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applications of different types of single phase induction motors

warum bleiben manche frauen single The are made self starting by providing an additional flux by some additional means. Now depending upon these additional means the single phase induction motors are classified as:

  1. Split phase induction motor.
  2. Capacitor start meine stadt fürth sie sucht ihn motor.
  3. Capacitor start run (two value capacitor method).
  4. Permanent split capacitor (PSC) motor.
  5. Shaded pole induction motor.

Split Phase Induction Motor

In addition to warum frauen single bleiben the main schindelhauer siegfried singlespeed fahrrad winding or running winding, the stator of single phase induction motor carries another winding called auxiliary warum frauen single bleiben winding or starting winding. A centrifugal switch is connected in series with auxiliary winding. The purpose of this switch is to disconnect the auxiliary winding from the main circuit when the motor attains a speed up to 75 to 80% of the synchronous speed. We know that the running winding is inductive in nature. Our aim is to create the phase difference between the two winding and this is possible if the starting winding carries high. Let schindelhauer siegfried singlespeed fahrrad us say

Irun is the flowing through the main or running winding, Istart is the current flowing in starting winding, and VT is the supply voltage. split phase induction motor

We know that for highly resistive winding the current is almost in phase with the and for highly inductive winding the current lag behind the voltage by large angle. The starting winding is highly resistive so, the current flowing in the starting winding lags behind the applied voltage by very small angle and the running winding is highly inductive in nature so, the current flowing in running winding lags behind applied voltage by large angle. The resultant of these two current is IT. The resultant of these two current produce rotating which rotates in one direction. In split phase induction motor the starting and main current get splitted from each other by some angle so this motor got its name as split phase induction motor.

Applications of Split Phase Induction Motor

Split phase induction motors have low starting current and moderate starting torque. So these motors are used in fans, blowers, centrifugal pumps, washing machine, grinder, lathes, air conditioning fans, etc. These motors are available in the size ranging from 1 / 20 to 1 / 2 KW.

Capacitor Start IM and Capacitor Start Capacitor Run IM

capacitor start run induction motor The working principle and construction of Capacitor start inductor motors and capacitor start capacitor run induction motors are almost the same. We already know that single phase induction motor is not self starting because the magnetic field produced is not rotating type. In order to produce rotating magnetic field there must be some phase difference. In case of split phase induction motor we use resistance for creating phase difference but here we use capacitor for this purpose. We are familiar with this fact that the flowing through the capacitor leads the voltage. So, in capacitor start inductor motor and capacitor start capacitor run induction motor we are using two winding, the main winding and the starting winding. With starting winding we connect a capacitor so the current flowing in the capacitor i.e Ist leads the applied voltage by some angle, φst.

The running winding is inductive in nature so, the current flowing in running winding lags behind applied voltage by an angle, φm. Now there occur large phase angle differences between these two currents which produce an resultant current, I and this will produce a rotating magnetic field. Since the torque produced by these motors depends upon the phase angle difference, which is almost 90o. So, these motors produce very high starting torque. In case of capacitor start induction motor, the centrifugal switch is provided so as to disconnect the starting winding when the motor attains a speed up to 75 to 80% of the synchronous speed but in case of capacitor start capacitors run induction motor there is no centrifugal switch so, the >capacitor remains in the circuit and helps to improve the and the running conditions of single phase induction motor.

Application of Capacitor Start IM and Capacitor Start Capacitor Run IM

These motors have high starting torque hence they are used in conveyors, grinder, air conditioners, compressor, etc. They are available up to 6 KW.

Permanent Split Capacitor (PSC) Motor

It has a cage rotor and stator. Stator has two windings – main and auxiliary winding. It has only one capacitor in series with starting winding. It has no starting switch. Advantages and Applications No centrifugal switch is needed. It has higher efficiency and pull out torque. It finds applications balvenie triple cask 12-rig single malt in fans and blowers in heaters and air conditioners. It is also used to drive office machinery.

Shaded Pole Single Phase Induction Motors

shaded pole single phase induction motor The stator of the shaded pole single phase induction motor has salient or projected poles. These poles are shaded by copper band or ring which is inductive in nature. The poles are divided into two unequal halves. The smaller portion carries the copper band and is called as shaded portion of the pole.

ACTION: When a single phase supply is given to the stator of shaded pole induction motor an alternating flux is produced. This change of flux induces emf in the shaded coil. Since this shaded portion is short circuited, the current is produced in it in such a direction to oppose the main. The flux in shaded pole lags behind the flux in the unshaded pole. The phase difference between these two fluxes produces resultant rotating flux. We know that the stator winding current is alternating in nature and so is the flux produced by the stator current. In order to clearly understand the working of shaded pole induction motor consider three regions-

  1. When the flux changes its value from zero to nearly maximum positive value.
  2. When the flux remains almost constant at its maximum value.
  3. When the flux decreases from maximum positive value to zero.
REGION 1: When the flux changes its value from zero to nearly maximum positive value – In this region the rate of rise of flux and hence current is very high. According to whenever there is change in flux emf gets induced. Since the copper band is short circuit the current starts flowing in the copper band due to this induced emf. This current in copper band produces its own flux. Now according to the direction of this current in copper band is such that it opposes its own cause i.e rise in current. So the shaded ring flux opposes the main flux, which leads to the crowding of flux in non shaded part of stator and the flux weaken in shaded part. This non uniform distribution of flux causes magnetic axis to shift in the middle of the non shaded part.

REGION 2: When the flux remains almost constant at its maximum value- In this region the rate of rise of current and hence flux remains almost constant. Hence there is very little induced emf in the shaded portion. The flux produced by this induced emf has no effect on the main flux and hence distribution of flux remains uniform and the magnetic axis lies at the center of the pole.

REGION 3: When the flux decreases from maximum positive value to zero - In this region the rate of decrease in the flux and hence current is very high. According to whenever there is change in flux emf gets induced. Since the copper band is short circuit the current starts flowing in the copper band due to this induced emf. This current in copper band produces its own flux. Now according to the direction of the current in copper band is such that it opposes its own cause i.e decrease in current. So the shaded ring flux aids the main flux, which leads to the crowding of flux in shaded part of stator and the flux weaken in non shaded part. This non uniform distribution of flux causes magnetic axis to shift in the middle of the shaded part of the pole. This shifting of magnetic axis continues for negative cycle also and leads to the production of rotating magnetic field. The direction of this field is from non shaded part of the pole to the shaded part of the pole.

Advantages and Disadvantages of Shaded Pole Motor

The advantages of shaded pole induction motor are
  1. Very economical and reliable.
  2. Construction is simple and robust because there is no centrifugal switch.
The disadvantages of shaded pole induction motor are
  1. Low power factor.
  2. The starting torque is very poor.
  3. The efficiency is very low as, the copper losses are high due to presence of copper band.
  4. The speed reversal is also difficult and expensive as it requires another set of copper rings.

Applications of Shaded Pole Motor

Applications of Shaded pole motors induction motor are- Due to their low starting torques and reasonable cost these motors are mostly employed in small instruments, hair dryers, toys, record players, small fans, electric clocks etc. These motors are usually available in a range of 1/300 to 1/20 KW.

Where three-phase power is unavailable or impractical, it’s single-phase motors to the rescue. Though they lack the higher efficiencies of their three-phase siblings, single-phase motors — correctly sized and rated — can last a lifetime with little maintenance.

Occasionally a manufacturing defect can result in early motor failure. However, most failures come from inappropriate application. Pay careful attention to application requirements before choosing a motor for replacement of a failed one or for a new design application. Not choosing the correct motor type and horsepower can cause repeated motor failure and equipment downtime. Obviously, you don’t want to specify a motor too small for the application, thus resulting in electrical stresses that cause premature motor failure. But neither should you specify a motor too powerful — either because of its power or its inherent design characteristics. It can also have serious effects. For example, a motor with high locked-rotor and breakdown warum bleiben manche frauen single torques can damage the equipment it drives. Also, running a motor at less than full rated load is inefficient, costing you money for power wasted.

The key: First, size the motor to the application but, just as importantly, understand the characteristics of the major types of single-phase motors — characteristics that go right to the heart of matching a motor to an application.

In general, an ac polyphase squirrelcage motor connected to a polyphase line will develop starting torque. A squirrelcage motor connected to a single-phase line develops no starting torque, but having been started by some external means, it runs approximately like a polyphase motor. The many types of single-phase motors are distinguished mostly by the means by which they are started.

Split-phase

The split-phase motor, also called an induction-start/induction-run motor, is probably the simplest single-phase motor made for industrial use, though somewhat limited. It has two windings: a start and a main winding, . The start winding is made with smaller gage wire and fewer turns relative to the main winding to create more resistance, thus putting the start winding’s field at a different electrical angle than that of the main winding, and causing the motor to rotate. The main winding, of heavier wire, keeps the motor running the rest of the time.

A split-phase motor uses a switching mechanism that disconnects the start winding from the main winding when the motor comes up to about 75% of rated speed. In most cases, it is a centrifugal switch on the motor shaft.

The split-phase motor’s simple design makes it typically less expensive than other single-phase motor types for industrial use. However, it also limits performance. Starting torque is low, typically 100 to 175% of rated load. Also, the motor develops high starting current, approximately 700 to 1,000% of rated. Consequently, prolonged starting times cause the start winding to overheat and fail; so don’t use this motor if you need high starting torque.

Other split-phase motor characteristics: Maximum running torque ranges from 250 to 350% of normal. Plus, thermal protection is difficult because the high locked-rotor current relative to running current makes it tricky to find a protector with trip time fast enough to prevent start-winding burnout. And, these motors usually are designed for single voltage, limiting application flexibility.

Good applications for split-phase motors include small grinders, small fans and blowers, and other low startingtorque applications with power needs from 1/20 to 1/3 hp. Avoid applications requiring high cycle rates or high torque.

Capacitor-start/induction-run

Here is a true wide-application, industrial-duty motor. Think of it as a splitphase motor, but with a beefed-up start winding that includes a capacitor in the circuit to provide a start “boost,”. Like the split-phase motor, the capacitor- start motor also has a starting mechanism, either a mechanical or solid-state electronic switch. This disconnects not only the start winding, but also the capacitor when the motor reaches about 75% of rated speed.

Capacitor-start/induction-run motors have several advantages over split-phase motors. The capacitor is in series with the start circuit, so it creates more starting torque, typically 200 to 400% of rated load. And starting current, usually 450 to 575% of rated current, is much lower than that of the split-phase due to the larger wire in the start circuit. This allows higher cycle rates and reliable thermal protection.

The cap-start/induction-run motor is more expensive than a comparable splitphase motor because of the additional cost of the start capacitor. But the application range is much wider because of higher starting torque and lower starting current. Use the motors on a wide range of belt-drive applications like small conveyors, large blowers and pumps, and many direct-drive or geared applications. These are the workhorses of general-purpose industrial motors.

Permanent split capacitor

A permanent split capacitor (PSC) motor, , has neither a starting switch nor a capacitor strictly for starting. Instead, it has a run-type capacitor permanently connected in series with the start winding. This makes the start winding an auxiliary winding once the motor reaches running speed. Because the run capacitor must be designed for continuous use, it cannot provide the starting boost of a starting capacitor. Typical starting torques of PSC motors are low, from 30 to 150% of rated load, so these motors are not for hard-to-start applications. However, unlike split-phase motors, PSC motors have low starting current, usually less than 200% of rated load current, making them excellent for applications with high cycle rates. Breakdown torque varies depending on design type and application, though it is typically somewhat lower than with a capstart motor.

PSC motors have several advantages. They need no starting mechanism and so can be reversed easily. Designs can be easily altered for use with speed controllers. They can also be designed for optimum efficiency and high power factor at rated load. And they’re considered the most reliable of single-phase motors, mostly because no starting switch is needed.

Permanent split capacitor motors have a wide variety of applications depending on the design. These include fans, blowers with low starting-torque needs, and intermittent cycling uses such as adjusting mechanisms, gate operators, and garage-door openers, many of which also need instant reversing.

Capacitor-start/capacitor run This type, , combines the best of the capacitor-start/induction-run motor and the permanent split capacitor motor. It has a start-type capacitor in series with the auxiliary winding like the capacitor-start motor for high starting torque. And, like a PSC motor, it also has a run-type capacitor that is in series with the auxiliary winding after the start capacitor is switched out of the circuit. This allows high breakdown or overload torque.

Another advantage of the capacitorstart/ capacitor-run type motor: It can be designed for lower full-load current and higher efficiency. Among other things, this means it operates at lower temperature than other single-phase motor types of comparable horsepower.

The only disadvantage to a capstart/ cap-run motor is its higher price — mostly the result of more capacitors, plus a starting switch. But it’s a powerhouse, able to handle applications too demanding for any other kind of single-phase motor. These include woodworking machinery, air compressors, high-pressure water pumps, vacuum pumps, and other hightorque applications requiring 1 to 10 hp.

Shaded-pole

Unlike all the previous types of singlephase motors discussed, shaded-pole motors have only one main winding and no start winding,. Starting is by means of a design that rings a continuous copper loop around a small portion of each motor pole. This “shades” that portion of the pole, causing the magnetic field in the ringed area to lag the field in the unringed portion. The reaction of the two fields gets the shaft rotating.

Because the shaded-pole motor lacks a start winding, starting switch, or capacitor, it is electrically simple and inexpensive. Plus, speed can be controlled merely by varying voltage, or through a multitap winding. Mechanically, shaded-pole motor construction allows high-volume production. In fact, these are usually considered “disposable” motors — they are much cheaper to replace than to repair.

The shaded-pole motor has many positive features, but it also has several disadvantages. Its low starting torque is typically 25 to 75% of full-load torque. It is a high slip motor with running speed 7 to 10% below synchronous speed, Also, it is very inefficient, usually below 20%.

Low initial cost suits shaded-pole motors to low-horsepower or light-duty applications. Perhaps their largest use is in multispeed fans for household use. But low torque, low efficiency, and less sturdy mechanical features make shaded-pole motors impractical for most industrial or commercial uses where higher cycle rates or continuous duty are the norm.

The preceding information establishes guidelines to determine the proper motor type for your application. However, there are special cases and applications in which it is acceptable to vary from these guidelines. Make it a point to check with your motor manufacturer for technical support in these areas.

Capacitors

Start capacitor. The electrolytic start capacitor helps the motor achieve the most beneficial phase angles between start and main windings for the most locked-rotor torque per locked-rotor ampere. It is disconnected from the start circuit when the motor reaches about 75% of full-load speed.

The start capacitor is designed for short-time duty. Extended application of voltage to the capacitor will cause premature failure, if not immediate destruction.

Typical ratings for motor start capacitors range from 100 to 1,000-microfarad (μF) capacitance and 115 to 125 Vac. However, special applications require 165 to 250-Vac capacitors, which are physically larger than capacitors of lower voltage rating for the same capacitance. Capacitance is a measure of how much charge a capacitor can store relative to the voltage applied.

Run capacitor. These are constructed similarly to start capacitors, except for the electrolyte. They are designed to serve continuously in the run circuit of a capacitor- start/capacitor-run motor. They withstand higher voltages, in the range of 250 to 370 Vac. They also have lower capacitance, usually less than 65 μF.

Kevin Heinecke is an electrical design engineer in the AC Motor Group,, Grafton, Wis. He has been with Leeson 8 years and holds an electrical engineering degree from, along with an associate degree in electromechanical technology from.

Related Articles

Single phase induction motors are used in a wide range of applications where only single phase supply is available.

These are manufactured in fractional kilowatt range to meet the requirements of various applications such as ceiling fans, food mixers, refrigerators, vacuum cleaners, portable drills, hair driers, etc.

Let us discuss various types of single phase induction motors in brief.

Table of Contents

Introduction to Single Phase Induction Motors

As the name suggests, these motors operate on single phase AC supply. Single phase induction motors are extensively used in low power applications such as domestic appliances as mentioned above.

These are small in size and less expensive to manufacture. These motors are also called as fractional KW motors, because most of these motors are constructed in fractional kilo-watt capacity.

Single phase induction motors consist of two main parts; stator and rotor. The construction of these motors is more or less similar to a three-phase squirrel-cage induction motor.

The stator is a stationary part and it has laminated construction, which is made up of stampings. These stampings consists of slots on its periphery to carry the stator winding. This winding is excited with a single phase AC supply.

The rotor is a rotating part and its construction is of squirrel cage type. The rotor consists of uninsulated aluminum or copper bars which are placed in the slots.

These rotor bars are permanently shorted at both ends with the help of end rings as shown in figure.

Squirrel cage rotar of a single phase induction motorwarum bleiben manche frauen single 472px" />
There is no physical connection between the stator and rotor, but there is a small and uniform gap between them.

The rotor acts as a conductor which when placed in the stator magnetic field, an emf is induced in it, produces its own magnetic field which further interacts with stator field to produce the torque.

Single phase induction motor constructionWhenever a single phase AC supply is given to the stator winding, an alternating magnetic field is produced around the stator.

Due to the pulsating nature of the field which reverses for every half-cycle, cannot produce rotation in a stationary squirrel cage rotor.

In case of three phase induction motor, the field produced by the supply is of rotating type and hence they are self starting motors.

But in case of single phase motors, the field produced by the stator is not rotating (but alternating only) and hence single phase motors are not self starting.

But, if the rotor is rotated by any other means (by hand or any tool), the induced currents in the rotor will assist with stator currents to produce revolving field. This field causes the motor to run in the direction it is started even with a single winding.

However, it is not possible to give initial rotation every time externally if the motors are attached to loads. This problem can be avoided by converting single phase motor into a two-phase motor temporarily in order produce revolving flux. This is achieved by providing a starting winding in addition to main or running winding.

The auxiliary or starting winding is made highly resistive whereas the main or running winding is made highly inductive.

Due to the large phase difference between these two, the torque produced by the rotor is high enough to start it. Once the motor reaches 75 percent of its speed, the auxiliary winding may be disconnected by a centrifugal switch and the motor able to run on a single main winding.

Single phase induction motors are used primarily for domestic and light-industrial applications where three-phase supply is generally not available.

Types of Single Phase Induction Motors

As mentioned above that, due to the rotating magnetic field of the stator, the induction motor becomes self starting. There are many methods of making a single phase induction motor as self starting one.

Based on the starting method, single phase induction motors are basically classified into the following types.

  1. Split-phase motor
  2. Capacitor start motor
  3. Permanent capacitor run motor
  4. Capacitor start capacitor run motor
  5. Shaded pole motor

The rotating magnetic field is produced when there are minimum two alternating fluxes, having a phase difference between them.

The resultant of these two fluxes produces a rotating flux which rotates in space in one particular direction. So in all the above methods or say types of induction motors, the additional flux other than main flux should have a certain phase difference with respect to main or stator flux.

If the phase difference is more, starting torque will be more. So the starting torque of the motor depends on the rotating magnetic field and thereby, additional means (whether it is an auxiliary winding or anything).

Once the motor picks up the speed, this additional winding is removed from the supply. This is the basic principle followed by all these types of single phase induction motors.

Let us discuss these types of motors in brief.

Split Phase Induction Motor

Split phase motors

This is one of the most widely used types of single phase induction motors. The essential parts of the split phase motor include main winding, auxiliary winding and a centrifugal switch.

This is the simplest arrangement to set up a rotating magnetic field by providing two winding on the same stator core as shown in figure.

Split phase induction motor circuit diagram

The auxiliary or starting winding carries a series resistance such that its impedance becomes highly resistive in nature.

It is not wound identical to the main winding but contains fewer turns of much smaller diameter as compared to main winding.

This will reduce the amount of start current lags the voltage. The main winding is inductive in nature in such that current lags the voltage by some angle. This winding is designed for the operation of 75 % of synchronous speed and above.

These two windings are connected in parallel across the supply. Due to the inductive nature, current through main winding lags the supply voltage by a large angle while the current through starting winding is almost in phase with voltage due to resistive nature.

Hence there exists a phase difference between these currents and thereby phase difference between the fluxes produced by these currents. The resultant of these two fluxes produce rotating magnetic field and hence the starting torque.

The centrifugal switch is connected in series with the starting winding. When the motor reaches 75 to 80 percent of synchronous speed, the centrifugal switch is opened mechanically and thereby auxiliary winding is out of the circuit. Therefore, the motor runs only with main winding.

Split phase motors give poor starting torque due to small phase difference between main and auxiliary currents. Also, the power factor of these motors is poor. These are mainly used for easily started loads such as blowers, fans, washing machines, grinders, etc.

Capacitor Start Induction Motor

This motor is similar to the split phase motor, but in addition a capacitor is connected in series to auxiliary winding. This is a modified version of split phase motor.

Since the capacitor draws a leading current, the use of a capacitor increases the phase angle between the two currents (main and auxiliary) and hence the starting torque. This is the main reason for using a capacitor in single phase induction motors.

Here the capacitor is of dry-type electrolytic one which is designed only for alternating current use. Due to the inexpensive type of capacitors, these motors become more popular in wide applications.

These capacitors are designed for definite duty cycle, but not for continuous use. The schematic diagram of capacitor start motor is shown in figure below.

Capacitor Start Induction Motor circuit diagram

The operation of this motor is similar to the split phase motor where the starting torque is provided by additional winding.

Once the speed is picked up, the additional winding along with capacitor is removed from the circuit with the help of centrifugal switch. But, the difference is that the torque produced by this motor is higher than split phase motor due to the use of capacitor.

Due to the presence of a capacitor, the current through auxiliary winding will leads the applied voltage by some angle which is more than that of split case type.

Thus, the phase difference between main and auxiliary currents is increased and thereby starting torque.

The performance of this motor is identical to the split phase motor when it runs near full load RPM. Due to the capacitor, the inrush currents are reduced in this motor.

These motors have very high starting torque up to 300% full load torque. However the power factor is low at rated load and rated speed.

Owing to the high starting torque, these motors are used in domestic as well as industrial applications such as water pumps, grinders, lathe machines, compressors, drilling machines, etc.

Permanent Capacitor Induction Motor

This motor is also called as a capacitor run motor in which a low capacitor is connected in series with the starting winding and is not removed from the circuit even in running condition. Due to this arrangement, centrifugal switch is not required.
Here the capacitor is capable of running continuously. The low value capacitor produces more leading phase shift bur less total starting current as shown in phasor diagram.

Hence, the starting torque produced by these motors will be considerably lower than that of capacitor start motor. The schematic circuit of this motor is shown in figure below.

Permanent Capacitor Induction Motor circuit diagram

 

In this, the auxiliary winding and capacitor remains in circuit permanently and produce an approximate two phase operation at rated load point. This is the key strength of these motors.

This will result better power factor and efficiency. However, the starting torque is much lower in these motors, typically about 80 percent of full load torque.

Due to the continuous duty of auxiliary winding and capacitor, the rating of these components should withstand running conditions and hence permanent capacitor motor is more than equivalent split phase or capacitor start motors. These motors are used in exhaust and intake fans, unit heaters, blowers, etc.

Capacitor Start and Capacitor Run Induction Motor

These motors are also called as two-value capacitor motors. It combines the advantages of capacitor start type and permanent capacitor type induction motors.

This motor consists of two capacitors of different value of capacitance for starting and running. A high value capacitor is used for starting conditions while a low value is used for running conditions.

Capacitor start and capacitor run motorIt is to be noted that this motor uses same winding arrangement as capacitor-start motor during startup and permanent capacitor motor during running conditions. The schematic arrangement of this motor is shown in figure below.

Capacitor start and capacitor run motor circuit diagram

At starting, both starting and running capacitors are connected in series with the auxiliary winding. Thus the motor starting torque is more compared with other types of motors.

Once the motor reaches some speed, the centrifugal switch disconnects the starting capacitor and leaves the running capacitor in series with auxiliary winding.

Thus, both running and auxiliary windings remain during running condition, thereby improved power factor and efficiency of the motor.

These are the most commonly used single phase motors due to high starting torque and better power factor. These are used in compressors, refrigerators, air conditioners, conveyors, ceiling fans, air circulators, etc.

Shaded Pole Induction Motor

This motor uses entirely different technique to start the motor as compared with other motors so far we have discussed now.

This motor doesn’t use any auxiliary winding or even it doesn’t have a rotating field, but a field that sweeps across the pole faces is enough to drive the motor. So the field moves from one side of the pole to another side of the pole.

Although these motors are of small ratings, inefficient and have low starting torque, these are used in a variety of applications due to its outstanding features like ruggedness, low initial cost, small size and simple construction.

A shaded pole motor consists of a stator having salient poles (or projected poles), and a rotor of squirrel cage type. In this, stator is constructed in a special way to produce moving magnetic field.

Stator poles are excited with its own exciting coils by taking the supply from a single phase supply. A 4-pole shaded pole motor construction is given in below figure.

Shaded pole induction motor constructionEach salient pole is divided into two parts; shaded and un-shaded. A shading portion is a slot cut across the laminations at about one third distance from one edge, and around this a heavy copper ring (also called as shading coil or copper shading band) is placed.

This part where shading coil is placed is generally termed as shaded part of the pole and remaining portion is called as un-shaded part as shown in figure.

Let us discuss how the sweeping action of the field takes place.

When an alternating supply is given to the stator coils, an alternating flux will be produced. The distribution of flux in the pole face area is influenced by the presence of copper shading band.

Let us consider the three instants, t1, t2, and t3 of alternating flux for an half cycle of the flux as shown in figure.

Shaded pole motor working

  1. At instant t= t1, the rate of change of flux (rising) is very high. Due to this flux, an emf is induced in the copper shading band and as the copper shading band is shorted, current circulates through it. This causes current to create its own field.According to Lenz’s law, the current through copper shading band opposes the cause, i.e., rise of supply current (and hence rise of main flux). Therefore the flux produced by shading ring opposes the main flux. So there is weakening of flux in the shaded part while crowding of flux in un-shaded part. So the axis of overall flux shifts to non-shaded part of the pole as shown in the figure.
  2. At instant t=t2, the rate of rise of flux is almost zero, and hence very little emf is induced in the shaded band. It results negligible shaded ring flux and hence there is no much affect on distribution of main flux. Therefore, the distribution of flux is uniform and the overall flux axis lies at the center of the pole as shown in figure.
  3. At instant t=t3, the rate of change of flux (decreasing) is very high, and induces emf in copper shading band. The flux produced by the shading ring is now opposes the cause according to Lennz’s law. Here, the cause is decreasing flux, and opposing means its direction is same as that of main flux. Hence, this flux strengthens the main flux. So there will be crowding of flux in the shaded part compared to the non shaded part. Due to this overall flux axis shifts to the middle of shaded part.This sequence will repeat for negative cycle too and consequently it produce moving magnetic field for every cycle from non shaded part of the pole to shaded part of the pole. Due to this field, motor produces the starting torque. This starting torque is low about 40 to 50 percent of full load torque. Therefore, these motors are used in low starting torque applications such as fans, toy motors, blowers, hair dryers, photocopy machines, film projectors, advertising displays, etc.

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Zahra Doejune 2, 2017
Morbi gravida, sem non egestas ullamcorper, tellus ante laoreet nisl, id iaculis urna eros vel turpis curabitur.
Zahra Doejune 2, 2017
Morbi gravida, sem non egestas ullamcorper, tellus ante laoreet nisl, id iaculis urna eros vel turpis curabitur.
Zahra Doejune 2, 2017
Morbi gravida, sem non egestas ullamcorper, tellus ante laoreet nisl, id iaculis urna eros vel turpis curabitur.

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