The document describes an automatic star-delta starter circuit for induction motors using relays and an adjustable electronic timer. The circuit starts the motor in star configuration using three transformers, rectifiers and a 555 timer circuit to control four relays. After a preset time, the fourth relay switches the motor to delta configuration. It provides basic protection from voltage fluctuations and single phasing faults. The starter reduces starting current compared to direct online starting and is a low-cost solution, though it can be improved further with soft start capabilities.

1. Automatic Star Delta Starter using
Relays and Adjustable Electronic
Timer for Induction Motor

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Automatic Star Delta Starter using Relays and
Adjustable Electronic Timer for Induction Motor
Introduction:
 Induction motors are popular due to their low-cost, sturdy construction,
fast pick-up, low maintenance expenditure and real efficiency.
 The DOL (direct-on-line) starters and star/delta starters used for starting
and running of induction motors provide coarse type of protections
against voltage fluctuations and single phasing.
 Induction motors are very sensitive to low voltage and single phasing
during which they draw a heavy current and can burn out unless
switched of within few seconds of occurrence of such conditions

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Automatic Star Delta Starter using Relays and
Adjustable Electronic Timer for Induction Motor
 An Induction or asynchronous motor is a type of AC motor where
power is supplied to the rotor by means of electromagnetic induction,
rather than a commutator or slip rings as in other types of motor
 These motors are widely used in industrial drives, particularly poly -
phase induction motors because they are rugged and have no brushes.
 Their speed is determined by the frequency of the supply current, so
they are most widely used in constant-speed applications, although
variable speed versions, using variable frequency drives are becoming
more common.

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Automatic Star Delta Starter using Relays and
Adjustable Electronic Timer for Induction Motor
Block Diagram:

5. http://www.edgefxkits.com/
Automatic Star Delta Starter using Relays and
Adjustable Electronic Timer for Induction Motor
Hardware Requirements:
 Power Supply Block
 Relay
 Induction Motor
 555 Timer
 Bc 547 Transistor
 Bc 558
 In4007 Rectifier Diode
 Led
 RESISTORS And CAPACITORS

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Automatic Star Delta Starter using Relays and
Adjustable Electronic Timer for Induction Motor
555 TIMER:
 The 555 Timer IC is an integrated circuit (chip) implementing a variety
of timer and multivibrator applications.
 The original name was the SE555 (metal can)/NE555 (plastic DIP), and
the part was described as "The IC Time Machine".
 Depending on the manufacturer, the standard 555 package includes over
20 transistors, two diodes, and 15 resistors on a silicon chip installed in
an 8-pin mini dual-in-line package (DIP-8).

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Automatic Star Delta Starter using Relays and
Adjustable Electronic Timer for Induction Motor
Pin Diagram Of 555:
The 555 timer IC is a mere eight pin DIL
package IC. It can be
 Used as a monostable.
 Source or sink 100mA.
 Use supply voltages of 5v to 15v.
 Disrupt the power supply - use a decoupling
capacitor.

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Automatic Star Delta Starter using Relays and
Adjustable Electronic Timer for Induction Motor
Stator and Rotor:
 The stator winding consists of three different windings which overlap one
another and are offset by an electrical angle of 120°.
 Synchronous Speed (Ns) = 60; f/p.
 Ns= Synchronous Speed/ minute;
 F= frequency;
 P=Pole pair Number;
Rotor in induction machines with squirrel-cage rotors consists of a slotted
cylindrical rotor core sheet package with aluminum bars which are joined at
the front by rings to form a closed cage.

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Automatic Star Delta Starter using Relays and
Adjustable Electronic Timer for Induction Motor

10. http://www.edgefxkits.com/
Automatic Star Delta Starter using Relays and
Adjustable Electronic Timer for Induction Motor
BC547:
 The BC547 transistor is an NPN Epitaxial Silicon Transistor.
 The BC547 transistor is a general-purpose transistor in small plastic
packages.
 It is used in general-purpose switching and amplification
BC847/BC547 Series 45 V, 100 mA NPN general purpose transistors.
 Whenever the base is high, then current starts flowing through base and
emitter and after that only current will pass from collector to emitter.

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Automatic Star Delta Starter using Relays and
Adjustable Electronic Timer for Induction Motor

12. http://www.edgefxkits.com/
Automatic Star Delta Starter using Relays and
Adjustable Electronic Timer for Induction Motor
BC558:
 The BC557 transistor is a PNP Epitaxial Silicon Transistor.
 The BC557 transistor is a general-purpose transistor in small plastic
packages. It is used in general-purpose switching and amplification
BC847/BC547 Series 45 V, 100 mA PNP general-purpose transistors.

13. http://www.edgefxkits.com/
Automatic Star Delta Starter using Relays and
Adjustable Electronic Timer for Induction Motor
Relay:
 It is an electromagnetic switch.
 Used to control the electrical devices.
 Copper Core Magnetic Flux plays a primary role
here.

14. http://www.edgefxkits.com/
Automatic Star Delta Starter using Relays and
Adjustable Electronic Timer for Induction Motor
Circuit Diagram:

15. http://www.edgefxkits.com/
Automatic Star Delta Starter using Relays and
Adjustable Electronic Timer for Induction Motor
Circuit Explanation:
 Star – Delta starter generally comprises of contactors and an adjustable
timer to enable starting of the induction motor in star mode and then
switch over to Delta Mode after the preset time so decided by the timer.
 This uses three step-down transformers, the primary of which are
connected in star mode while their secondary develop filtered dc after
passing through respective bridge rectifiers and filter capacitors out of
the three. Such dc derived one dc is used for a timer circuit built around
a 555 timer wired in a stable mode but operating in monostable mode.
 Two other dc supplies operate the two relays. These two are connected
in series with the third relay coil. Mains of the three phases are
connected to the third relay.

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Automatic Star Delta Starter using Relays and
Adjustable Electronic Timer for Induction Motor
 Fourth relay takes star to the delta conversion care.
 The timer operates this fourth relay.
 Single phasing meaning any one or two phases Y & B missing bring
either relay – 1 or relay - 2 to off condition that results in the relay – 3
to switch Off.
 At starting due to the connection of the fourth relay in star, the motor
begins as star connection
 After the time elapsed by the timer operates the fourth relay coil. The
relay switches Delta mode. It also gives the indication in which mode
the motor is running by LED.

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Automatic Star Delta Starter using Relays and
Adjustable Electronic Timer for Induction Motor
Future Scope:
 Compared to the reduced voltage methods it is the simple and cheapest
way of starting the motor.
 But it takes significant inrush currents during the switching operation.
 Further the project can be enhanced by using thermistors in firing angle
control principle for soft start of the induction motor that would
overcome all the drawbacks of star delta starter.

18. http://www.edgefxkits.com/
Automatic Star Delta Starter using Relays and
Adjustable Electronic Timer for Induction Motor
Conclusion:
 An automatic over and under voltage protector system has been
implemented using induction motor starter which is necessitated by the
need to monitor the voltage supply to the equipment and appliances.
Consequently, protect them from the danger of being damaged due to
voltage fluctuation.
 This type of starting is used for low to medium voltage and light
starting torque motors.
 It is the cheapest way to reduce the starting current, and it is in the order
of 3-4 times that in case of direct online starting of induction motor.

19. http://www.edgefxkits.com/
Automatic Star Delta Starter using Relays and
Adjustable Electronic Timer for Induction Motor