SINGLE PHASE INDUCTION MOTOR PDF
When you have completed this exercise, you will be able to demonstrate the main operating characteristics of single-phase induction motors. You will start by. Single Phase Induction Motor. ▫. The single-phase induction machine is the most frequently used motor for refrigerators, washing machines, clocks, drills. This paper presents a simple, practical, and effective design, analysis, and selection approach of a capacitor-run single phase induction motor.
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motor, brushless DC motor or BLDC motor and so on. Here, let us discuss in brief about single phase induction motor. Introduction. Single phase induction motor. Single phase induction motors sizes vary from 1/ kw to 1/25 kw are used in toys, hair dryers, vending machines etc. • Universal motor is widely used in. A single phase induction motor is very similar to a 3-phase squirrel cage induction Most of single phase induction motors use squirrel cage rotor as it has a.
A Single Phase Induction Motor consists of a single phase winding which is mounted on the stator of the motor and a cage winding placed on the rotor. A pulsating magnetic field is produced, when the stator winding of the single-phase induction motor shown below is energised by a single phase supply. The word Pulsating means that the field builds up in one direction falls to zero and then builds up in the opposite direction. Under these conditions, the rotor of an induction motor does not rotate. Hence, a single phase induction motor is not self-starting. It requires some special starting means.
They are equal in magnitude but opposite in directions.
The induction motor responds to each of the magnetic fields separately. The net torque in the motor is equal to the sum of the torque due to each of the two magnetic fields. It is known as a Forward Rotating field. The direction in which the single phase motor is started initially is known as the positive direction.
Single-phase Induction Motors
Both the revolving field rotates at the synchronous speed. Thus, the pulsating magnetic field is resolved into two rotating magnetic fields. Both are equal in magnitude and opposite in direction but at the same frequency.
At the standstill condition, the induced voltages are equal and opposite as a result; the two torques are also equal and opposite. Thus, the net torque is zero and, therefore, a single phase induction motor has no starting torque.
Your email address will not be published. Circuit Globe All about Electrical and Electronics. This requires a motor with two windings spaced apart 90 o electrical, fed with two phases of current displaced 90 o in time.
This is called a permanent-split capacitor motor in Figure below. Permanent-split capacitor induction motor. This type of motor suffers increased current magnitude and backward time shift as the motor comes up to speed, with torque pulsations at full speed.
The solution is to keep the capacitor impedance small to minimize losses. The losses are less than for a shaded pole motor. The direction of the motor is easily reversed by switching the capacitor in series with the other winding.
This type of motor can be adapted for use as a servo motor, described elsewhere is this chapter. Single phase induction motor with embedded stator coils. Single phase induction motors may have coils embedded into the stator as shown in Figure above for larger size motors. Though, the smaller sizes use less complex to build concentrated windings with salient poles.
Working Principle of a Single Phase Induction Motor - Circuit Globe
In Figure below a larger capacitor may be used to start a single phase induction motor via the auxiliary winding if it is switched out by a centrifugal switch once the motor is up to speed. Moreover, the auxiliary winding may be many more turns of heavier wire than used in a resistance split-phase motor to mitigate excessive temperature rise. The result is that more starting torque is available for heavy loads like air conditioning compressors. This motor configuration works so well that it is available in multi-horsepower multi-kilowatt sizes.
Capacitor-start induction motor. A variation of the capacitor-start motor Figure below is to start the motor with a relatively large capacitor for high starting torque, but leave a smaller value capacitor in place after starting to improve running characteristics while not drawing excessive current. The additional complexity of the capacitor-run motor is justified for larger size motors.
Capacitor-run motor induction motor.
Working Principle of a Single Phase Induction Motor
Such AC rated electrolytic capacitors have such high losses that they can only be used for intermittent duty 1 second on, 60 seconds off like motor starting.
A capacitor for motor running must not be of electrolytic construction, but a lower loss polymer type.
If an auxiliary winding of much fewer turns of smaller wire is placed at 90 o electrical to the main winding, it can start a single phase induction motor. Figure below With lower inductance and higher resistance, the current will experience less phase shift than the main winding. About 30 o of phase difference may be obtained. Resistance split-phase motor induction motor. This motor has more starting torque than a shaded pole motor next section , but not as much as a two phase motor built from the same parts.
The current density in the auxiliary winding is so high during starting that the consequent rapid temperature rise precludes frequent restarting or slow starting loads.
It is based on the premise that induction motors are inefficient at less than full load. This inefficiency correlates with a low power factor. The less than unity power factor is due to magnetizing current required by the stator. This fixed current is a larger proportion of total motor current as motor load is decreased. At light load, the full magnetizing current is not required. It could be reduced by decreasing the applied voltage, improving the power factor and efficiency. The power factor corrector senses power factor, and decreases motor voltage, thus restoring a higher power factor and decreasing losses.
There is no savings for a fully loaded motor since all the stator magnetizing current is required. The voltage cannot be reduced. But there is potential savings from a less than fully loaded motor. It is safe for the power factor controller to lower the line voltage to VAC. The higher the initial line voltage, the greater the potential savings.
Of course, if the power company delivers closer to VAC, the motor will operate more efficiently without any add-on device. Though, it needs to operate a large number of hours per year. And the more time it idles, as in a lumber saw, punch press, or conveyor, the greater the possibility of paying for the controller in a few years operation.
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