AC Motors - Definition
A.C. motors are induction motors. The air A.C. motor is a motor that transforms alternating current into mechanical energy.
Working Principles, Construction, Classification, and Types
Working Principles
Induction motors operate on the theory that when a closed conductor is placed in a magnetic field, it produces torque, or on the combined action of electromagnetic induction and the motor principle.
Construction
The three-phase induction motor is made up of two parts:
Stator
Rotor
Stator
It is built out of a steel frame that surrounds a hollow, cylindrical cone made up of thin silicon steel laminations to minimize eddy current and hysteresis loss. On the inner periphery of the core, a huge number of similar slots are carved.
The stator conductors are inserted into these slots, which are isolated both from one another and from the slots themselves. A balanced star or delta winding is used to link the conductors. Depending on the speed requirement, the windings are wound for a specific number of poles.
When high speed is required, the winding is wound with fewer poles and vice versa.
Rotor
Any mechanical load can be linked to the rotor, which is positioned on the motor's shaft. There are 2 types of rotors:
Squirrel cage rotor
A squirrel-cage rotor's core is a cylindrical laminated core. It also has parallel slots for rotor conductors. Heavy copper or aluminum bars serve as the rotor's conductors. Each slot receives one bar.
Phase wound rotor
The rotor is made of laminated materials. The cylindrical core features uniform slots in which three-phase star-connected winding is installed. The open ends of the star winding are connected to three insulated slip rings installed on the motor shaft, which are coupled to carbon brushes.
Types
The different types of AC motors are:
Induction motors
Synchronous motors
Single-phase motors
Three-phase motors
Squirrel cage induction motor
Phase wound motor
FAQs on Types of AC Motors
1. How are AC Motors Different from DC Motors?
Nature of the Input Current: For AC motors, the primary input power is alternating current. But for DC motors, direct current provides the input power.
Commutator: AC motors do not have commutators. DC motors are equipped with commutators.
Supply Phase: Single, as well as three-phase supply, is used for AC motors. DC motors operate only with single-phase supply.
Input Terminals: While AC motors have three input terminals (RYB), DC motors have only two input terminals (+, -).
Brushes: There are no carbon brushes in an AC motor. DC motors have carbon brushes for spark-free commutation.
Armature Position: In AC motors, the magnetic field is rotating, and the armature is static. In DC motors, the armature rotates, and the magnetic field is stationary.
Starting: AC motors require external equipment to start. DC motors do not need external help for the start-up operation.
2. What are the advantages and disadvantages of an AC motor?
Advantages
Cost-Effective: Due to its simple design, AC motors are a cost-effective option for various fixed speed applications in the industrial, domestic, and commercial sectors where AC power is readily available. AC motors are frequently found in industrial machinery, air-conditioners, washers, dryers, etc.
Speed Variation: AC motors have a fixed number of built-in winding sets that determine its base speed. The motor speed can be altered by changing the frequency of the AC voltage.
High Power Factor: AC motors have a high power factor. Thus, it draws a lesser current, reducing the energy loss in the distribution system.
Reliability: An AC motor can operate for years without any frequent needs for replacement.
Disadvantages
AC motors cannot operate at speeds lower than 1/3rd of its base speed.
AC motors have a crude and expensive positioning control.
Eddy currents slow down AC motors.
3. What are the applications of AC motors?
The application varies as per the types of AC motors:
Squirrel Cage Motors
These are used in industrial drives such as water pumps, tube wells, lathes, and drills, among other things, to provide power.
Cranes, punch presses, lathes, drills, and other heavy machinery are driven by double cage motors.
Phase Wound Motors
When a high starting torque is necessary, this is the engine to use.
Line shafts, lifts, pumps, and mills, are driven by this type of motor.
Synchronous motors are utilized in a variety of applications such as compressors, paper mills, and the steel rolling industry.
Single-phase motors are commonly used in household electrical appliances such as washing machines, refrigerators, grinders, and blowers, etc.
4. What is the difference between Single Phase and Three Phase motors?
A single-phase induction motor is an alternating current (AC) motor that transforms electrical energy to mechanical energy to perform physical work. A single-phase induction motor requires only one power phase to operate.
This type of ac motor is often utilized in low-power home and industrial applications.
A three-phase motor is an electric machine that uses electromagnetic interactions to transform electrical energy into mechanical energy. The most often used motor for three-phase AC (alternating current) operation is a three-phase induction motor, which does not require any additional starting equipment.
5. Is there any difference between Stator and Motor?
Yes, there is a difference between Stator and Motor on various levels.
Definition
The machine's stator is a stationary component.
The rotor is the motor's rotating component.
Parts
The stator has an outer frame, stator core, and stator winding.
The rotor has Rotor winding and a Rotor core.
Supply
Stator requires three-phase Supply
Rotor requires DC (Direct current) supply
Winding Arrangement
The winding arrangement of the Stator is Complex.
The winding arrangement of the Rotor is Easy.
Insulation
The stator’s insulation is Heavy.
Rotor’s insulation is Less.
Friction Loss
The friction loss for the Stator is High.
The friction loss for Rotor is Low.
Cooling
Cooling the Stator is Easy.
Cooling the Rotor is Difficult.
6. What is the use of Shaft, Bearings, and Enclosure?
The rotor assembly is constructed by pressing it into a steel shaft that stretches outside the motor case, allowing the connection to an external system to broadcast rotational power.
Bearings are installed on the motor's shaft to support the rotor and allow it to rotate. When the shaft of the rotor is revolving, some motors use a fan mounted on the shaft to cool down the motor.
Bearings are used to keep the shaft in position in an ac motor. Bearings will lessen the friction of the shaft that is linked to the casing, allowing the motor to run more efficiently.
A yoke or frame and two end brackets make up the motor's enclosure. The rotor is positioned within the stator through a small air gap that separates it from the stator, which is located within the frame. The rotor and stator do not have a direct physical connection.
The internal parts of the motor are protected from environmental factors and water by the enclosure. Two end brackets and a frame are included in this part.
