Starting Methods of IM

8/12/2019 Starting Methods of IM

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M R S . C H A M I L A S U M A T H I R A T N A - F I V T


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MAIN STARTING METHODS

Across the line starting

Next Slide

Reduced voltage starting

Slide 9


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ACROSS THE LINE STARTING

full voltage start

simplest method of starting

Capable of

drawing full in-rush currentand

developing maximumstarting torque to acceleratethe load to speed in theshortest

possible time.


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ACROSS THE LINE STARTING(DIRECT ON LINE)

Manual Motor StartersNext Slide

Magnetic Motor StartersSlide 7


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MANUAL MOTOR STARTERS

The main advantage of a manual motor starter is lower cost

often used for smaller motors

Since the switch contacts remain closed if power is removed from the circuit

without operating the switch, the motor restarts when power is reapplied

which can be a safety concern.

remote control or auxiliary control equipment like a magnetic starter cannot

be used.


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MANUAL STARTER


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MAGNETIC MOTOR STARTERS

A magnetic motor starter is a packageconsisting of a contactor and overload

protection

Magnetic starters are used with larger

motors (required above 10

horsepower) or where greater motor

control is desired.

The main element of the magnetic

motor starter is the contactor


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MAGNETIC MOTOR STARTERS

slide 2


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PROBLEMS INCORPORATED IN DOL STARTING

Large drop in the supply system

voltage,


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REDUCED VOLTAGE STARTING

connects the motor windings/terminalsat lower than normal line voltage

used when the current in-rush formthe motor starting adversely affects

the electrical system. needed to reduce the mechanical jerk

reduces the current in-rush to the

motor and also reduces the startingtorque


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If the driven load or the powerdistribution system cannot accept a full

voltage start, some type of reducedvoltage or "soft" starting scheme mustbe used.


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TYPICAL REDUCED VOLTAGE STARTER TYPES

Star-Delta Starters Slide 13

Autotransformer Starters Auto transformer starter

Resistance Starters

Frequency Converters

Soft Starters

Reduced voltage starters can only beused where low starting torque is

acceptable


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STAR DELTA STARTER

This is the simplestand most widely used

method of starting

Initially connects as

star and then as delta.This reduces voltage

by 58%

The main advantage is

simplicity

Show how the starting

current is reduced whenconnected in star than

connected in delta


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POWER CIRCUIT OF STAR DELTA METHOD

Typical reduced voltage starter types


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AUTO TRANSFORMER STARTER

Each phase of an auto transformer consists of a single winding on a

laminated core.

The motor is first connected to the reduced voltage output, and when

the current has fallen to the running value, the motor leads are switchedover to the full voltage.

switchover from the starting tap to the full voltage inevitably results in

mechanical and electrical shocks to the motor


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RESISTANCE STARTERS

inserting three resistors or inductors of

appropriate value in series

with the motor

When the motor is up to speed, theadded impedance is shorted-out by

means of a contactor

used with small motors where asmooth jerk free start is required, for

example textile lines.


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FREQUENCY CONVERTER(VFD/VSD)


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SOFT STARTERS

It has thyristors in the main circuit, and the

motor voltage is regulated motor voltage islow

during start, the starting current and startingtorque is also low. One of the benefits with

this starting method is the possibility to adjustthe torque to the exact need

Another feature of the soft starter is the softstop function


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SOFT STARTER


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COMPARISON OF REDUCED VOLTAGE STARTING

METHODS


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SOFT STARTER TORQUE AND CURRENT VS SPEED


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COMMON SETTINGS

The setting can be done either by adjusting potentiometers, changing dip

switches, using a key pad, a computer or similar.

Start ramp

Stop ramp

Initial Voltage


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The only real drawback over

conventional starters is that the mains

currents during run-up are not

sinusoidal

valuable where the load must not be

subjected to sudden jerks

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Starting Methods of IM