Induction Motor

Induction Motor – Types & Advantages

What is an Induction Motor?

A motor with only armortisseur windings is called an induction motor. An induction motor is the most modest electrical machine from constructional point of view, in the majority of the cases. Induction motor works on the principle of induction where electro-magnetic field is induced into the rotor when rotating magnetic field of 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:

• Simple and rugged construction
• Low cost and minimum maintenance
• High dependability and sufficiently high proficiency
• Needs no additional starting motor and necessity not 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.

Induction Motor

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 of 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.

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.

Two Types of Induction Motors

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 of not self starting. Those are split phase, shaded pole and capacitor motors. Again capacitor motors are capacitor start, capacitor run and permanent capacitor motors. 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, 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 angel between the two windings is sufficient phase difference to provide a rotating magnitude field to produce a starting torque. 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.

Applications of Single Phase Induction Motor

These are 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 other 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 industry 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.

Applications of Three Phase Induction Motor

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

Advantages of Induction Motor

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

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 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 induction motor is very simple and hence maintenance is also easy, resulting in low maintenance cost.

Ease of operation:  Operation of induction motor is very simple because there is no electrical connector to the rotor that supply power and current is 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 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 staring torque of induction motor is very high which makes motor useful for operations where 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 does not have self starting torque and are made to rotate using some auxiliaries.

Durability: Another major advantage an induction motor is that it is durability. This makes it the ideal machine for many uses. This results the motor to run 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.

Induction Motor Based Projects

• Induction Motor Protection System

• Electronic Soft Start for 3 Phase Induction Motor

• Smooth Start of a Single Phase Induction Motor