Automatic Star Delta Starter using

Relays and Adjustable Electronic

Timer for Induction Motor

http://www.edgefxkits.com/

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:

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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

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

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.

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.

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Automatic Star Delta Starter using Relays and

Adjustable Electronic Timer for Induction Motor

Circuit Diagram:

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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.

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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.

http://www.edgefxkits.com/

Automatic Star Delta Starter using Relays and

Adjustable Electronic Timer for Induction Motor