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Difference between Stator and Rotor in Rotating Electric Machines
A rotating electric machine is the one which has moving parts. Every rotating electrical machine such as motor and generator consists of two major parts namely stator and rotor. As their name implies, the stator is that part of the machine which is stationary or non-movable, whereas the rotor is the part which can move or rotate freely.
This article is meant for explaining the differences between stator and rotor of an electrical machine. But before going into the comparison of stator and rotor we shall discuss what the stator and rotor are.
What is Stator of Electrical Machine?
As its name implies, the stator of a rotating electrical machine is the part which does not move or remains stationary. Therefore, the stator is a static part of the machine. The primary function of the stator of an electric machine is to provide housing to the stator winding to produce magnetic field in the machine.
A typical stator consists of three major parts namely stator frame (or yoke), stator core and stator winding. The stator frame protects the internal structure of the machine from the mechanical damages. The stator core has slots on its inner periphery for placement of the stator winding. The stator winding is basically an inductive coil of copper or aluminium conductors which carries electric current to produce the working magnetic field in the machine. The core of stator of an electric machine is usually made of laminations of high-grade silicon steel.
What is Rotor of Electric Machine?
The rotor is the rotating or moving part of an electric machine. A typical rotor of an electric machine consists of three major parts namely rotor core, rotor shaft and rotor winding. The rotor core is made from steel laminations stacked together. The rotor core has slots cut on its outer periphery to carry the rotor winding. The rotor winding is made of copper conductors either in the form of winding or in the form squirrel cage. The rotor winding may be excited either by an external source of DC power or by the electromagnetic induction due to stator’s magnetic field.
If the given electric machine is a motor, then a mechanical load is connected to shaft of the rotor, and if the machine is a generator, then the shaft is rotated by a prime mover like turbine, diesel engine, etc.
Difference between Stator and Rotor
The following table highlights all the significant differences between stator and rotor by considering different parameters −
| Basis of Difference | Stator | Rotor |
|---|---|---|
| Definition | The stationary part of any electric machine (motor or generator) is known as stator. | The moving or rotating of an electric machine is known as rotor. |
| Parts | The stator of an electric machine consists of three major parts namely stator frame, stator core and stator winding. | The rotor of an electrical machine consists of three main parts namely rotor core, rotor winding and rotor shaft. |
| Slots location | In case of stator, the slots are cut on the inner periphery of the stator core. | In case of rotor, the slots are cut on the outer periphery of the rotor core. |
| Types | There is no further classification of stator, because every machine has almost same stator construction. | There are two types of rotor construction namely squirrel cage rotor and wound rotor. |
| Function in motor | The main function of stator in an electric motor is to produce the working magnetic field (known as RMF or rotating magnetic field). | The function of the rotor in an electric motor is to drive the mechanical load, which is attached to the rotor shaft. |
| Function in generator | In case of generator, the stator acts as the armature and hence generates the emf (or electricity). | The rotor of a generator acts as the source of revolving magnetic field and it is rotated by some external mean like turbine, diesel engine, etc. |
| Arrangement of winding | The arrangement of stator winding is comparatively complicated because it is placed in slots cut on the inner periphery of the stator core. | The arrangement of rotor winding is simple. |
| Weight | The stator of an electrical machine is relatively heavy. | The weight of the rotor of an electric machine is less as compared to the stator. |
| Friction loss | No friction loss occurs in the stator of the machine as it is a static part. | The friction loss occurs in the rotor because it is moving part. |
| Requirement of insulation | Stator requires high insulation between windings and core because the stator windings carry relatively high currents. | Rotor requires less insulation because the rotor winding current is less. |
| Cooling | The cooling of stator is easy and simple because the stator is the outer part of the electrical machines. | The cooling of the rotor is difficult because it is the internal part of the machine. |
Conclusion
The most significant difference that you should note here is that the Stator is a stationary part of the machine, while the Rotor is a movable part of the machine. Both Stators and Rotors play crucial parts in every rotating electrical machine.
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