summary, an induction motor cannot run at synchronous speed because it requires relative motion between the magnetic field of the stator and the rotor to induce current in the rotor windings, and generate the necessary torque to start and run the motor.

What is Induction Motor?

An induction motor is an electric motor that operates based on the principles of electromagnetic induction. It is one of the most commonly used types of electric motor, with applications in a wide range of industries including manufacturing, transportation, and household appliances.

The basic design of an induction motor consists of a stator (stationary part) and a rotor (rotating part). The stator contains a series of windings that are supplied with AC power from an external source. This AC power creates a magnetic field in the stator windings, which rotates around the circumference of the stator.

The rotor is a cylindrical iron core with conductive bars, also known as "squirrel cages," mounted on its surface. When the stator magnetic field rotates, it induces an electromotive force (EMF) in the rotor bars, which in turn creates a magnetic field in the rotor. This interaction between the stator and rotor magnetic fields generates torque, causing the rotor to spin and ultimately power the load.

Unlike other types of electric motors, induction motors do not require brushes or commutators to transfer power from the stator to the rotor, which makes them simple, robust, and low-maintenance. Additionally, induction motors are highly efficient and can be designed to operate at a wide range of speeds, depending on the specific application requirements.

What is synchronous speed?

Synchronous speed is the speed at which the magnetic field generated by the stator of an AC electric motor rotates. It is determined by the frequency of the power supply and the number of poles in the motor, and is a function of the physical dimensions and design of the motor.

The synchronous speed of an AC motor can be calculated using the following formula:

Synchronous Speed = (120 x Frequency) / Number of Poles

where "Frequency" is the frequency of the AC power supply in hertz, and "Number of Poles" is the number of magnetic poles in the motor.

It is important to note that the actual operating speed of an AC motor is typically lower than the synchronous speed due to the presence of rotor slip, which is the difference between the synchronous speed and the actual operating speed of the rotor. The amount of slip is influenced by the load on the motor and varies with the specific motor design and operating conditions.

What is the slip of the Induction Motor?

The slip of an induction motor is the difference between the synchronous speed of the rotating magnetic field in the stator and the actual rotational speed of the rotor. In other words, it is the amount of "slippage" that occurs between the rotating magnetic field of the stator and the rotor, which is necessary for the induction motor to generate torque and operate.

The slip of an induction motor is expressed as a percentage, and can be calculated using the following formula:

Slip (%) = [(Synchronous Speed - Actual Rotor Speed) / Synchronous Speed] x 100

For example, if the synchronous speed of an induction motor is 1800 RPM (revolutions per minute), and the actual speed of the rotor is measured at 1750 RPM, the slip would be:

Slip (%) = [(1800 - 1750) / 1800] x 100 = 2.78%

The amount of slip in an induction motor is influenced by factors such as the motor's design, the load on the motor, and the frequency of the power supply. Typically, the higher the load on the motor, the greater the slip, which in turn leads to a reduction in the motor's efficiency.

 Synchronous speed of Induction Motor Formula

The synchronous speed of an induction motor can be calculated using the following formula:

Synchronous Speed = (120 x Frequency) / Number of Poles

where:

• "Frequency" is the frequency of the AC power supply in hertz (Hz)
• "Number of Poles" is the number of magnetic poles in the motor

For example, consider an induction motor with a power supply frequency of 60 Hz and 4 poles. Using the formula, we can calculate the synchronous speed as:

Synchronous Speed = (120 x 60) / 4 = 1800 RPM

This means that in this example, the rotating magnetic field generated by the stator of the induction motor will rotate at a speed of 1800 revolutions per minute, assuming no load or slip on the motor. However, the actual operating speed of the rotor will be less than the synchronous speed due to the presence of slip. 

what is synchronous speed in induction motor

In an induction motor, synchronous speed refers to the speed at which the rotating magnetic field generated by the stator of the motor rotates. It is determined by the frequency of the AC power supply and the number of magnetic poles in the motor.

The formula to calculate the synchronous speed of an induction motor is:

Synchronous Speed = (120 x Frequency) / Number of Poles

where:

• "Frequency" is the frequency of the AC power supply in hertz (Hz)
• "Number of Poles" is the number of magnetic poles in the motor

For example, if an induction motor is connected to a power supply with a frequency of 60 Hz and has 4 poles, the synchronous speed can be calculated as:

Synchronous Speed = (120 x 60) / 4 = 1800 RPM

This means that in this example, the rotating magnetic field generated by the stator of the induction motor will rotate at a speed of 1800 revolutions per minute. However, the actual operating speed of the rotor will be less than the synchronous speed due to the presence of slip.

Read More: What is Induction Motor? How many types of Induction Motor and what are they? Detailed Discussion about Induction Motor