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single phase induction motor is not the self starting so, to make it self start we can use capacitor & capacitor also provides high starting torque.
Hi Arif,
To start off, one thing we need to remember that incase of capacitor the current leads the voltage by90 degrees and incase of inductors the voltage leads the current by90 degrees.
Remembering this, we come to the answer. The main restriction with single phase induction motors is that there is only one phase on the stator winding. Hence the magnetic field in a single phase induction motor doesnot rotate. Instead, it pulses, getting first larger and then smaller but always remaining in the same direction. Because there is no rotating stator magnetic field, a single phase induction motor has no starting torque.
Commonly there are three techniques that are used to produce starting torque for single phase induction motors which are1) Split phase windings2) Capacitor type windings3) Shaded stator poles.
The idea behind capacitor start single phase motors is an extension of the split phase winding technique used to produce the starting torque in single phase induction motor. In capacitor start induction motor a capacitor is placed in series with the auxiliary winding of the motor. By propoer selection of capacitor size, the magnetomotive force of the starting current in the auxiliary winding can be adjusted to be equal to the magnetomotive force of the current in the main winding. Now we recall the property of the capacitors the we discussed eariler that the current leads the voltage by90 degrees when capacitor is introduced.
Now with the proper selection of capacitor, the current in the auxiliary windings can be made to lead the current in the main windings by90 degrees.
Moreover we also need to recall, that the capacitor start induction motor concept (single phase) in an extension on the split phase start technique. In split phase technique, the main windings and the auxiliary windings are seperated physically by90 degrees.
So combining the concept of the main and auxiliary windings seperated physically by90 degrees with the concept of90 degrees phase difference introduced by placing a capacitor in series with the auxiliary windings will end up in a creation of a single uniform rotating stator magnetic field and the single phase induction motor will behave just as though it was starting from a three phase power supply.
Hope this helps.
Kind Regards
Hammad Khan
Phase splitting & self starting
single phase induction motor is not the self starting. capacitor produces the torque that makes a90 degrees out of phase between the starting (auxiliary) winding and the running (main) winding. so, to make it self start we can use capacitor & capacitor also provides high starting torque.
For motore starting
Capacitor is used for starting single phase induction motors. It produces the torque that makes a90 degrees out of phase between the starting (auxiliary) winding and the running (main) winding. Hope to give you an idea.
It is used to get high initial torque in initial start of the induction motor in single phase.
To provide the suitable phase angle, to creat a rotating magnetic field.
To provide rotating magnetic field for motor to rotate.
In capacitor-start motor it makes the start winding lead the run winding by 90 degrease so that it acts like a double phase motor. It will then be able to generate a revolving magnetic field which is responsible for giving it a direction.
By providing phase difference between current and voltage and leads current causes to make high starting torque
