Introduction
A synchronous electric
motor is a type of ac motor.it contains multiple phases.The stator
consists of electromagnets and it creates magnetic field.The turns of
electromagnets with respect to stator fields are same.The synchronous motor works
on mutual inductance and the mutual inductance is created between rotor and
stator. Synchronous motor is also used as an alternator or an AC generator.
Types of Synchronous motor
Tere are two major types of Synchronous motor according to
excitation which are as follows:
- Non excited synchronous motor
- Direct Current excited synchronous motor
1. Non excited motor
These types of synchronous motors has a constant magnetic
fields this is because at synchronous speed the rotor with the rotating
magnetic field.The rotor of is made up of steel such as cobalt steel.
Reluctance motor
A type of electric motor that induces non permanent magnetic
poles on the ferromagnetic rotor.the rotor does not have any windings. The
torque is generated through the phenomenon of magnetic reluctance.Reluctance
motor has an ability to deliver high power density at a very low cost.The
stator is similar to a wound field brushed DC motor(which consists of multiple
projecting electromagnetic poles).The rotor consists of soft magnetic
material.The number of rotor poles are less than the stator poles which reduces
the torque ripples,in this situation the torque is not produced.The rotor also
have squirrel cage windings in them to provide torque in them and the motor
starts as an induction motor.
Hysteresis motor
These motors consists of uniform air gap without DC
excitation.It operates both in single and three phase AC supply.The torque in
hysteresis motor is produced due to hysteresis and eddy current induced in a
rotor by the action of the rotating flux of the stator windings. The rotor
consists of hard cobalt steel material,it consists of high magnetization.once
the rotor is magnetized in one direction then it require a huge amount of
reverse magnetic field to reverse the magnetization.
Permanent magnet motors
Permanent magnet motor are similar to brushless DC motor. A
permanent magnet synchronous motors consists of steel rotor to create a
constant magnetic field.The stator consists of windings and are connected to AC
supply to produce a rotating magnetic field. These rotors cannot use induction
windings to start because of the constant magnetic field in rotor.these motors
require a variable power source to start.
DC Excited motors
In this type of motors the rotor is excited with DC power
supply for excitation.The dc power supply is supplied directly through slip
rings.The direct current is supplied from a separate DC source.
Construction
The main components of the synchronous motor are the stator and the rotor.The stator of the synchronous motor and stator of induction motor are same in construction.The stator frames contains wrapper plates.Wrapper plates consists of circumferential ribs and keybars footings are attached on the yoke to carry the weight of synchronous motor.field winding,brushes and slip rings are excited with DC excitation.a salient pole rotor is used when a large numbers of poles are needed in synchronous motors.
Operation
The rotor is excited with dc power supply and the stator
windings are connected to the 3 phase ac supply because the stator windings consists
of 3 phase winding.The 3 phase stator winding produces 3 phase rotating
magnetic flux.The rotor is locked in the rotating magnetic field and rotates
along with it.once the rotor locks in with the rotating magnetic field,the
motor is in a condition of synchronization. A single phase stator winding can also works but in this situation,the
direction is undefined.
Applications
Synchronous motor is used in different fields which are as
follows:
- Synchronous motors are used in generating and sub stations to improve power factor.These motors are used for power factor and are also used in place of synchronous condenser.
- Synchronous motor are also used as fans,blowers,dc generators,line shaft,centrifugal pump,compressor,reciprocating pumps etc.
- Synchronous motor is used to regulate voltages at the end of transmission lines.
- Synchronous motors are used to provide large range of speed with variable frequencies and for constant speed constant load drives in different large scale industries.
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