in this article we share knowledge about the working of single phase induction motor. We will discuss about the basic working of single phase induction motor.
Ferade law
Working of Single phase induction motor
Such motors, which are designed to operate from a single
phase supply, are manufactured in large number of types to perform a wide
variety of useful services in home offices factories workshops and business
establishments etc. Small motors, particularly in the fractional kilo watt
sizes are better known than any other.
The working of Single phase induction motor is totaly depend on ferade law of electromagnetic
induction.
Ferade law
“ The rate of change of flux is directly proportional to
induce EMF in the coil or conductor”.
Types of single phase induction motor
For better understanding the working of single phase induction motor it required to know about the types of single phase induction motor.
1. Induction motor (split phase, capacitor and shaded pole
etc.)
2. Repulsion motors (some times called inductive-series
motors)
3. AC series motor
4. UN-excited Synchronous motors
Construction ally, single phase induction motor is, more or
less, similar to a poly phone induction, except that
1.
Its stator is provide with a single phase
winding and
2.
A
centrifugal switch is used in some types of motors, in order to cut out a
winding, used only for starting purposes. It has distributed stator winding and
a squirrel-cage rotor. When fed from a single-phase supply, its stator winding
produces a flux (or field) which is only alternating. one which alternates
along one space axis only. It is not a synchronously revolving (or rotating)
flux, as in the case of a two –or a three-phase stator winding, fed from a 2-or
3-phase supply. Now alternating or pulsating flux acting on a stationary
squirrel-cage rotor cannot produce rotation (only a revolving flux can). That
is why a single phase motor is not self starting.
However, if the rotor of such a machine is
given a initial start by hand (or small motor) or otherwise, in either
direction , then immediately a torque arises and the motor accelerates to its
final speed ( unless the applied torque is too high ).
This particular behavior of the motor has
been explained in two ways :
1. Applying double-field revolving theory
2. Applying of cross-field theory
Double field revolving theory
This theory makes use of the idea that an alternating
uni-axial quantity can be represented by two oppositely-rotating vectors of
half magnitude.Accordingly,an alternating sinusoidal flux can be represented by
two revolving flux. Each equal to half the value of the alternating flux and
each rotating synchronously (Ns=120f/p) in opposite direction.
Single phase induction motor self starting
For know more about working of single phase induction motor. We give explanation about the starting of single phase induction motor.
AS we know that a single phase induction motor is not self starting .to improve this drawback and make the motor self starting, it is temporarily converted into a two phase motor winding during starting period. For this purpose ,the stator of a single –phase motor is provided with an extra winding ,in addition to main winding or running winding. The two winding are spaced 90 degree electrically apart and are connected in parallel across the single-phase supply as shown in diagram
AS we know that a single phase induction motor is not self starting .to improve this drawback and make the motor self starting, it is temporarily converted into a two phase motor winding during starting period. For this purpose ,the stator of a single –phase motor is provided with an extra winding ,in addition to main winding or running winding. The two winding are spaced 90 degree electrically apart and are connected in parallel across the single-phase supply as shown in diagram
It is so arranged that the phase difference between the
current in the two stator winding is very large (ideal value being 90 degree).
Hence,the motor behaves like a two phase motor .These two current produced a
revolving flux and hence make the motor self starting.
It is the working of single phase induction motor if will find any incorrect in above article pleaz comment below in comment box.