What is an Induction Motor : Types & Their Working

We know that the main function of a motor is to change the energy from one form to another like electrical to mechanical. The classification of motors can be done based on the type of supply like AC motors & DC motors. Under these AC & DC motors, there are different kinds of motors comes as induction motor, reluctance motor, DC shunt, PMDC, stepper, synchronous, etc. This article discusses an overview of different types of induction motor and their working. This motor is the most commonly used AC motor which is also called asynchronous motor because this motor works at less speed as compared to synchronous speed. Here, synchronous speed is nothing but the rotary magnetic field’s speed within the stator.


What is an Induction Motor?

A motor with only amortisseur windings is called an induction motor. An induction motor is the most modest electrical machine from the construction point of view, in the majority of the cases. The induction motor works on the principle of induction where an electromagnetic field is induced into the rotor when the rotating magnetic field of the stator cuts the stationary rotor. Induction machines are by far the most common type of motor used in industrial, commercial, or residential settings. It is a three-phase AC motor. Its characteristic features are:

Induction Motor
Induction Motor
  • Simple and rugged construction
  • Low cost and minimum maintenance
  • High dependability and sufficiently high proficiency
  • Needs no additional starting motor and necessity not to be synchronized

What are the Basic Parts of an Induction Motor?

An induction motor has basically two parts: Stator and Rotor.

Stator

The stator is made up of various stampings with slots to carry three-phase windings. It is wound for a distinct number of poles. The windings are geometrically divided 120 degrees separated. Two sorts of rotors are used in Induction motors: Squirrel cage rotor and Wound rotor. No DC field current is required to run the machine. Rotor voltage is induced in the rotor windings rather than being physically connected by wires.

Rotor

The rotor is the rotating part of the electromagnetic circuit. The most common type of rotor is the squirrel cage rotor. The rotor comprises a cylindrical laminated core with axially placed parallel slots for carrying the conductors. Each slot carries a copper, aluminum, or alloy bar. The rotor of three-phase induction motors frequently is likewise implied as an anchor. The purpose behind this name is the anchor shape of the rotors used within quite early electrical devices. In electrical equipment, the anchor’s winding would be induced by the magnetic field, although the rotor takes this part in three-phase induction motors.

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An induction motor has the same physical stator as a synchronous machine with an alternate rotor development. Induction motor might be worked as either motors or generator. On the other hand, they are fundamentally used as induction motors.

 Working Principle

The induction motor working principle is, the AC in the rotor of the motor is required to generate torque that is gained through electromagnetic induction which results from the stator winding’s rotary magnetic field.

Types of Induction Motor

Induction motors are classified into two types namely single phase induction motor and three-phase induction motor. As their name suggests, a 1-phase induction motor is connected to a single-phase AC power supply whereas the 3-phase induction motor can be connected to a three-phase AC power supply. Again these types of induction motor are classified into some subcategories. Single-phase is classified into four types whereas 3-phase is classified into two types.


Types of Induction Motor
Types of Induction Motor

Single-phase Induction Motor

The single-phase induction motor is not self-starting. When the motor is connected to a single-phase power supply, the main winding carries an alternating current. It is logical that the least expensive, most reduced upkeep sort engine ought to be utilized most regularly. These are of different types based on their way of starting since these are not self-starting. Those are split phase, shaded pole, and capacitor motors. Again capacitor motors are capacitor start, capacitor run, and permanent capacitor motors. The permanent capacitor motor is shown below.

In these types of motors, the start winding can have a series capacitor and/or a centrifugal switch. When the supply voltage is applied, the current in the main winding lags the supply voltage because of the main winding impedance. And current in the start winding leads/lags the supply voltage depending on the starting mechanism impedance.

The angle between the two windings is sufficient to phase difference to provide a rotating magnitude field to produce a starting torque. At the point when the motor reaches 70% to 80% of synchronous speed, a centrifugal switch on the motor shaft opens and disconnects the starting winding.

Types of Single-Phase Induction Motor

Single-phase induction motor is classified into four types of induction motors like Split Phase, Capacitor Start, Capacitor Start & Capacitor Run, and Shaded Pole Induction Motor.

Split Phase Induction Motor

An alternate name of a split-phase induction motor is a Resistance Start Motor. This kind of motor includes a stator and single cage rotor where the stator includes two windings called starting winding as well as main winding. These two windings are moved 90 degrees within space. The starting winding includes less inductive reactance and high resistance whereas the main winding includes extremely less resistance as well as a high inductive reactance.

This kind of motor is less cost and appropriate for loads that start very easily where the starting frequency can be restricted. This motor is not applicable for drives that need above 1 KW due to the less starting torque. The applications of split-phase inductor motor mainly include a washing machine, floor polishers, AC fans, mixer grinder, blowers, centrifugal pumps, drilling & lathe machine.

Capacitor Start Induction Motor

A capacitor start induction motor is a 1-phase motor that includes a stator as well as a rotor with a single cage. The stator of this motor mainly includes two windings namely main winding as well as an auxiliary winding. An alternate name of an auxiliary winding is starting winding. In motor construction, the arrangement of these two windings can be done 90 degrees separately in space.

  • Capacitor start induction motor is used where frequent starts are needed like higher inertia loads.
  • This kind of motor is used to drive compressors, pumps, machine tools, and conveyors.
  • It is used in AC compressors & the refrigerators

Capacitor Start & Capacitor Run Induction Motor

The capacitor run induction motor working principle is the same as capacitor start induction motor. We know that a 1-phase induction motor is not self-starting as the magnetic field generated is not a rotary type. So for generating a rotary magnetic field, induction motors require phase difference. In a split-phase induction motor, the resistance must be there to create phase difference however in these motors; the capacitor will make a phase difference.

There is a truth that the current flowing throughout the capacitor guides the voltage. In capacitor start & capacitor start capacitor run type motor, there are two windings like the main & the starting.
In starting winding, there is a link within the capacitor thus the current supplying within the capacitor guides the applied voltage through some angle. These two motors include high starting torque so they are mainly used within grinders, conveyors, compressors, air conditioners, etc

Shaded Pole Induction Motor

This is a self-starting 1-phase induction motor where one of the poles of this can be shaded through the copper ring which is also called the shaded ring. The main function of this ring in the motor is like a secondary winding.

This kind of motor turns simply in one specific way & the motor’s reverse movement cannot be possible. In this motor, the power losses are extremely high, the power factor is less & induced starting torque can also be extremely low. The efficiency of this motor is poor due to its small design and low power ratings. The applications of shaded pole induction motor include in small devices such as fans, relays because of its easy starting & low cost.

This motor is used in hairdryers, exhaust fans, table fans, air conditioning, cooling fans, refrigeration device, record players, projectors, tape recorders, machines for photocopying. These motors are also used for initiating electronic clocks as well as 1-phase synchronous timing motors.

Applications

The applications of single phase induction motor are; it is used in low-power applications and widely used in domestic applications as well as industrial. And some of those are mentioned below

  • Pumps
  • Compressors
  • Small fans
  • Mixers
  • Toys
  • High-speed vacuum cleaners
  • Electric shavers
  • Drilling machines

Three-Phase Induction Motor

 These motors are self-starting and use no capacitor, start winding, centrifugal switch, or another starting device. Three-phase AC induction motors are widely used in industrial and commercial applications. These are of two types, squirrel cage, and slip ring motors. Squirrel cage motors are widely used due to their rugged construction and simple design. Slip ring motors require external resistors to have high starting torque.

Induction motors are used in industrial and domestic appliances because these are rugged in construction requiring hardly any maintenance, that they are comparatively cheap, and require supply only to the stator.

Types of 3 Phase Induction Motor

A 3-phase induction motor includes two essential components namely the stator & the rotor. In this motor, the stationary part is the stator whereas the rotating part is the rotor. In this motor, the load is connected to the shaft. Three-phase armature winding can be wound over the stator. Once balanced 3- phase current supplies throughout this winding, then a stable amplitude rotary magnetic field can be formed within the air gap.

This armature winding can be connected toward the three-phase power supply & carries the load current. This kind of motor is classified into two types based on its construction like Squirrel Cage Rotor & Wound Rotor

Squirrel Cage Induction Motor

The squirrel cage induction motor construction is extremely simple. In this motor, the rotor includes a cylindrical core that can be laminated & includes some slots on the external periphery. These slots are not comparable & they are twisted by some angles.

These slots assist to stop magnetic locking among the teeth of the stator & rotor so that smooth operation can be achieved and humming noise can be reduced. These motors include rotors of bars in place of the rotor winding where these bars are fabricated with brass, aluminum otherwise copper.

In this type of motor, the winding of the rotor includes an aluminum bar otherwise uninsulated copper fixed into semi-closed rotor slots. At both ends of this motor, these conductors are short-circuited through similar material’s end ring. As a result, this type of rotor is similar to a squirrel cage, so this is known as a squirrel cage induction motor.

Wound Rotor or Slip Ring Induction Motor

The slip-ring induction motor is also called a wound rotor motor. In this motor, the rotor includes a laminated cylindrical core. Similar to the squirrel cage, there are some slots on the outer periphery. The rotor winding is placed inside the slots.

In the wound rotor, the insulated windings are wound on top of the rotor similarly like on the stator. The winding of this rotor can be distributed uniformly & usually connected in the STAR model. The three terminals of this STAR connection can be taken out throughout the slip ring. So this is the reason to call this motor a slip ring induction motor.

Why 3-Phase Induction Motor is Self Starting?

In a 3-phase motor, there are 3 single-phase lines through a phase difference with 120°. So the rotary magnetic field includes a similar phase difference, so this phase difference will rotate the rotor.

For instance, if we consider a, b & c as three phases once phase ‘a’ gets magnetized, then the rotor will shift towards the phase ‘a’. In the next second phase, ‘b’ will get magnetized, so it will magnetize the rotor & after that phase ‘c’. In this way, the rotor will rotate continuously.

Why 1-Phase Induction Motor is not Self Starting?

Once the supply given to a 1- 1-phase induction motor is single phase then it generates a pulsating magnetic field, not revolving. The current supply throughout a conductor generates a flux which can be determined into two components, where each component will rotate in the reverse direction at a similar speed.

Thus, the net flux will become zero; the flow of current which is induced in the rotor conductors will become zero and torque will be zero. As a result, a single-phase induction motor is not self-starting.
To conquer this trouble & to make this motor self-starting, then this motor can be converted temporarily into a 2-phase motor throughout starting. For this reason, the one-phase motor’s stator is offered through additional winding to the main winding like starting winding. So, these windings are located across the 1-phase supply.

winding can be arranged so that the phase difference among the currents within the two stator winding is extremely large. Thus this motor performs like a two-phase motor. The two current generates a rotating flux which will make the single-phase motor self-starting.

Advantages

The motor construction and the way electric power is supplied all give the induction motor several advantages are shown in the figure below. And let’s see of them in brief.

Advantages of Induction Motor
Advantages of Induction Motor

Low Cost: Induction machines are very cheap when compared to synchronous and DC motors. This is due to the modest design of the induction motor. Therefore, these motors are overwhelmingly preferred for fixed speed applications in industrial applications and for commercial and domestic applications where AC line power can be easily attached.

Low Maintenance Cost: Induction motors are maintenance-free motors unlike dc motors and synchronous motors. The construction of an induction motor is very simple and hence maintenance is also easy, resulting in low maintenance cost.

Ease of Operation: The operation of the induction motor is very simple because there is no electrical connector to the rotor that supply power and current are induced by the movement of the transformer performs on the rotor due to the low resistance of the rotating coils. Induction motors are self-start motors. This can result in reducing the effort needed for maintenance.

Speed Variation: The speed variation of the induction motor is nearly constant. The speed typically varies only by a few percent going from no load to rated load.

High Starting Torque: The starting torque of the induction motor is very high which makes the motor useful for operations where the load is applied before the starting of the motor. 3 phase induction motors will have self-starting torque, unlike synchronous motors. However, single-phase induction motors do not have self-starting torque and are made to rotate using some auxiliaries.

Durability: Another major advantage of an induction motor is that it is durable. This makes it the ideal machine for many uses. This results in the motor running for many years with no cost and maintenance.

All these advantages make induction motor to use in many applications such as industrial, domestic, and in many applications.

Disadvantages

The disadvantages of induction motor include the following.

  • Throughout the light load situation, the power factor is extremely less and it draws a huge current. So, the copper loss can be high which decreases the efficiency throughout the light load situation.
  • The squirrel cage induction motor’s initial torque is not low.
  • This is an invariable speed motor and this motor is not applicable where uneven speed needs
  • This motor speed control is not easy
  • This motor includes a high starting inrush current which will cause a reduction within voltage at the beginning of time.

Applications

The applications of types of induction motor include the following.

  • Lifts
  • Cranes
  • Hoists
  • Large capacity exhaust fans
  • Driving lathe machines
  •  Crushers
  • Oil extracting mills
  • Textile and etc.

Thus, this is all about an overview of types of induction motors. Basically, these are classified into two major types based on the input supply like single-phase and three-phase induction motor. Again, these two types of motors are also sub-divided into different types which are discussed above. Here, Single phase induction motor is not self-starting whereas a three-phase induction motor is a self-starting motor. Here is a question for you, what is the main function of an induction motor?

Induction Motor Based Projects

8 Comments

  1. Nasir shah says:

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    1. Tarun Agarwal says:

      Hi Nasir Shah
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    1. Tarun Agarwal says:

      Hi Nima
      Thank you so much for your response

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    1. Tarun Agarwal says:

      Hi Shabbir
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  5. Pravin Kumar says:

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