A single phase induction motor consists of a single phase winding on the stator and a cage winding on the rotor. When a 1 phase supply is connected to the stator winding, a pulsating magnetic field is produced. In the pulsating field, the rotor does not rotate due to inertia.
AC single phase motor power calculation:
P(W) = V(V) x I(A) x pf.
The main winding has many turns of large diameter wire wound in the bottom of the stator slots to get high reactance, which is an inductive circuit. The auxiliary winding has few turns of small diameter wire wound to get high resistance, which is a resistive circuit.
Power factor (PF) is the ratio of working power, measured in kilowatts (kW), to apparent power, measured in kilovolt amperes (kVA). Apparent power, also known as demand, is the measure of the amount of power used to run machinery and equipment during a certain period. It is found by multiplying (kVA = V x A).
P = ΔV2 / R
We now have three equations for electrical power, with two derived from the first using the Ohm's law equation. These equations are often used in problems involving the computation of power from known values of electric potential difference (ΔV), current (I), and resistance (R).
Single phase motors work on the same principle as 3 phase motors except they are only run off one phase. A single phase sets up an oscillating magnetic field that goes back and forth rather than a rotating magnetic field (see bottom figure). Because of this a true single phase motor has zero starting torque.
Types of Single Phase Induction Motors
kVA = kw / PF
PF = Power factor.
To start a single-phase induction motor, a capacitor is connected in series with auxiliary winding used to generate a phase difference between the torques which are generated by fluxes equal in magnitude but opposite in direction. The Starting capacitor is short time rated. It is of electrolytic type.
The speed of the single-phase a.c. induction motor can be adjusted either by applying the proper supply voltage amplitude and frequency (called volt-per-hertz control) or by the changing of supply voltage amplitude with constant frequency (slip control).
A single-phase system, circuit, or device has, generates, or uses a single alternating voltage. Single-phase electric power refers to the distribution of alternating current electric power using a system in which all the voltages of the supply vary in unison.
Motor Starting Resistors are used to reduce the voltage at the motor terminals and also decrease the starting current. Motor Starting Resistors are necessary because the self resistance of a motor armature is very low. When the voltage is first applied, excessive current will flow.
Types of Single Phase Induction Motors
What are the Applications of single phase induction motor?
Some single-phase AC electric motors require a "run capacitor" to energize the second-phase winding (auxiliary coil) to create a rotating magnetic field while the motor is running. Start capacitors briefly increase motor starting torque and allow a motor to be cycled on and off rapidly.
A speed reducer is simply a gear train between the motor and the machinery that is used to reduce the speed with which power is transmitted. Speed reducers, also called gear reducers, are mechanical gadgets by and large utilized for two purposes.
Slip refers to the difference between the shaft rotating speed and the magnetic field's synchronous speed, which is measured in frequency or RPM. The percent slip is a method that helps calculate an electric motor's speed performance. A higher load also increases the slip and the amount of torque produced.
There are 5 types of single-phase induction motors on the basis of their starting methods: Resistance start, Capacitor start, Capacitor start capacitor run, Permanent Capacitor, and shaded-pole single-phase induction motor.
From the above topic, we can easily conclude that the single-phase induction motors are not self-starting because the produced stator flux is alternating in nature and at the starting, the two components of this flux cancel each other and hence there is no net torque.
Dated : 29-May-2022
Category : Education