starting methods of im
TRANSCRIPT
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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