AC machines are electric motors. The working of AC machines is based on rotating magnetic field. DC motors which dosent has brush are actually an AC machine. It is operated by Alternate current. It converts electrical energy in to mechanical energy or mechanical energy in to electrical energy. When it converts mechanical to electrical then it is called generators. And if it converts electrical to mechanical then it is known as motors. AC machines are also known as induction motors.
We have two types of electric motors:
1. AC machines
2. DC machines
AC machines are further classified in two types:
1. Asynchronous (it runs slower than supply frequency, it also works as prime movers)
2. Synchronous (it runs similar to the supply frequency, it also works as stepper motor)
AC machines are classified in another way on the basis of power supply:
1. Single phase AC machine (normally applied in low power need like mixer grinder, ceiling fans)
2. Three phase AC machine: in this three different set of windings are put in stator. (Normally applied in high power need like air conditioning, hydraulic pumps, irrigation pumps etc.)
The operation of asynchronous motor is depends on following facts:
1. Motor action: when an iron rod halt temporarily in a magnetic field.
2. Transformer action: stator is connected with power supply; current is generated in rotor windings.
3. Rotating field: rotating magnetic field can be formed by stator poles.
If we talk about the speed of AC motor then it is 3000 rpm for 50 Hz supply.
Ac machines also have some losses such as:
1. Hysteresis loss (it is proportional to the area of hysteresis loop)
2. Eddy current loss (when the material that conducts heat or electricity, make visible to a changing magnetic field)
Combinely, above losses are known as core loss.
Basic parts of AC motor: stator (produce rotating magnetic field and have coils, it is an outer part, it is connected with AC power supply) and rotor (produces torque, it is an inner part, squirrel cage is commonly used rotor, it is constructed with great density copper rods)
AC motors are used in manyfields such as commercial, industrial, residential etc.
Applications of AC machines:
1. In high power filed.2. In machine tools3. In electric and hybrid motors4. In permanent magnet motors5. In house hold appliances (hair dryer, vacuum cleaner, blenders etc.)6. In light industries7. In fixed application such as clocks and timer.
Advantages of AC machines:
1. Voltage can be stepped up or down in AC machines
2. Energy loss is less
3. Simple slip ring is used
4. High voltage
5. Overall good efficiency
6. Less parts to fail
As every coin has two phases in same way AC machines have some disadvantages as well, mentioned below:
1. Supplied EMF opposed by back EMF
2. Insulation and shielding are needed by wires
3. Frequency should continue with 50 Hz for operation
AC machines play very essential part in our day to day life like from water pumping to modern robot.AC motors are simple, tough in construction, and relatively economic in construction because it has no external connection and it is a self contained object.
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