Table of Contents
What is Single phase induction motors?
Motor that operate on single phase supply. That motor is called a single phase motors. Such Motors are generally made with ratings ranging from 1/8 HP to 1.5, 2HP; And are useful in many places.
Single phase motors are used in ceiling fans, table fans, refrigerator, fruits mixer, hair dryers, portable drill machine, vacuum cleaner, washing machine, sewing machine, etc.
The quality of a single phase motor is less than the quality of a three phase induction motor. But where only single phase supply is available and low rated motors are required, these motors are suitable.
What is the difference between a 3 phase induction motor and single phase induction motor?
The design of single phase motor and three phase induction motor is similar; The only difference is that the stator winding of a single phase induction motor has a single phase stator winding instead of a three phase.
Why single phase induction motor are not self-start?
If only a single phase winding was fitted to the stator with a single phase supply, the squirrel cage rotor would not receive torque. This means that a single phase induction motor does not start automatically due to a single winding.
Because A.C. Variable magnetic field is generated from single phase supply. Mutual induction causes the E.M.F. Creates; And the eddy current begins to flow.
But as the magnetic field of the stator changes, the current flows through the other 50% of the conductors in the opposite direction to the current flowing through the 50% of the conductors of the rotor.
Since the current flowing through half of the conductors in the same rotor is opposite to each other, simultaneously the rotor receives torque in the same but opposite directions. So the rotor does not rotate in any one particular direction.
This is why single phase motors are not self-start due to a wiring.
If the rotor is rotated by giving torque in any one direction to rotate the motor and supply to the stator, the rotor rotates in the direction of rotation and starts giving mechanical power.
How is a single phase motor self-start?
To automate a single phase motor, a rotating magnetic field must be created in the stator; To make it, the stator of a motor is artificially divided into two phases by two separate windings of different resistances and inductance instead of one winding.
Due to phase division, a rotating magnetic field i.e. phase difference is created and the rotor gets torque and the rotor starts rotating continuously.
What are the starting methods for single phase induction motor self-starting?
- Split phase method
- Shaded pole system
Split phase method
Self start of a single phase induction motor by split phase method is to create a rotating magnetic field by dividing the single phase in the stator of the motor and winding the stator of two phases.
The rotating magnetic field gives the starting torque to the squirrel cage rotor.
To achieve this, an auxiliary or starting winding is installed at 90 degrees along with the main winding in the stator.
The resistance and reactions (inductive reactions or capacitive reactions) of both windings are kept separate.
Therefore, if both windings were to supply a single phase by parallel to each other, different currents would flow through both windings.
The current flowing due to winding resistance is the infusion of voltage and the current flowing due to reactance is the out-of-phase (lagging or lining) of voltage.
This creates a phase difference of 2 degrees in the current flowing through both the windings. Therefore, the fluxes obtained from winding are formed at intervals of θ degrees.
This result is similar to a rotating magnetic field. So the rotating rotor starts with the starting torque of the squirrel cage rotor.
Once the rotor loses its inertia and starts spinning, the rotor continues to rotate in the same direction even if it is opened through a connected winding circuit to generate starting torque. Thus the single phase induction motor is self-started in this manner.
Shaded pole system
Shaded poles are used in the stator of the motor to start a single phase induction motor.
What is a shaded pole?
A shaded pole is a short-circuited ring or strip of thick wire inserted into a notch 1/3 of the pole-shoe of a field pole. This is called a shaded ring.
Field winding is used as stator winding on the pole core. When single winding is supplied to such windings, the rotor rotates with a starting torque to the squirrel cage rotor.
Types of single phase motors
There are 2 main types of single phase motors depending on the design and starting method of single phase motors.
- Split phase induction motor
- Commutator motor,
The following 6 types of split phase induction motors fall.
- Resistance start induction run motor
- Induction start Induction run motor
- Capacitor start induction run motor
- Capacitor start Capacitor run motor
- Permanent capacitor motor
- Shaded pole motor.
The following 2 types of commuter motor fall.
- Universal Motor
- Repulsion motor.
Resistance start Induction run motor
The rotor of this motor has a squirrel cage and the stator is similar to the stator of the 3 phase induction motor. The stator slot has single phase starting and running winding. Running winding has high inductance and low resistance.
The running winding is always mounted at the bottom of the stator slot. Electrical 90 degree starting winding is mounted on the running winding.
Stating windings have higher zest and lower inductance than running windings. This starting winding is only connected to the circuit when the motor starts. Hence this winding is called starting winding. The starting winding is omitted from the circuit when the motor is running.
A centrifugal switch is attached to the series of starting windings. This switch rotor is a mechanical switch that operates on Gifts centrifugal force. Such a switch is mounted inside the motor.
It has a rotating part and a static part as shown in the figure below. The starting winding is connected to the series of this switch. Running or main winding is parallel to supply and starting winding.
The rotating part of the switch is mounted on the shaft of the rotor and the stationary part is mounted on the inside of the end plate.
The fixed part has two contact points, S1 and S2. When the rotor is stationary, the insulating ring of the rotating part is pressed inwards by the spring tension so that the contacts on the fixed part are aligned; And a centrifugal force is formed when the rotor rotates.
That force causes the governor weight on the rotating side to slip, so the insulating ring comes out. So at this time the contactors on the fixed area break and open.
This action also opens the circuit connected to the series of contacts.
The above discussion shows that the centrifugal switch is closed when the motor is off and the switch is open when the motor is rotating.
How does a single phase induction motor start?
When a single phase is supplied to the stator winding by connecting as shown in the figure, the running winding acts as an inductive circuit and the starting winding acts as a resistive circuit.
Therefore, the current flowing through the running winding stays behind about 90 degrees (lagging) of the voltage. At the same time the current flowing through the starting winding is infused close to the voltage.
Therefore, the resulting current of the starting winding and the resulting current flowing through the running winding create a phase difference of 20 to 30 degrees.
Fluxes of both windings are also generated in proportion to that phase difference. This creates a two-phase rotating magnetic field. The squirrel cage rotor receives torque and the rotor starts rotating.
When the speed of the rotor reaches 75 to 80% of its original speed, the centrifugal force of the rotor shaft opens the centrifugal switch.
This opens the circuit of the starting winding and separates it from the starting winding circuit. Then the rotor rotates only because of the magnetic field of the running winding. This is how the split phase motor works.
In the vector diagram shown in the adjacent figure, IRM is the infused current flowing through the main winding. Running or main winding resistance is low. So its vector is less shown. IRS is the infused current in the starting winding. The resistance of the starting winding is high. So its vector is shown more because IXS is due to inductance from starting winding
There is flowing lagging current. Is is the resulting current of starting winding. This effect is the sum of the vectors of infusion and lagging current, starting winding IRS overline a IXS, respectively. (Im) is the resulting current in the main winding. There is an 8th phase difference between the current of starting and main winding. Therefore, a phase difference of 0 ° is created between the currents of both windings and flux is formed at that angular distance. So the rotor gets torque. Rotor
Properties of Resistance Start Induction Run Split Phase Motor:
- Starting torque is low.
- Starting current is high.
- The power factor is low.
- The speed is almost constant.
Where is the resistance start induction run split phase motor used?
This motor is used in places where high starting torque is not required. E.g. Washing machine, ventilating fan, portable batch grinder etc.
Induction Start Induction Run Motor
The design of this motor is similar to resistance start induction run motor, but it does not have a centrifugal switch. This motor is also called a plain split phase motor. Since there is no centrifugal switch, the auxiliary winding is permanently in the circuit along with the main winding.
Capacitor start induction run motor
The design of this motor is as shown in the figure below. Like the split phase motor, this motor has a starting and running winding. The starting winding series consists of a capacitor (60 to 120 microfarads) and a centrifugal switch. The inductance of running winding is high, and it needs to be parallel to the supply. The combination of starting winding, capacitor and centrifugal switch is parallel to the running winding. The structure of the rotor is of squirrel cage type.
Operation of capacitor start induction run motor | How does a capacitor start induction motor work?
When a single phase is supplied to the stator winding, the current flowing through the starting winding is the leading voltage and the current flowing through the running is lagging the voltage.
Therefore, a phase difference is created between the current flowing through both the windings and the rotor gets torque and the rotor starts spinning.
When the rotor reaches 70 to 80 percent speed, the centrifugal force of the rotor shaft opens the centrifugal switch and separates it from the starting winding circuit, but the main winding causes the rotor to rotate continuously.
Properties of Capacitor Start Induction Run Motor
- The starting power factor is good, the running power factor is low.
- The starting current is less than that of a split phase motor.
- Starting torque is good. Running torque is low.
- Price is more expensive than a split phase motor.
How the direction of rotation of a capacitor start induction motor is reversed?
Starting winding or running winding can be done simultaneously to reverse the direction of rotation of the capacitor start induction run motor.
The connection has to be reversed by simply switching the ends of one winding. Or you can change the direction of the motor using a single pole double throw switch as shown in the figure next to it.
Which places capacitor start induction motor are used?
Where good starting torque is required. Use of this motor in such places
Is done. e.g. Compressor, Centrifugal Pump, Refrigerator, Circular Saw. Printing press etc.
Capacitor Start Capacitor Run Motor
This motor is also known as a double capacitor motor. As shown in the figure below, this motor has a rotor squirrel cage and the main winding and auxiliary windings in the stator are electrically connected 90 degree to each other.
One of the two capacitors connected in the circuit is the starting capacitor and the other is the running capacitor. The starting capacitor is connected in series with the centrifugal switch. It usually has a capacity of 60 to 300 microfarads.
The running capacitor is a low capacitance of about 10 microfarads, the main winding is to be connected parallel, and the main winding is paired with a combination of auxiliary winding and running capacitor.
The auxiliary winding is connected to the circuit as long as the motor is running. The auxiliary winding is connected to the circuit as long as the motor is running, not just for the start of the motor. So this winding is not called a starting winding but auxiliary winding.
How does a capacitor start capacitor run motor work?
When the stator winding is supplied, a phase difference is created between the current flowing through the main winding and the current flowing through the auxiliary winding, which gives torque to the rotor.
Therefore, if the rotor rotates and reaches 75-80 percent of its speed, the centrifugal switch opens and separates from the starting capacitor circuit. The rotor then rotates continuously, remaining only in the running capacitor circuit.
Why is this motor called Capacitor Start Capacitor Run Motor?
This type of motor is initially driven by a capacitor and is connected to the capacitor circuit even when running, hence this motor is called a capacitor start capacitor run motor.
Properties of Capacitor Start Capacitor Run Motor
- Starting torque is high.
- Running torque is also good.
- The power factor is good.
- It is better to continue for a long time.
- Efficiency is good.
- Is expensive.
Capacitor Start Uses of Capacitor Run Motor | What is a capacitor start capacitor run motor used for?
Where good starting and running torque is required. This motor is used in such places.
E.g. Refrigerator, air conditioner, lathe machine, compressor, water cooler etc.
Permanent capacitor motor
In this type of motor circuit a low capacity capacitor is permanently connected to the circuit. Hence this motor is called Permanent Capacitor Motor.
This motor has a rotor squirrel cage as shown in the figure. The stator is mounted at 90 degrees to the main winding and auxiliary windings. A series of auxiliary windings have low capacitance (2.5 microfarads) capacitors connected.
This series combination is parallel to the main winding. The main winding is to be connected in parallel to the supply. When the stator is supplied, the current flowing through the main winding is lagged by the voltage. And the current leading through the auxiliary windings. This creates a phase difference and the rotor gets torque and the rotor starts spinning.
Why is a permanent capacitor motor called a fan motor?
This motor is mainly used for ceiling fans in your home / office hence this motor is also called fan motor.
Shaded Pole Motor
As shown in the figure below, The motor rotor is a squirrel cage but the stator has no slots. Dc For the stator of this motor like machine, selector type field poles are installed inside a yoke. One-third of the field pole shoe is hacked. The notch is fitted with a short-circuited winding or a thick strip of copper. This is called shaded coil or shaded ring.
This same shaded ring starts to act like auxiliary winding. The field winding is wrapped around the remaining anchored part of the field pole. The same field winding works as the main winding.
Working Procedure of Shaded Pole Motor | How a shaded pole motor operates?
Field winding on pole core When a single phase supply is given, a changing magnetic field is created around the winding.
This changing magnetic field is cut off from the stable shaded ring. So there is mutual induction in the shaded ring. Therefore, in a shaded ring, an eddy current carries its own magnetic field around the ring.
The magnetic lines around the shaded rings, according to Lenz’s law, oppose the change of the main magnetic line. The magnetic field of the main field is weakened due to resistance to the main flux. Weakening of the main magnetic field reduces the action of induction and also reduces the AD current in the shedding ring.
But the magnetic field created around the shaded ring also resists the reduction of the magnetic field. As the magnetic field of the shaded ring increases again as before, the flux of the field pole moves from the unshared part to the shaded part as the action continues.
The effect of this kind of flux migration is similar to that of a rotating magnetic field. So the squirrel cage rotor in the vicinity of this field starts rotating from the unshaded part of the pole to the shaded part.
This does not change the direction of rotation of the motor. This is clearly seen. So if the direction of rotation of the motor is to be reversed, the entire stator has to be pulled out of the yoke; And has to sit in the opposite direction.
Where is the shaded pole motor used?
The torque of the shaded motor is very low, so no high starting torque is required; This motor is used in such places. E.g. Table fan motor
Universal Motor to AC Also called series motor. This motor A.C. And D.C. This motor is universal as it can run on both such supplies. Called a motor.
As you know, D.C. Armature and field of motor When supplied, the armature starts rotating with armature. In order to change the direction of rotation of the armature, the connection of either the armature or the field has to be reversed.
But if the connection of both armature and field is reversed at the same time, the direction of rotation of the armature does not change. Accordingly, Universal Motor has a D.C. Ajvi A.C. When supplied, A.C. It changes direction along with your price. Therefore, the direction of current flowing through the field and armature of the motor also changes at the same time. Therefore, the armature rotates in the same permanent direction without changing the direction of rotation. C. When connected to the top, the motor rotates slightly faster than the synchronous speed. This speed is not dangerous.
The design of the universal motor
The design of the universal motor is d.c. The series is similar to the motor. This means that field poles are mounted in the yoke for the stator.
By field winding on the field pole it is connected in series of winding armatures. Dc This is an unchanging current. So the D.C. Field Pole laminating is not required in the case of a motor.
But A.C. This constant change produces an eddy current in the core of the field pole; And AD current power loss occurs in the core. Universal Motor A.C. And D.C. Both such supplies can be connected. Hence the design of the Universal Motor in D.C. Unlike a series motor, the pole core is laminated to reduce the current loss in the pole core; And the pole core is made from silicone steel to reduce hysteresis loss.
Properties of Universal Motor
- Rotates at a speed higher than the synchronous speed at no load. But does not rotate at dangerous speeds.
- The speed decreases on load.
- Starting torque is high.
Where is the universal motor used?
This motor is used in domestic use like portable drill machines, mixer, vacuum cleaner, sewing machine, washing machine, hairdresser, etc.
On what principle does a Repulsion Motor operate?
If a short-circuited coil A.C. When placed in a single phase alternating magnetic field, the same magnetic poles form around the coil, and the coil gains torque by diverting into the same pole. The repulsion motor operates on this principle.
Types of repulsion motors
There are three types of repulsion motors
- Plane repulsion motor.
- Repulsion start induction run motor.
- Repulsion induction motor.
Plane repulsion motor
The stator of this motor is similar to the stator of split phase motor
The stator slot has only one concentric winding as the main winding; And the motor’s rotor is, D.C. The armature of the motor is the same. The armature’s front brushes are shortened with a thick wire. These brushes are polar axis and MNA. Are usually placed at 12 to 20 degrees in the centre of Mechanism of Plane Repulsion Motor
When the stator winding is a. C. When a single phase supply is supplied, a changing magnetic field is created in the stator.
Mutual induction due to changing magnetic fields causes emf in the armature. Is created. Since the brushes on the armature are shorted from the outside, AD current flows through the armature conductor. Suppose at that time A.C. The current is going from zero to maximum value in your positive half cycle.
Considering that particular moment, the eddy current of the armature conductor creates a magnetic field around the conductor and a pole like the magnetic field of the stator winding, and due to magnetic repulsion the rotor rotates with torque. The torque received by the rotor and the direction of rotation of the rotor depend entirely on the position of the braces
If the brushes MNA. If kept short, the same emf on both sides of the armature. Is created. So no current flows through the brushes at all. This means that the armature will not receive torque at this position so the rotor will not rotate.
If the brushes are shorted by placing the magnetic pole on the axis, maximum current will flow through the brushes. So the armature will get more current but this torque will get the same amount of torque to the other half of the conductor in the opposite direction to the half of the armature conductor. So even in this position the armature will not rotate.
If the braces are MNA. And a short distance between the polar axis, a greater or lesser current flows on both sides of the armature conductors. Since the current flowing from both the sides is less and more, the armature starts rotating with the torque in the direction of the area where there is more current.
Generally polar axis and MNA. This allows maximum torque when shorted by placing the brushes at 12 to 45 degrees. That is why brushes are always kept in this position. As this angle is increased or decreased, the speed of the armature varies. When the position of the brushes is on the right side, the direction in which the armature rotates, the direction of rotation of the armature changes if the bushes are moved to the left. The speed of the rotor also varies as the position of the brushes changes.
Properties of Plane Repulsion Motor
- Starting torque is good.
- The speed can be increased or decreased by replacing the brushes; Also the direction of rotation can be changed.
- The starting current is low.
- The speed decreases on load.
- Maximum torque can be obtained by shifting the brushes at 45 degrees.
Where is the plane repulsion motor used?
This motor is used for traction work as the torque of the motor is of good quality. E.g. Elevators, cranes, hoists, etc.
Repulsion start induction run motor
This motor is triggered by magnetic repulsion; And rotates like an induction motor. Hence this motor is called Repulsion Start Induction Run Motor.
The stator of this car is similar to the plane repulsion motor. But there are two windings on the rotor, armature winding and squirrel cage winding. Armature winding is called repulsion winding. The repulsion winding is connected to the commuter. A centrifugal switch is mounted in the commutator segment. The commutator segment and the centrifugal switch are open when the motor is stationary. As the motor accelerates, the centrifugal switch shortens the commutator segment and shortens the entire repulsion winding.
How is Repulsion Start Induction Run Motor started?
When the stator winding is supplied, initially the rotor starts rotating with torque to the rotor like a plane repulsion motor according to the principle of repulsion. As the rotor accelerates, the centrifugal force of the rotor shaft closes the centrifugal switch, so the centrifugal switch shortens the repulsion winding. Therefore, the rotor rotates only due to the squirrel cage winding. This means that the motor acts like an induction motor in running.
Properties of Repulsion Start Induction Run Motor
- Starting torque is good.
- Starting current is low.
- Rotates at almost constant speeds on changing loads.
Where is the repulsion start induction run motor used?
This motor is used where good starting torque is required and constant speed is required on changing loads. E.g. Lathe machine, soap machine, water pump etc.
Repulsion induction motor
The stator of this motor is similar to the stator of an induction motor.
The stator slots have a single main winding. Rotor slots have squirrel cage winding at the bottom. It is then armature winding. The armature winding is connected to the commuter.
How is repulsion induction motor started?
When the stator winding is supplied, the rotor frequency is initially high due to the rotor reactivity, so the armature winding only works, not the squirrel cage winding, so the rotor causes the rotor to rotate with torque. As the rotor accelerates, the sleep increases and the rotor frequency decreases. As the rotor frequency decreases, so does the rotor reaction. At that time both windings on the rotor work and the torque of both rotates the rotor helping each other.
Properties of repulsion induction motor
- Good starting and running torque.
- Starting current is low.
- The power factor is good. At full load it is greater than 0.9 lag.
- In running both windings on the rotor result in reduced resistance and less power loss. Is good
- Efficiency is good
Where is the repulsion induction motor used?
Where high starting torque is required. And requires the same speed on changing loads; This motor is used in such places. E.g. Lathe machines, refrigerators, air conditioners, etc.