Single Phase Motor: Questions Answered

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In summary, a single phase induction motor is not self-starting due to the presence of two opposite magnetic fields caused by the main winding. To start the motor, an external force is needed to create a rotating vector field by combining the main and start windings. Once the motor is running, the induced current in the armature is enough to maintain rotation. The phase difference between the armature and main winding creates a directional torque that allows the motor to continue running. The start capacitor provides a phase shifted current to excite the start winding and aid in starting the motor.
  • #1
NT DANG KHOA
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Dear expert, dear all.
As my knowledge, the single phase motor is not a seft-starting motor. i suppose that there is only main winding in single phase motor.
as you know, the rotor can not start because of the 2 opposites force cause by 2 oppositely rotating magnetic fields.
the question is that :
1. Why we give the 1 phase motor an external force in either direction , the motor will start to run ? ( i think the motor only run for short time until this force run out , because it always exist 2 opposites force when the main winding of stator have power supply. like we turn the wheel by hand )
2. with a normal single phase motor ( starting winding with a capacitor and main winding ) what is the cause can make the speed of the motor increase because the capacitor and the starting winding only give it the constant force in the starting period, and why we cut out the starting winding , the motor continue increase speed to the rated speed while there is only 1 main winding which have cause the 2 same opposites force ?
Forgive me if my eng is not good and it is a stupid question,
thank in advance.
 
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  • #2
Welcome to PF.

A single phase induction motor has a start winding that is wound at 90° phase to main winding.
The start capacitor provides a phase shifted current that excites the start winding.
The sum of the magnetic field from main and start winding is a true rotating vector field.

Once the motor is running the current induced in the armature is sufficient to maintain rotation.
 
  • #3
Baluncore said:
Welcome to PF.

A single phase induction motor has a start winding that is wound at 90° phase to main winding.
The start capacitor provides a phase shifted current that excites the start winding.
The sum of the magnetic field from main and start winding is a true rotating vector field.

Once the motor is running the current induced in the armature is sufficient to maintain rotation.
SORRY BUT COULD YOU EXPLAIN MORE DETAIL ABOUT THIS SENTENCE "Once the motor is running the current induced in the armature is sufficient to maintain rotation"
 
  • #4
The current induced in the rotating armature has a phase delay that makes it not parallel with the field windings.
Because there is a phase difference between armature and main winding there is a directional torque.
http://en.wikipedia.org/wiki/AC_motor#Slip
 

FAQ: Single Phase Motor: Questions Answered

What is a single phase motor?

A single phase motor is an electric motor that operates on a single phase power supply. This means that the power source provides alternating current (AC) in only one direction, rather than the three phases typically found in industrial power systems.

How does a single phase motor work?

A single phase motor works by using a single phase power supply to create a rotating magnetic field. This field interacts with the motor's stator and rotor, causing the rotor to rotate and create mechanical energy.

What are the advantages of a single phase motor?

One advantage of a single phase motor is its simplicity and lower cost compared to three phase motors. They are also easier to install and maintain, making them a popular choice for smaller applications.

What are the disadvantages of a single phase motor?

A major disadvantage of a single phase motor is its lower power output compared to three phase motors. They also tend to be less efficient and have a lower starting torque, which can limit their use in certain applications.

Can a single phase motor be converted to a three phase motor?

Yes, it is possible to convert a single phase motor to a three phase motor. This can be done by using a phase converter or rewinding the motor's stator. However, this process can be complex and may not always be cost-effective.

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