The Revolution of Induction Motors: Nikola Tesla’s Enduring Legacy
Nikola Tesla’s Invention that Shaped the World
The invention of Induction Motors permanently altered the course of human civilization.
This hundred-year-old motor, invented by the great scientist Nikola Tesla, remains the most common motor type even today. In fact, approximately 50% of global electric power consumption is due to induction motors.
Let’s delve into the inner workings of induction motors and explore the genius thinking of Nikola Tesla.
Understanding the Induction Motor
The induction motor comprises two main components: the stator and rotor.
The stator consists of a three-coil winding, and a three-phase AC power input is supplied to it. These windings pass through slots in the stator, formed by stacking thin, highly permeable steel laminations within a steel or cast iron frame.
When a three-phase current flows through these windings, something remarkable occurs — it generates a rotating magnetic field (RMF).
This RMF is the driving force behind the rotor’s motion.
The Rotating Magnetic Field
To comprehend how the rotating magnetic field is generated and its properties, consider a simplified stator winding.
In this arrangement, the three coils are connected 120º apart, and a wire carrying current produces a magnetic field around it. When a three-phase power is applied to this special arrangement, the magnetic field produced varies with time.
Comparing these three instances, it’s akin to a magnetic field of uniform strength rotating. This rotational speed is known as the synchronous speed.
If you introduce a closed conductor within this rotating field, Faraday’s law tells us that an electromotive force (EMF) will be induced in the loop, creating a current. According to the Lorentz Force law, an electromagnetic force will act on the loop, causing it to rotate.
This same phenomenon occurs inside an induction motor. Instead of a simple loop, a structure similar to a squirrel cage is employed. The three-phase AC current passing through the stator produces a rotating magnetic field, inducing current in the bars of the squirrel cage, which are shorted by end rings.
Consequently, the rotor begins to rotate. This unique feature distinguishes the induction motor as electricity is induced on the rotor through electromagnetic induction, rather than a direct connection.
To facilitate electromagnetic induction, insulated iron core laminations are packed inside the rotor. These small iron laminations minimize Eddy current losses.
Self-Starting Advantage
One of the most significant advantages of the induction motor is its inherent self-starting capability. Both the magnetic field and the rotor are in rotation.
However, the rotor cannot catch up to the speed of the magnetic field. It rotates at a specific speed slightly less than the synchronous speed.
The difference between the synchronous and rotor speeds is known as “slip.”
Induction Motors: The Preferred Choice
Now, let’s explore why induction motors dominate both industrial and domestic applications:
- No Permanent Magnet or Brushes: Induction motors do not require permanent magnets, brushes, commutator rings, or position sensors, setting them apart from other electrical machine counterparts.
- Self-Starting: As mentioned earlier, induction motors have the remarkable ability to self-start, eliminating the need for external mechanisms.
- Speed Control: Controlling the speed of induction motors is remarkably straightforward. By adjusting the input power frequency using a variable frequency drive, the motor’s speed can be easily regulated.
These properties make induction motors an attractive choice for various applications, including elevators, cranes, and even electric cars.
The high-speed band of induction motors enables electric cars to operate with a single-speed transmission, enhancing their efficiency.
Another intriguing aspect of induction motors is their capacity to act as generators when the rotor is set in motion by a prime mover.
In such cases, it’s crucial to ensure that the RMF speed is always less than the rotor speed.
In Conclusion
In summary, you now have a clear understanding of the ingenious operating principles behind an induction motor and why it continues to reign supreme in both domestic and industrial domains.
Nikola Tesla’s pioneering work has left an indelible mark on the world, and the induction motor remains a testament to his brilliance.
