motor starter types and technology of motor starter and its applications
DESCRIPTION
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.TRANSCRIPT
Types And Technology of
Motor Starter And Applications
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Types And Technology of Motor Starter And
ApplicationsIntroduction: 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
ApplicationsBlock Diagram
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Types And Technology of Motor Starter And
ApplicationsNeed 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
ApplicationsNeed 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
ApplicationsDefinition 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
ApplicationsPrinciple 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
ApplicationsTypes 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
ApplicationsDirect 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
ApplicationsDirect On line
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Types And Technology of Motor Starter And
ApplicationsStar 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
ApplicationsStar Delta
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Types And Technology of Motor Starter And
ApplicationsAuto 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
ApplicationsAuto Transformer starter
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Types And Technology of Motor Starter And
ApplicationsStator 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
ApplicationsRotor 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
ApplicationsApplication of Star Delta Starter to Control Starting of Induction Motor
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Types And Technology of Motor Starter And
ApplicationsApplication 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
ApplicationsApplication 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
ApplicationsSoft 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
ApplicationsSoft 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
ApplicationsSoft 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
ApplicationsTechnology 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
ApplicationsVoltage 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
ApplicationsUse 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
ApplicationsAdvantages
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
ApplicationsDisadvantages
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
ApplicationsConclusion
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.
