Download ppt - MakeItOrTakeIt

SINGLE PHASE INDUCTION
MOTOR SOFT START BY STEPPED
DELAY OF REDUCING FIRING
ANGLE
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Contents
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Project overview
Block diagram
Power supply
Induction Motor
Soft start of IM
Comparator
Opto-isolator
Schematic & Working of the project
Advantages
Applications
Future scope
Conclusion
Project overview
• These Solid State Switches are phase
controlled in a similar manner to a light
dimmer, in that they are turned on for a part
of each cycle.
• The average voltage is controlled by varying
the conduction angle of the switches.
• Increasing the conduction angle will increase
the average output voltage.
• Controlling the average output voltage by
means of solid state switches has a number
of advantages.
Contd..
• One of the major advantages being the
vast improvement in efficiency relative to
the primary resistance starter, due to its
low on state voltage of the solid state
switches.
Block diagram
Power supply
Contd..
• The 230V AC supply is first stepped down
to 12V AC using a step down transformer.
• This is then converted to DC using bridge
rectifier.
• The AC ripples is filtered out by using a
capacitor and given to the input pin of
voltage regulator 7812.
• At output pin of this regulator we get a
constant 12V DC which is used for
different ICs in this project.
Induction Motor
• The single-phase induction machine is the most frequently
used motor for refrigerators, washing machines, clocks,
drills, compressors, pumps, and so forth.
• The single-phase motor stator has a laminated iron core
with two windings arranged perpendicularly.
• One is the main and
• The other is the auxiliary winding or starting winding
Contd..
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This “single-phase”
motors are truly twophase machines.
The motor uses a
squirrel cage rotor,
which has a laminated
iron core with slots.
Aluminum bars are
molded on the slots
and short-circuited at
both ends with a ring.
Stator with laminated
iron core
Main winding
Slots with winding
Rotor with
laminated
iron core
+
+
Bars
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Starting winding
Ring to short
circuit the bars
Soft starter
• A soft starter is another form of reduced voltage starter
for A.C. induction motors.
• The soft starter is similar to a primary resistance or
primary reactance starter in that it is in series with the
supply to the motor.
• The current into the starter equals the current out.
• The soft starter employs solid state devices to control
the current flow and therefore the voltage applied to
the motor.
• Soft starters are connected in series with the line
voltage applied to the motor, or can be connected
inside the delta loop of a delta connected motor,
controlling the voltage applied to each winding.
Contd..
• Voltage control is achieved by means of
solid state A.C. switches in series with one
or more phases. These switches comprise
either:
a. Triac
b. diode & SCR
c. Two SCRs
SCR
• A Silicon Controlled Rectifier (or Semiconductor
Controlled Rectifier) is a four layer solid state
device that controls current flow
• An SCR can be seen as a conventional rectifier
controlled by a gate signal
• It is a 4-layered 3-terminal device
• When the gate to cathode voltage exceeds a
certain threshold, the device turns 'on' and
conducts current
Contd..
• The operation of a SCR can be understood in
terms of a pair of tightly coupled Bipolar Junction
Transistors
• SCR has three states:
• Reverse blocking mode, forward blocking mode,
and forward conducting mode
Comparator
• op amps & comparators look very similar
• But a comparator gives a logic output
indicating the relative potentials on its two
inputs
• An op amp amplifies the differential
voltage between its two inputs – and is
designed always to be used in closed-loop
applications
Contd..
• Potential dividers are connected to the
inverting and non inverting inputs of the opamp to give some voltage at these
terminals.
• Supply voltage is given to +V and –V is
connected to ground.
• The output of this comparator will be logic
high (i.e., supply voltage) if the noninverting terminal input is greater than the
inverting terminal input of the comparator.
• If the inverting terminal input is greater than
the non-inverting terminal input then the
output of the comparator will be logic low
(i.e., gnd).
Optocoupler
• Opto coupler is a 6 pin IC. It is a combination of
1 LED and a diac. Pin 5 is not generally used
and when light falls on the diac then it switches
ON the diac.
Contd..
• When logic zero is given as input to the LED then
the light doesn’t fall on diac so the diac is off
means the current does not flow through the diac.
• When logic 1 is given as input to the LED then
light emitted by LED falls on diac so it starts
conducting i.e., now there will be current flowing
through the diac.
Working of project
• To start the motor with low current, two
SCR’S are connected back to base in each
phase.
• They are triggered slowly initially and
gradually the triggering pulse is increased, so
that motor gets high current after a time delay
when windings are in the position of
withstanding the high current.
• To trigger the gates of SCRS the op-amps
are used.
• Op-amp is configured to get a level voltage
that will initially be high and gradually fall to
zero.