Title: Motor Starter Types and Technology And Its Applications
1Types And Technology of Motor Starter And
Applications
2Types 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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3Types And Technology of Motor Starter And
Applications
Block Diagram
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4Types 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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5Types And Technology of Motor Starter And
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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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6Types 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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7Types And Technology of Motor Starter And
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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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8Types And Technology of Motor Starter And
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Types of Motor Starters
- Direct On line
- Star Delta
- Auto Transformer starter
- Stator Resistance Starter
- Rotor Resistance Starter
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9Types 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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10Types And Technology of Motor Starter And
Applications
Direct On line
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11Types 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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12Types And Technology of Motor Starter And
Applications
Star Delta
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13Types And Technology of Motor Starter And
Applications
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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14Types And Technology of Motor Starter And
Applications
Auto Transformer starter
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15Types And Technology of Motor Starter And
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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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16Types And Technology of Motor Starter And
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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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17Types And Technology of Motor Starter And
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Application of Star Delta Starter to Control
Starting of Induction Motor
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18Types And Technology of Motor Starter And
Applications
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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19Types And Technology of Motor Starter And
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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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20Types And Technology of Motor Starter And
Applications
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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21Types And Technology of Motor Starter And
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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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22Types And Technology of Motor Starter And
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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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23Types And Technology of Motor Starter And
Applications
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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24Types 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
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25Types And Technology of Motor Starter And
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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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26Types And Technology of Motor Starter And
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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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27Types 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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28Types And Technology of Motor Starter And
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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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