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AC Motor: What Is It? How Does It Work? Types & Uses

Electric motors are used in almost every industry and in a wide range of applications. Electric motors are available in a wide range of sizes and types. These motors can be selected based on their functioning, voltage, and applications. Using the proper motor with high-quality parts and performing regular maintenance keeps your motor running smoothly and protects endpoint equipment from wear and power spikes. 

This article will teach you the fundamentals of AC motors, working,types, advantages & disadvantages in detail.

WHAT IS AN ELECTRIC MOTOR?

Electric motor is a machine which converts electrical energy into mechanical energy usually by employing electromagnetic phenomena. . It works on the principle that when a current-carrying conductor is placed in a magnetic field, it experiences a mechanical force whose magnitude is determined by F = BIl Newton and whose direction is determined by Fleming’s Left-hand Rule. 

The various types of electric motor differ in the ways in which the conductors and the field are arranged and also in the control that can be exercised over mechanical output torque, speed, and position. The following are the two main types of electric motors:

  • AC motors, which are powered by alternating current
  • DC motors, which are powered by direct current

AC MOTOR:

An alternating current is required for the AC motor to rotate. Using electromagnetic induction, this motor transforms alternating current to mechanical power. Magnetic fields generated by coils wrapped around the output shaft provide energy to an AC motor. AC motors are efficient, long-lasting, quiet, and adaptable, making them a suitable option for a variety of power generation applications.

The stator, or fixed outer drum, and the rotor, or revolving inner section coupled to the motor shaft, are the two primary components of an AC motor. Rotating magnetic fields are generated by the stator and rotor. The winding of the stator that creates the rotating field is created by alternating current.

When an AC supply flux is connected to the stator, an air gap is generated, which rotates the flux at a fixed synchronous speed, producing voltages in the stator and rotor winding.

Construction of an AC motor

An AC motor is powered by alternating current. AC motors are made up of two main components: a stationary stator and a rotating rotor. Let’s look at the various components of an AC motor in this section.

Stator

The stator is the motor’s stationary component that provides a revolving magnetic field to the rotor.

Stator Core

The stator core is made of thin metal sheets, which are known as laminations.  To prevent energy loss, laminations are employed.

Stator Windings

The windings of the stator are layered to form a hollow cylinder. Insulated wires are used in the slots of the stator core coils.

The stator windings are connected to a power supply when the assembled motor is turned on. When the current is supplied, each group of coils, combined with the steel core, creates an electromagnet.

Rotor

A rotor is a central component of a motor that is fixed to the shaft. The squirrel cage rotor is the most frequent form of rotor used in AC motors. A squirrel-cage rotor is a cylindrical rotor consisting of thin steel laminations stacked one on top of the other.

Instead of placing wire coils between the holes, conductor bars are die-cast into the cylinder’s evenly spaced slots. After die-casting, the conductor bars are electrically and physically linked to the end rings.

Motor Shaft

To form a rotor assembly, the rotor is pushed onto a steel shaft. The shaft extends outside the motor case, allowing for transmission of rotational power to an external system.

Bearings

The motor shaft is held in place by bearings. The bearings reduce the friction between the shaft and the casing, increasing the motor’s efficiency.

Enclosure

The enclosure keeps water and other external elements out of the motor’s interior components. A frame and two end brackets make up the enclosure.

Working Principle of an AC Motor

The fundamental operation of an AC Motor depends on the principle of magnetism. The simple AC Motor contains a coil of wire and two fixed magnets surrounding a shaft.  The coil of wire becomes an electromagnet when an electric (AC) charge is applied to it. A magnetic field is generated by this electromagnet.

A solid metal axle, a wire loop, a coil, a squirrel cage formed of metal bars, and some other freely revolving metal item that may conduct electricity are all found inside the stator. In an AC motor, power is delivered to the stator’s outer coils. The coils were energised in pairs, one after the other, creating a magnetic field that rotated around the motor’s outside.

Classification of AC Motor

Based on the principle of operation, AC motors are classified as:

  • Synchronous Motor
  • Induction Motor
  • Synchronous Motor
Synchronus motor

A motor that converts an AC electrical power into mechanical power and operates only at the synchronous speed is the synchronous motor.The stator in this motor features axial slots with stator winding wound for a certain number of poles. A Salient Pole Rotor is defined by the rotor winding that is mounted on it. Slip rings are used to feed a DC supply to the rotor winding. It’s also possible to employ a rotor with permanent magnets.

Sychronous ac motor construction

A revolving field is created when power is applied to a synchronous motor. This field tries to drag the rotor along with it, but it is unable to rotate due to rotor inertia. As a result, it does not produce starting torque. As a result, the synchronous motor is not self-starting.

Induction or Asynchronous AC Motor

The machine which converts the AC electric power into mechanical power by using an electromagnetic induction phenomenon is called an induction motor. The induction motor classified into two types

  • Single phase induction motor
  • Three phase induction motors.

The armature winding in an induction machine functions as both the armature and field winding. The flux in the air gap is created when the stator windings are connected to an AC supply. The flux rotates at a constant rate known as synchronous speed. The stator and rotor windings are both affected by the rotational flux. As it never runs at synchronous speed, an induction motor is also known as an asynchronous motor. Ns = 120f/P, for example. Induction motors are the most extensively used motor in both household and commercial applications.

Incution AC motor con

The stator winding is wound for a certain number of poles in this case. A wrapped rotor or a squirrel cage rotor can be employed. The rotor bars of a squirrel cage rotor are permanently short-circuited with end rings. Since the windings in a wound rotor are permanently short-circuited, no slip rings are necessary. The current passes through the rotor winding and reacts with the rotating flux to produce torque when the rotor circuit is closed. The speed will vary depending on the torque.

Advantages of AC motor 

  • Design is easy & simple
  • The power factor is good
  • Inexpensive
  • An AC source can be directly connected to this motor
  • Good power to weight ratio
  • Maintenance is less

Disadvantages of AC motor 

  • The starting torque of this motor is very less
  • At low speeds, it won’t operate
  • Poor positioning control
  • Limited speed through the frequency supply

Applications

  • It is used in mixer grinders, pumps, and household appliances.
  • Used in industries.
  • they are not appropriate for applications that need very fewer speeds.
  • These motors are a very good choice for applications that need high performance & torque o/p.
  • These motors are used in power tools, clocks, disk drives, fans, blowers, pumps, compressors, conveyors, audio turntables, home appliances, washing machines & industrial areas.

Conclusion:

Hope this article helps you to understand about the working principle,construction,advantages, disadvantages & applications  of an AC motor.

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