Why capacitors are used in single-phase motors?
The question is "why a capacitor is used in a single-phase motor". Most of the motors around us are single-phase motors. So
let's start with the basics first. Let's go first
What is a single-phase motor?
Single-phase motor: Simply put, all motors that run on a single-phase supply are called single-phase motors. In the context of Bangladesh, DESCO single-phase supply is 230 volts and frequency is 50 cycles per second.
Detailed discussion of power factor.
How much horsepower does a single-phase motor have?
We have already assumed that single-phase motors tend to be
of smaller quality. These are usually smaller than 1 horsepower but in special
cases, motors range from 1 to 10 horsepower.
Why is a capacitor used in a single-phase motor?
We know that single-phase motors are mainly supplied with AC
power. When an AC supply is provided, an alternating magnetic field is created.
But the magnetic field will not rotate at synchronous speeds
like a three-phase motor. This is because the torque generated by a half
positive cycle is equal to the torque generated by a half negative cycle. As a
result, the combined value of the two torques is zero so the motor cannot
rotate.
This is the main reason why capacitors are used to create a
phase angle difference so that there is a torque difference. This can cause the
motor to rotate.
This is why the fan we use in the house or the motor used to
draw water in the house needs a capacitor.
Working of single-phase induction motor
The working principle of a single-phase induction motor is
based on Faraday's law of electromagnetic induction. The stator winding is
supplied with AC which is a single-phase, the current flowing through the
winding will create a magnetic field called the stator magnetic field. The flux
line of this magnetic field will cross the conductor of the rotor.
Due to the change in the magnetic field of the AC supply
over time the flow is changing, an emf and current will be introduced into the
rotor. The induced current will give rise to another magnetic field called the
rotor magnetic field. A single-phase induction motor differs in operation from
a 3 phase induction motor in the sense that this motor cannot generate a
rotating magnetic field.
Instead of a rotating magnetic field, it creates a magnetic
field that vibrates due to AC oscillation between 0 and 180 degrees. In other
words, the magnetic field does not rotate but reverses 180 degrees. The
interaction of two magnetic fields or magnetic fluxes, one will generate torque
from the stator and the other from the rotor.
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