Industrial Star Delta Starter for a 3-Phase Induction Motor

Industrial Star Delta Starter For
a 3-Phase Induction Motor

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Industrial Star Delta Starter for a 3-Phase
Induction Motor
Introduction Of Induction Motor?
 The most basic feature of an Induction motor is its self starting mechanism.
Due to the rotating magnetic field, an emf is induced in the rotor, because of
which current starts flowing in the rotor. As per the Lenz law, the rotor will
start rotating in a direction so as to oppose the flow of electric current and this
gives a torque to the motor. Thus the motor gets self started.

Induction Motor
Connection Of A 3 Phase Induction Motor Consists Of?
 A 3 Phase Induction motor consists of a stator.
 It contains 3 phase winding connected to the 3 phase AC supply.
 The arrangement of the winding is to produce a rotating magnetic field.
 The rotor of the Induction motor contains cylindrical core with parallel slots
that contain conductors.

Induction Motor
What Problems Can Encounter During Motor Starting?
 During the motor self starting period, torque increases and a large amount of
current flows in the rotor.
 To achieve this the stator draws a large amount of current and by the time the
motor reaches its full speed
 A large amount of current is drawn and coils get heated up, damaging the
motor.
 Hence there is a need to control the motor starting.
 One way is to reduce the applied voltage, which in turn reduces the torque.

Induction Motor

Induction Motor
The Objectives of Star-Delta Technique Motor Starter are
 Reduce high starting current and along these lines forestall motor from overheating.
 Provide over-burden and no-voltage assurance.

Induction Motor
Star Delta Starter:
 In star delta starting, the motor is connected in STAR mode throughout the
starting period. When the motor reached the required speed, the motor is
connected in DELTA mode.

Induction Motor
Main Components of a Star-Delta Starter
Contactors : The Star- Delta starter circuit comprises of three contactors: Main,
star and delta contactors.
Timer: The contactors are regulated by a timer incorporated with the started.
Interlock Switches: Interlock switches are connected between star and delta
contactors of the control circuit as a safety measure so one can’t activate delta
contactor without deactivating star contactor.
Thermal Overload Relay: A thermal over-load relay is likewise consolidated
into star-delta control circuit to ensure the motor from intemperate heat which
might expedite motor finding fire or wearing out.

Induction Motor
Working of Star-Delta Starter
 At first the primary contactor and the star contactors are shut.
 After a time interval the timer signs to the star contactor to head off to the
open position.
 The primary, delta contactors to head off to the shut position, accordingly
structuring delta circuit.
 At the time of starting, every stator stage gets voltage VL/v3, where VL is
the line voltage.
 The line current drawn by the motor at starting is decreased to one-third as
contrasted with starting current with the windings associated in delta.

Induction Motor
 Since the torque advanced by an induction motor is corresponding to the square of the
applied voltage.
 Star- delta starter decreases the starting torque to one- third of that possible by immediate
delta starting.
 The timer controls conversion from star connection to delta connection.
 A timer in star delta starter for a 3-phase motor is intended to do the move from star mode.
 Utilizing which the motor runs on a decreased voltage and current and produces less torque.
 To the delta mode indispensible for running the motor at its full power.
 Utilizing high voltage and current to transform a high torque.

Induction Motor
Terminal Connections in Star and Delta Configurations
Star Configuration:
 L1, L2 and L3 are the 3-phase line voltages, which are given to primary
contactor
 The main motor coils are U, V and W.
 In star mode of motor windings, the primary contactor associate the mains to
essential winding terminals U1, V1 and W1.
 The star contactor shorts the auxiliary winding terminals U2, V2 and W2

Induction Motor
 Notwithstanding when the primary contactor is shut, supply arrives at terminals
A1, B1, C1.
 Consequently the motor windings are energized in star-mode.
 The timer is initiated in the meantime moment when star contactor is energized.
 After the timer achieves the specified time period.
 The star contactor is de-energized and delta contactor is energized.
Star Configuration:

Induction Motor
The point when delta contactor closes.
 The motor winding terminals U2, V2 and W2 get associated with V1, W1 and
U1 individually through the shut contacts of primary contactor.
 For delta association, fulfilling end of one winding is to be joined with
beginning end of the other winding.
 The motor windings are reconfigured in delta by supplying line voltage L1 to
winding terminals W2 and U1, line voltage L2 to winding terminals U2 and
V1.
 The line voltage L3 to winding terminals V2 and W1.

Induction Motor
Induction Motor Winding Terminals Connected in Star
and Delta Configuration

Induction Motor
Types of Star Delta Starter
 There are two types of star-delta starters
 Open
 Close

Induction Motor
Star Delta Open Transition Starter
 It is the most widely recognized strategy for star-delta starting.
 In this strategy motor windings are open throughout the transition time of
altering the windings from a star mode with a delta mode.
 The star-delta open move starter uses 3 motor contactors and a move delay relay.

Induction Motor
Merits:
Open transition starter is very easy to implement in terms of cost and circuitry.
It does not require additional voltage educing equipment.

Induction Motor
Demerits:
 Open transition makes a surge of current and torque at change over
 Which stuns the system both electrically and mechanically.
 Electrically, the outcome of the momentary peaks in current could cause force
vacillations or misfortunes.
 Mechanically, the expanded torque coming about because of the current spike
could be sufficient to harm system components i.e. snap a drive shaft.

Induction Motor
Star Delta Closed Transition Starter:
 The transfer from the star to delta modes is made without disengaging motor
from the line.
 A couple of components are added to dispose of or decrease the surge
connected with the open transition.
 The extra components incorporate a contactor and few transition resistors.
 The transition resistors consume the present stream throughout the winding
changeover.

Induction Motor
 A fourth contactor is additionally used to place the resistor in circuit
before opening the star contactor.
 Afterward evacuating the resistors once the delta contactor is closed.
 The control circuit is more confounded because of the need to complete
resistor exchanging.

Induction Motor
Merit:
 There is a reduction in the incremental current surge, which results from transition.
 Thus closed transition starter has a smooth change over.

Induction Motor
Demerit:
 In addition to requiring more switching devices.
 The control circuit is more complicated due to the need to carry out resistor
switching.
 The added circuitry leads to significant rise in the cost of the installation.

Induction Motor
Full load current in Open Transition and Closed Transition

Induction Motor
Block Diagram

Induction Motor
Formula

Industrial Star Delta Starter for a 3-Phase Induction Motor

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