ATS_Writeup.81183803

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Enerco Energy Solutions LLP www.econserve.in

AN INTRODUCTIONTO THE FULLY AUTOMATIC LOW STARTING CURRENT, CONTINUOUS TORQUE

STARTERS WITH KORNDORFER CLOSED TRANSITION FOR SQUIRREL - CAGE

INDUCTION MOTORS

THE AUTO-STRESTERAUTO-STRESTER is a fully automatic low starting current starter, which is having the followingadvantages over &

above the other starters :

The Auto-Strester does not carry any handle. To start your Squirrel cage induction motor

just one push button is required to be pressed - that is all.

The greatest advantage of the Auto-Strester is that it draws less starting current from the

MAINS and

delivers simultaneously more current to the motor for the proper operation & quicker

acceleration of a Squirrel cage motor.

The Auto-Strester motor starter can limit the starting current of a Squirrel cage induction

motor to any desired value- depending upon the rules & regulations of the individual Supply

Authorities.

The life of the contacts of the Auto-Strester (contactors type starter) is much more as it

incorporates only automatic contactors.

The Auto-Strester can be Switched ON / Switched OFF by any nos. of Remote-control

stations.

The main advantage of the Auto-Strester is that because of its low starting current, one can

adjust the over load relay too close to the normal load of the motor & as such it will trip-off

itself whenever theres overloading / single-phasing, etc.

In our Auto-Strester we use Siemens / L&T / Schneider / C-H / Jyoti make Contactors, Over

load relay, & Time delay relays etc.

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Auto-Strester is Guaranteed for two years against any Technical- defect / bad

workmanship.

SALIENT FEATURES: Easy operation.

Time tested.

Complying with the requirements specified as per IEC : 947, IS : 3914 & IS : 8544 (Part 4).

Comprehensive range.

Maintenance of Motor starters is very easy. Everything is front Operated.

Wall Mounting Design upto 75 HP & Floor Mounting Design 80 HP& above.

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STARTING METHODS OF SQUIRREL CAGE INDUCTION MOTORS :

The cheapest drive in the world is a drive operated Electrically i.e. an Electric - Motor. There are

different types of Electric-motors available in the market, but the cheapest, simple & robust out ofthe whole lot is a Squirrel cage induction motor. This type of motor has got very many advantages if

compared with that of a similar electric motor having wound rotor.

The initial cost of the installation of a motor having wound rotor (slip- ring ) is practically double if

compared with that of an ordinary Squirrel cage induction motor & moreover the running

maintenance of a motor having wound rotor is too high i.e. it requires the cleaning / replacement

of wornout carbon brushes , slip rings , etc. alongwith its other associated gears & as such a

motor having wound rotor has not become much popular in the world.

Squirrel cage motors are having a slight draw back because these motors take higher Starting

current from the MAINS at the time of starting. Direct On Line is the simplest starting procedure

& in this method high starting torque is associated with very high starting currentand as such theSupply Authorities in different countries / states have formulated various regulations to limit the

Starting- current of these Squirrel cage induction motors. In some countries / states, the Starting

current of these motors is brought to a considerable limit by incorporating a Star Delta starter.

The Star Delta method of motor starting gives a fixed starting torque, as the applied voltage in

Star is a fixed ratio of its line voltage. By Star Delta starting the starting current and starting

torque will reduce to 33% of the direct on line values. Furthermore, because of considerable

Current Transients produced by the Open Switching process ( when changing over from Star to

Delta connections ) the Star Delta method of starting the large Squirrel cage motors is not

considered to be a safer method ( ISS : 3914 - 7.1.6 ).

As per code of practice for selection of ac induction motor starters (voltage not exceeding 1000volts ) in different countries / states -The Star Delta starting may only be employed for such

drives which permit bringing up the motor, even when connected in Star ( start ) , almost close (

about 90 percent ) to the full speed.

An earlier changeover from Star ( start ) to Delta ( run ) may lead to heavy inrush currents & not

too smooth a starting.

In case ofWauchope closed transition star delta starter,one can not vary the starting torque,

though it is a closed transition type star delta starter. In case of drives where starting torque

required by the machine is more than what is developed by the motor, there would be heavy

current-transients while changing from star to delta connections, as the applied voltage in Star is

fixed.

While considering the Primary Resistor Starters this method consists of connecting the motor to the

line through a series resistor in each phase. The main disadvantage of this type of starter is that for

the same starting torque, the line current & thus power taken from the MAINS is much higheras

compared with the star delta or an autotransformer starter.

The other method of reduced voltage starting is an Auto Transformer Starter (conventional). This

starter gives reduced voltage to the motor by means of an auto-transformer in the motor circuit at

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the time of starting ; after a definite time interval and after the motor accelerates, it is transferred

from the reduced voltage to the full voltage.

The auto-transformers are generally provided with voltage taps. It is possible to vary the starting

current and torque within the limits of the tappings provided. UNLESS CLOSED TRANSITION

KORNDORFER METHOD IS ADOPTED THIS STARTER HAS THE SAME DISADVANTAGE OF OPENING

THE CIRCUIT BEFORE THE MOTOR IS CONNECTED TO THE LINE AND PRODUCING SIMILAR

TRANSIENT CURRENT AND STRESSES.

FROM THE ABOVE EXPLANATIONS ONE MAY CONCLUDE THAT THE BEST ELECTRICAL METHOD

OF STARTING A SQUIRREL CAGE INDUCTION MOTOR IS A FULLY AUTOMATIC AUTO-

TRANSFORMER STARTER WITH KORNDORFER CLOSED TRANSTION PRINCIPLE.

HERE WE MAY MENTION THAT WE ARE GLAD THAT WE HAD DEVELOPED THE SAME

IN THE NAME - AUTO - STRESTER

THE MAJOR ADVANTAGE OF THE AUTO - STRESTER IS THAT IN MOST OF THE CASES IT REPLACES THE INSTALLATION OF

SLIP-RING MOTOR WITH SQUIRREL CAGE MOTOR.

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Direct OnLine StarterAdvantages It is the cheapest starter available

It provides 100% torque at the time of starting

Motor is connected in delta at motor terminals

Only one set of cable is required from starter to motor

Disadvantages

It draws 6 times current of the Full load ampere at the time ofstarting resulting in possible burnout of motor and / or starter.

There is a big voltage dip in the electrical installation because of

high in-rush current and therefore not suitable for higher size

squirrel cage motors.

Significant energy wastage and reduced motor life.

Star Delta Starter

Advantage It draws 2 times starting current of the full load ampere of the

motor connected

It is an open transition principle method while changing from star

to delta connections

Disadvantage It provides only 33% starting torque and if the load connected tothe subject motor requires higher starting torque at the time of

starting than very heavy transients and stresses are produced while

changing from star to delta connections, and because of these

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transients and stresses many electrical and mechanical break-down

occurs In this method of starting initially motor is connected in star and

than after change over the motor is connected in delta. The delta of

motor is formed in starter and not on motor terminals

It requires 2 set of cables from starter to motor

ATS (Conventional)

Advantages It draws less current from the mains and simultaneously delivers

more current to the motor

It can limit the starting current to any desired value

One can vary the starting torque of the motor as per the tappings

provided

Only one set of cable is required from starter to motor


Disadvantages It is an open transition principle method while changing from ATS to

delta connections

Heavy transients and stresses are produced while changing from

ATS to delta connections because of open transition principle and

these results in electrical break-down

It is costlier than Star Delta Starter

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THE AUTO-STRESTERFully Automatic Autotransformer Starter with

Korndorfer Closed Transition Principle with

Primary Off Logic

Advantages It draws less current from the mains and

simultaneously delivers more current to the

motor

It can limit the starting current to any desired

value

One can vary the starting torque of the motoras per the tappings provided very conveniently

It is a Korndorfer closed transition principle

method while changing from ATS to delta

connections

Practically no transients and stresses are

produced while changing from ATS to deltaconnections and thus increases the electrical

and mechanical life of the installation

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Only one set of cable is required from starter

to motor


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ATS_Writeup.81183803