Transcript star delta starter

ELECTRICAL
DEPARTMENT
ELEMENT OF
ELECTRIC DESIGN
PREPARED BY:
URVASHI GADHAVI(130040109521)
DEVANGI DHANDHUKIYA(130040109518)
STARTER
NEED OF STARTER
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If a rated stator voltage is applied to the motor at the time of starting,
then the motor will draw heavy starting current.
This will lead to excess i2R losses in the winding which will overheat
the motor.
Secondly due to a heavy current drawn from the AC supply voltage
will reduce.
The heavy starting current may damage the motor windings.
In order to avoid these problems, we can use some kind of a starter to
start the induction motor safely.
TYPES OF STARTER
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Auto transformer starting
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Star-delta starter
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Direct on line (DOL) starter
AUTO-TRANSFORMER
STARTER
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An autotransformer is used to apply a low voltage to the stator
winding at the time of starting. When the motor speed reaches
the desired level, autotransformer is disconnected and motor is
connected directly across the supply.
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The stator of the motor is connected through a 6-way
double throw switch.
While starting, the switch is thrown to ‘Start’ side so that a
reduced voltage is applied to stator. This keeps the starting
current safe limits.
Once motor take up the speed, the switch is throw to ‘Run’
side so that full supply voltage is applied to stator.
A specific advantage of this starter is that reduction in
voltage during starting, can be done to any desired level by
selecting proper tapping of the autotransformer.
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STAR DELTA STARTER
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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.
STAR-DELTA CONNECTION
IN MOTOR
STAR DELTA POWER
CIRCUIT
MOTOR STARTING
CHARACTERISTICS OF
STAR-DELTA STARTER:
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Available starting current: 33% Full Load Current.
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Peak starting current: 1.3 to 2.6 Full Load Current.
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Peak starting torque: 33% Full Load Torque.
ADVANTAGES OF STARDELTA STARTER:
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The operation of the star-delta method is simple and
rugged
It is relatively cheap compared to other reduced
voltage methods.
Good Torque/Current Performance.
It draws 2 times starting current of the full load
ampere of the motor connected
DISADVANTAGES OF STARDELTA STARTER:
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Low Starting Torque, only 33% starting torque
Break In Supply – Possible Transients
Six Terminal Motor Required (Delta Connected).
It requires 2 set of cables from starter to motor.
The delta of motor is formed in starter and not on motor
terminals.
Applications with a load torque higher than 50 % of the
motor rated torque will not be able to start using the
start-delta starter.
WIRING DIAGRAM OF
DOL STARTER:
MOTOR STARTING
CHARACTERISTICS ON DOL
STARTER:
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Available starting current: 100%.
Peak starting current:
6 to 8 Full Load Current.
Peak starting torque:
100%
ADVANTAGES OF DOL
STARTER:
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Most Economical and Cheapest Starter
Simple to establish, operate and maintain
Simple Control Circuitry
Easy to understand and trouble‐shoot.
It provides 100% torque at the time of starting.
Only one set of cable is required from starter to motor.
Motor is connected in delta at motor terminals.
DISADVANTAGES OF DOL
STARTER:
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It does not reduce the starting current of the motor.
High Starting Current: Very High Starting Current
(Typically 6 to 8 times the FLC of the motor).
Mechanically Harsh: Thermal Stress on the motor, thereby
reducing its life.
Voltage Dip: There is a big voltage dip in the electrical
installation
High starting Torque: Unnecessary high starting torque,
even when not required by the load.
SUITABILITY
DOL is Suitable for:
Small water pumps, compressors, fans and conveyor belts.
Motor rating up to 5.5KW
DOL is not suitable for:
The peak starting current would result in a serious voltage
drop on the supply system
Motor rating above 5.5KW
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APPLICATION
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Cane Carrier Drive,
Feeder Table Drive,
Milling Plant Drive,
Raw juice Pumps,
Sulphited Juice Pumps,
Molasses Pumps,
Injection Pumps,
Cooling Tower Pumps and
Centrifugals for a Sugar Curing and Chemical Dosing pump.
DIFFERENCE BETWEEN
DOL/STAR DELTA
/AUTOTRANSFORMER
Sr DOL Starter
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Star delta starter
Auto transformer
starter
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Used up to 5 HP
Used 5 HP to 20HP
Used above 20 HP
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Does not decrease
the starting current
Decreases the starting current
by 1/3 times
Decreases the starting
current as required
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It is cheap
It is costly
It is more costly
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It connects directly
the motor with
supply for starting
as well as for
running
It connects the motor first in
star at the time of starting in
delta for running
It connects the motor
according to the taping
taken out from the auto
transformer
THANK YOU