Motor Starter Types and Technology And Its Applications - PowerPoint PPT Presentation

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Motor Starter Types and Technology And Its Applications

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Most induction motors are started directly on line, but when very large motors are started that way, they cause a disturbance of voltage on the supply lines due to large starting current surges. To limit the starting current surge, large induction motors are started at reduced voltage and then have full supply voltage reconnected when they run up to near rotated speed. – PowerPoint PPT presentation

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Title: Motor Starter Types and Technology And Its Applications


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Types And Technology of Motor Starter And
Applications
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Types And Technology of Motor Starter And
Applications
Introduction
  • An induction motor is a 3 phase motor consisting
    of the 3 phase winding as the stator with a
    permanent magnet and the rotor as another 3 phase
    windings. It works on the principle of rotating
    magnetic field, i.e. the formation of the
    magnetic flux from 3 phase winding fluxes, which
    rotates about its axis, causing the rotor to
    rotate.

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Types And Technology of Motor Starter And
Applications
Block Diagram
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Types And Technology of Motor Starter And
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Need for Motor Starting
  • In an induction motor, when supply is given to
    the stator windings.
  • The rotating magnetic field flux and the produced
    flux in the rotor windings due to the back emf.
  • It causes the motor torque to increase, causing a
    high rotor current. 
  • During the time between the application of
    electric supply to the motor and the actual
    acceleration of the motor to its full speed.
  • A large amount of current is drawn by the stator
    from the supply. 

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Types And Technology of Motor Starter And
Applications
Need for Motor Starting
  • This starting current is about 5 to 6 times more
    than the full load current.
  • This time duration can be for few seconds or
    longer.
  • This causes the electrical equipments to damage
    because of the increasing voltage drop in
    electrical systems.
  • Due to flow of larger currents across the cable. 
  • For this reason, a definite method of starting
    the motor is needed.

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Types And Technology of Motor Starter And
Applications
Definition of Motor Starter
  • It is the device connected in series with the
    motor to decrease its starting current and then
    increase it as the motor starts rotating
    gradually.
  • It consists of a connector which acts as a
    switch to control flow of current to the motor
    and a overload unit which measures the flow of
    current through the motor and controls the
    halting of motor in case of large current being
    drawn.

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Types And Technology of Motor Starter And
Applications
Principle of Motor Starter
  • The current drawn by the motor can be controlled
    by reducing the back emf (possible by reducing
    the supply voltage) or by increasing the rotor
    resistance during the motor starting.

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Types And Technology of Motor Starter And
Applications
Types of Motor Starters
  • Direct On line
  • Star Delta
  • Auto Transformer starter
  • Stator Resistance Starter
  • Rotor Resistance Starter

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Types And Technology of Motor Starter And
Applications
Direct On line
  • It consists of simple push button as the
    controller. 
  • When the start button is pressed.
  • The switch connecting the motor and the main
    supply is closed and the motor gets the supply
    current. 
  • In case of over current, the stop button is
    pressed and the bypass auxiliary contact is
    opened.

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Types And Technology of Motor Starter And
Applications
Direct On line
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Types And Technology of Motor Starter And
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Star Delta
  • The 3 windings are first connected in star
    connection.
  • After some time (decided by the timer or other
    controller circuit) the windings are connected in
    delta connection.
  • In star connection, the current drawn is 0.58 of
    the normal current and also the phase voltage is
    reduced to 0.58. 
  • Thus the torque is reduced.

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Types And Technology of Motor Starter And
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Star Delta
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Types And Technology of Motor Starter And
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Auto Transformer starter
  •  It consists of an auto transformer in star
    connection.
  • It reduces the voltage applied to the motor
    terminals. 
  • It consists of 3 tapped secondary coils connected
    to the three phases.
  • In the starting period the transformer allows
    application of lower voltages to the three
    windings.

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Types And Technology of Motor Starter And
Applications
Auto Transformer starter
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Types And Technology of Motor Starter And
Applications
Stator Resistance Starter
  • It consists of three resistors in series with
    each phase of the stator windings.
  • It causes a voltage drop across each resistor and
    as a result a low voltage is applied to each
    phase.

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Types And Technology of Motor Starter And
Applications
Rotor Resistance Starter
  • It consists of 3 resistances connected in series
    with the rotor windings, thus reducing the rotor
    current, but increasing the torque.

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Types And Technology of Motor Starter And
Applications
Application of Star Delta Starter to Control
Starting of Induction Motor
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Types And Technology of Motor Starter And
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Application of Star Delta Starter to Control
Starting of Induction Motor
  • The star delta starter is the cheapest among all
    the starters and is suitable for applications
    like machine tools, pumps, motor generators etc.
  • A star delta starter can be used in starting an
    induction motor by using 2 relays as the
    connector and the timer as the controller.
  • 1 connector is used to provide the mains supply
    while the other connector controls the connection
    of motor in star or delta connection.
  • Transformers are used, primaries of which are
    connected to the 3 phase supply and the
    secondaries are connected to the relays and the
    timer.

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Types And Technology of Motor Starter And
Applications
Application of Star Delta Starter to Control
Starting of Induction Motor
  • The two relays are used to trigger the timer,
    which develops a high logic output at pin 3.
  •  Thus switching on the relay 4, causing the
    supply in star connection
  • It offers low power intensity to the load by
    isolating the load from the normal 3 phase supply
    through relay 3.
  • Some more regarding this starting of induction
    discussed below.

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Types And Technology of Motor Starter And
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Soft Start of Induction Motor by Stepped Delay of
Reducing Firing Angle
Soft Start and Soft Stop
  • In normal start up of the induction motor, more
    torque is developed.
  • It causes the stress to be transferred to the
    mechanical transmission system.
  • It results in excessive wear and failure of the
    mechanical parts. 
  • As acceleration increases, high current is drawn
    which is about 600 of the normal run current.
  • This can be seldom solved using a star delta
    starter

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Types And Technology of Motor Starter And
Applications
Soft Start and Soft Stop
  • Soft start provides a reliable and economical
    solution to these problems by delivering a
    controlled release of power to the motor, thereby
    providing smooth, steeples acceleration and
    deceleration. The damage to windings and bearings
    are reduced, resulting in an extended motor life.

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Types And Technology of Motor Starter And
Applications
Soft Start and Soft Stop
  • With this technique, a controlled starting and
    stopping is achieved with proper selection of
    ramp times and setting of the current limit.
  • Less mechanical stress.
  • Improved power factor.
  • Lower maximum demand.
  • Less mechanical maintenance.
  • This technique is suitable for applications where
    torque transients are frequent, such as in
    pumping fluids, which can ultimately lead to
    rupture pipes and couplings.

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Types And Technology of Motor Starter And
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Technology followed in Soft Starter
  • A soft starter is a type of reduced voltage
    starter for AC induction motors.
  • The soft starter is similar to a primary
    resistance or primary reactant starter in that it
    is in series with the supply to the motor.
  •  The input current to the started equals its
    output current.
  • It consists of solid state devices to control the
    current flow and the voltage applied to the
    motors.
  • The soft starters can be connected in series with
    the line voltage or connected inside the delta
    loop.

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Types And Technology of Motor Starter And
Applications
Voltage Control
  • Solid state AC switches are arranged in series
    with one or more phases to achieve voltage
    control.

Use of Solid state switches
  • 1 x Triac per phase

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Types And Technology of Motor Starter And
Applications
Use of Solid state switches
  • 1 x SCR and 1 x Diode reverse parallel connected
    per phase.
  • 2 x SCRs reverse parallel connected per phase.

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Types And Technology of Motor Starter And
Applications
Advantages
  • Star-Delta starters are widely used due to their
    relatively low price.
  • There are no limits to the number of times they
    can be operated.
  • The components require very little space.
  • The starting current is reduced to approximately
    one-third.

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Types And Technology of Motor Starter And
Applications
Disadvantages
  • The starter can only be applied to motors where
    the six leads or terminals can be accessed.
  • The supply voltage must be the same as the rated
    motor voltage for Delta connection.
  • Because the starting current is reduced to
    approximately one-third of the rated current, the
    starting torque is also reduced to one-third.
  • If the motor does not reach at least 90 of its
    rated speed at the time of switching from Star to
    Delta the current peak will be as high as in a
    D.O.L.

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Types And Technology of Motor Starter And
Applications
Conclusion
  • Most induction motors are started directly on
    line, but when very large motors are started that
    way, they cause a disturbance of voltage on the
    supply lines due to large starting current
    surges. To limit the starting current surge,
    large induction motors are started at reduced
    voltage and then have full supply voltage
    reconnected when they run up to near rotated
    speed.

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