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shaded pole single phase induction motor ppt

Shaded Pole Induction Motor

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Definition: The shaded pole induction motor singlehoroskop steinbock august 2016 is simply a self-starting single-phase induction motor whose one of who is aubrey o'day dating 2015 the pole is shaded by the copper who is aubrey o'day dating 2015 ring. The copper ring is also called the shaded ring. This copper ring act as a secondary winding for the motor. The shaded pole motor rotates only in one particular direction, and the reverse movement of the motor is not possible.

Why the Shaded Pole Induction Motor designs for low power rating?

The power losses are very high in the shaded pole induction motor. And the power factor of the motor is low. The starting torque induces in the induction motor are also very low. Because of the following reasons the motor has poor efficiency. Thus, their designs are kept small, and the motor has low power ratings.

Construction of Shaded Pole Induction Motor

The shaded pole motor may have two or four poles. Here in this article, we use the two pole motor for the sake of simplicity. The speed of the motor is inversely proportional to billy bob thornton dating halle berry the number of poles used in the motor.

Stator – The stator of the shaded pole motor has a salient pole. The salient pole means the poles of the magnet are projected towards the armature of the motor. Each pole of the motor is excited by its exciting coil. The copper rings shade the loops. The loops are known as the shading coil.

The poles of the motor are laminated. The lamination means multiple layers of material are used for making the poles. So, that the strength of the pole increases.

The slot is constructed at some distance apart from the edge of the poles. The short-circuited copper coil is placed in this slot. The part which is covered with the copper ring is called the shaded part and which are not covered by the rings are called unshaded part.

Rotor – The shaded pole motor uses the squirrel cage rotor. The bars of the rotor is skewed at an angle billy bob thornton dating halle berry of 60º. The skew can be done for obtaining the better starting torque.

The construction of the motor is very simple because it does not contain any commutator, brushes, collector rings, etc. or any other part. The shaded pole induction motor does not have any centrifugal switch. Thus, the chances of failure of the motor are less.

The centrifugal switch is the type of electrical switch that starts operating by using the centrifugal force, generated by the rotating shaft. It is also used for controlling the speed of the shaft.

Shaded Pole Induction Motor Working

When the supply is connected to the windings of the rotor, the alternating flux billy bob thornton dating halle berry induces in the core of the rotor. The small portion of the flux link with the shaded coil of the motor as because it is short-circuited. The variation in the flux induces the voltage inside the ring because of which the circulating current induces in it.

The circulating current develops the flux in the ring which opposes the main flux of the motor. The flux induces in the shaded portion of the motor, i.e., a and the unshaded portion of the motor, i.e., b have a phase difference. The main motor flux and the shaded ring flux are also having a space displacement by an angle of 90°.

The connection diagram of the Shaded Pole Motor is shown below.

Shaded pole induction motor figAs there is time and space displacement between the two fluxes, the rotating magnetic field induces in the coil. The rotating magnetic field develops the starting torque in the motor. The field rotates from the unshaded portion to the shaded portion of the motor.

Applications of the Shaded Pole Induction Motor

The various applications of the Shaded Poles Motor are as follows:-

  • They are suitable for small devices like relays and fans because of its low cost and easy starting.
  • Used in exhaust fans, hair dryers and also in table fans.
  • Used in air conditioning and refrigeration equipment and cooling fans.
  • Record players, tape recorders, projectors, photocopying machines.
  • Used for starting electronic clocks and single-phase synchronous timing motors.

This type of motor is used to drive the devices which require low starting torque.


who is aubrey o'day dating 2015 Title: Single Phase Induction


1
Single Phase Induction

  • Permanent-split capacitor motor

One way to solve the single phase problem is to
build a 2-phase motor, deriving 2-phase power
from single phase. This requires a motor with two
windings spaced apart 90o electrical, fed with
two phases of current displaced 90o in time. This
is called a permanent-split capacitor motor in
Figure
2
Main and Auxiliary windings
3
1-Phase 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.

4
1-Phase Induction Motor
  • This motor configuration works well up to 1/4
    sächsische zeitung er sucht sie /> horsepower (200watt), though, usually applied to
    smaller motors. 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

5
Capacitor-start induction motor
In Figure 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.
6
Capacitor-run motor induction motor
A variation of the capacitor-start motor Figure
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.
7
1-phase Capacitor start
8
Capacitor Start-Run Induction Motor
  • A motor starting capacitor may be a double-anode
    non-polar electrolytic capacitor which could be
    two to (or - to -) series connected polarized
    electrolytic capacitors. 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.

9
Resistance split-phase motor induction motor
If an auxiliary winding of much fewer turns of
smaller wire is placed at 90o electrical to the
main winding, it can start a single phase
induction motor. With lower inductance and higher
resistance, the current will experience less
phase shift than the main winding. About 30o of
phase difference may be obtained. This coil
produces a moderate starting torque, which is
disconnected by a centrifugal switch at 3/4 of
synchronous speed. This simple (no capacitor)
arrangement serves well for motors who is aubrey o'day dating 2015 up to 1/3
horsepower (250 watts) driving easily started
loads.
10
Wound rotor induction motors
A wound rotor induction motor has a stator like
the squirrel cage induction motor, but a rotor
with insulated windings brought out via slip
rings and brushes. However, no power is applied
to the slip rings. Their sole purpose is to allow
resistance to be placed in series with the rotor
windings while starting.
This resistance is shorted out once the motor is
started to make the rotor look electrically like
the squirrel cage counterpart.
11
Wound Rotor Induction M/C
  • Why put resistance in series with the rotor?
    Squirrel cage induction motors draw 500 to over
    1000 of full load current (FLC) during starting.
    While this is not a severe problem for small
    motors, it is for large (10's of kW) motors.
    Placing resistance in series with the rotor
    windings not only decreases start current, locked
    rotor current (LRC), but also increases the
    starting torque, locked rotor torque (LRT).

12
Wound Rotor Induction M/C
  • Figure shows that by increasing the rotor
    resistance from R0 to R1 to R2, the breakdown
    torque peak is shifted left to zero speed. Note
    that this torque peak is much higher than the
    starting torque available with no rotor
    resistance (R0) Slip is proportional to rotor
    resistance, and pullout torque is proportional to
    slip. Thus, high torque is produced while
    starting.

13
Wound Rotor Induction M/C
14
Wound Rotor Induction M/C
  • The resistance decreases the torque available at
    full running speed. But that resistance is
    shorted out by the time the rotor is started. A
    shorted rotor operates like a squirrel cage
    rotor. Heat generated during starting is mostly
    dissipated external to the motor in the starting
    resistance. The complication and maintenance
    associated with brushes and slip rings is a
    disadvantage of the wound rotor as compared to
    the simple squirrel cage rotor.

15
Wound Rotor Induction
  • This motor is suited for starting high inertial
    loads. A high starting resistance makes the high
    pull out torque available at zero speed. For
    comparison, a squirrel cage rotor only exhibits
    pull out (peak) torque at 80 of its' synchronous
    speed

16
Speed Control
  • Motor speed may be varied by putting variable
    resistance back into the rotor circuit. This
    reduces rotor current and speed. The high
    starting torque available at zero speed, the down
    shifted break down torque, is not available at
    high speed. See R2 curve at 90 Ns, Resistors
    R0R1R2R3 increase in value from zero. A higher
    resistance at R3 reduces the speed further. Speed
    regulation is poor with respect to changing
    torque loads. This speed control technique is
    only useful over a range of 50 to 100 of full
    speed. Speed control works well with variable
    speed loads like elevators and printing presses.

17
Speed Control
18
  • Shaded Pole Induction Motor

Main windings and Shaded Pole winding at the
Stator, while shaded pole is short circuited.
19
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20
Repulsion Motor
The machine is often converted into an induction
motor during the period of running by arranging
that all the commutator segments are
short-circuited by a centrifugally-operated
device when the motor is up to speed. The brushes
are also lifted in same cases to reduce wear. To
avoid the complication of the short-circuiting
device, the rotor may be arranged with a
squirrel-cage winding at the bottom of the slots.
This takes over at speed and gives
induction-motor characteristics
21
Reversal of Rotation is achieved by switching on
rotor windings
22
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Universal Motors

A universal motor is a single-phase series motor, which is able to run on either alternating current (ac) or direct current (dc) and the characteristics are similar for both ac and dc. The field windings of a series motors are connected in series with the armature windings

 
Basic principles of Universal Motors

The electrical design areas of a universal motor are the magnetic circuit, the field and armature windings, the commutator and brushes, the insulation and the cooling system.

 
Commutation Process of Universal Motors

 
Performance Characteristics of Universal Motors

Shaded Pole Motors

A Shaded Pole motor is an AC single phase induction motor. The auxiliary winding, which is composed of a copper ring, is called a shading coil. The current in this coil delay the phase of magnetic flux in that part of the pole in order to provide a rotating magnetic field. The direction of rotation is from the unshaded side to the shaded ring.

 
Basic principles of Shaded Pole Motor

  • This shading-coil (ring) arrangement displaces the axis of the shaded poles from the axis of the main poles
  • When power is applied to the stator, the flux in the main part of the pole induces a voltage in the shading coil, which acts as a transformer secondary winding.
  • Since the current in the secondary winding of a transformer is out of phase with the current in the primary winding.
  • The current in the shading coil is out of phase with the current in the main field winding.
  • Thus, the flux of the shading pole is out of phase with the flux of the main pole.

 
Rotating field of a Shaded Pole Motor

Synchronous Motors

Synchronous ac motors are constant-speed electric motors and they operate in synchronism with line frequency. The speed of a synchronous motor is determined by the number of pairs of poles and is always a ratio of the line frequency.

  • The stator is provided with two simple coils, which can be directly connected to the mains.
  • The rotor consists of a cylindrical permanent two-pole magnet, which is diametrically magnetized.

 
Basic principles of Synchronous Motors
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Zahra Doejune 2, 2017
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Zahra Doejune 2, 2017
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Zahra Doejune 2, 2017
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