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EXPERIMENT : AUTO TRANSFORMER STARTER
1. AIM
To provide knowledge in Auto Transformer Starter
2. OBJECTIVES
To familiarize the student with:
1.1 Control circuit and main circuit for Auto Transformer Starter
1.2 Operation in starting AC motor with Auto Transformer Starter.
1.3 Control equipment for Electrical Motor Control
3. EQUIPMENT
Bil
1. 3 phase Contactor 3 unit
2. Thermal Overload Relay (TOR) 1 unit
3. Push button Start 1 unit
4. Push button Stop 1 unit
5. Miniature Circuit Breaker (MCB) 1 unit6. Molded Case Circuit Breaker (MCCB) 1 unit
7. Pilot lamp 2 unit
8. 3 phase AC motor (3/4 ~ 3 hp) 1 unit
9. Timer (TDR) 1 unit
10. Relay 1 unit
11. Cable Necessary
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4. THEORY
Auto transformer starter
This starter produces highefficiency and have the option to be adjusted to obtain the
necessary torque and in accordance with the system. It veryefficiency starter but the
disadvantage is it very high cost to setup control panel starter.
It can improved torque ratio is achieved and starting current is typically 3 times Full Load
Current , depending on the voltage taps selected. Typically it have taps at 50%,65% and
80% voltage.
During start-up, the motor is connected to theauto transformers tapping. This means that
the motor starts up with a reduced voltage and a correspondingly low current.
What is auto transformer starter?
Theauto transformer reduces the current in the mains supply line further and in
accordance with its ratio. The technique for connecting an AutoTransformer starter is via
magnetic contactor and connect the motor to taps by mean of the contactor.
When motor accelerate to full speed, the tap of contactor was open and disconnecting
motor fromtransformer and other contactor close to connecting the motor to the supply.
When the motor has almost reached its rated torque, the starconnection on the
transformer is opened.
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ADVANTAGES OF AUTO TRANSFORMER STARTER:
a ) On the 65% tapping the line current is approximately equal tp that of a Star-Delta
starter, however, at the time of switching from reduced voltage to the full supply voltage,
the motor is not disconnected so that the second peak is very much reduced since the
transformer is converted into reactance for a short time
b ) It is possible to vary the tapping from 65% to 80% or even up to 90% of the supply
voltage in order to ensure that the motor starts satisfactorily.
DISADVANTAGES OF AUTO TRANSFORMER STARTER:
a ) One of its great disadvantages is the limitation of its operation frequency. It is always
necessary to know the operation frequency in order to determine a suitably rated auto-
transformer.
b ) The compensating switch is much more expensive than a Star-Delta starter due to the
auto-transformer.
c ) Due to the size of the auto-transformer starter, much larger control panels are required
which increases the price.
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5. EXPERIMENT PROCEDURE
5.1 EXERCISE 1 : CONTROL CIRCUIT
5.1.1 Will make a connection to the control circuit as shown in Figure 1 (a) or
1 (b)
5.1.2 Taking incoming voltage from 1 to 3 lines (R or Y or B) on a single
phase.
5.1.3 After that I'll connect circuit line is back to neutral (N) using a black
cable.
5.1.4 Experiments will be done on this circuit by making the circuit
connections to the power supply control circuit for testing purposes.
5.1.5 Please refer to the operation of the circuit is
Figure 1(a): control circuit of Auto Transformer Starter
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5.2 EXERCISE 2 : MAIN CIRCUIT
5.2.1 Main circuit connections as shown in Figure 2.
5.2.2 Supply coming to this track is from the 3 phase 415V (R, Y, B, and N)
5.2.3 I will make a connection from the earth (E) to the 3-phase motor.
5.2.4 Then I will make a series of experiments on the circuit is armed with 3-
phase supply is to make full operation on the main circuit and control
circuit AC Motor
5.2.5 Please refer to this operation Auto Transformer Starter
Figure 2: Main circuit of Auto Transformer Starter
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6. DISCUSSION
6.1 Briefly explain the result of this experiment
After the supply was connected to the motor control circuit , press the start
button is pressed will start , after which the current flows through the coil C4
and will get current supply circuit and the contacts N / O C4 will turn into N /
C and timer coil will get electricity . Three main contact S4 will be closed ( N
/ C ) and will be connected to a timer and supply will be doubled. Timer
contacts N / O will turn into a camera and timer coil will get electricity , touch
timer increased N / C will open . With this auto transformer is connected in a
star shape . And voltage to the motor . In addition, the contact is closed N / C
contacts will switch to open N / O to N / C . Therefore , C3 supply and thus
completing the circuit and the motor will rotate .
6.2 Briefly explain the operation of Auto transformer starter.
When the start button is pressed, coils CR, TR, SC1, and SC2 energize.
When the SC1 and SC2 load contacts close, the motor is connected to the
center tap of the open delta auto transformer. Since the transformers have beencenter tapped, the motor is connected to half of the line voltage. A basic
schematic diagram of this connection is shown in Ill. 2.
The normally closed SC1 and SC2 auxiliary contacts connected in
series with the R coil open to provide interlock and prevent the R contactor
from energizing as long as SC1 or SC2 is energized.
After some time, TR timer reaches the end of its timing sequence and
the two timed TR contacts change position. The normally closed TR contact
connected in series with coils SC1 and SC2 opens and de-energizes these
contactors. This causes all SC1 and SC2 load contacts to open and disconnect
the autotransformer from the line. The normally closed SC1 and SC2 auxiliary
contacts connected in series with R coil reclose.
When the normally open TR contact connected in series with R coil
closes, the R contactor energizes and closes all R load contacts. This connectsthe motor directly to the power line.
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The normally closed R auxiliary contact connected in series with coils
SC1 and SC2 opens to provide interlock. The motor will continue to run until
the stop button is pressed or an overload occurs
6.3 Expline function of equipment list.
3 phase Contactor
The top three contacts switch the respective phases of the incoming 3-
phase AC power, typically at least 480 Volts for motors 1 horsepower or
greater. The lowest contact is an "auxiliary" contact which has a current rating
much lower than that of the large motor power contacts, but is actuated by the
same armature as the power contacts. The auxiliary contact is often used in a
relay logic circuit, or for some other part of the motor control scheme,
typically switching 120 Volt AC power instead of the motor voltage. One
contactor may have several auxiliary contacts, either normally-open or
normally-closed, if required.
Thermal Overload Relay (TOR)
Thermal overload relays are 3 pole. The motor current flows through
their bimetals (1 per phase) which are indirectly heated.Under the effect of
the heating, the bimetals bend, cause the relay to trip and the position of the
auxiliary contacts to change.The relay setting range is graduated in amps. In
compliance withinternational and national standards, the setting current is the
motor nominal current and not the tripping current (no tripping at 1.05 x
setting current, tripping at 1.2 x setting current). The tripping curves (cold or
warm starting, 3 phases and 2 phases) are shown in the main catalog. The
relays are built to be self protecting in theevent of an overload until the short
circuit protection device is activated
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Push button Start
Contains a pair of existing open contacts (normally open, NO) which
willclosed when the Button is pressed. When ready to open contacts closed,
current will flowing in the circuit.
Push button Stop
Contains a pair of normally closed contacts (normally closed, NC),
which will be open when Button is pressed. When ready to close the contacts
open, it will be decided the flow of electric current.
Miniature Circuit Breaker (MCB)
Miniature circuit breakers or MCBs are used to replace fuses that
protect individual pieces of electrical equipment and the circuits which supply
them with power
Molded Case Circuit Breaker (MCCB)
Molded case circuit breakers are designed to provide circuit protection
for low voltage distribution systems. They protect connected devices against
overloads and/or short circuits
Pilot lamp
A pilot lamp is a light that illuminates under specific conditions, most
commonly when an electrical circuit is energized. It may also be known as an
indicator lamp or pilot light, although this should not be confused with a small
flame kept burning in a gas appliance to provide a source for ignition when the
appliance is turned on. Pilot lamps are used in a wide variety of settings and in
some cases are required by law for safety reasons
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3 phase AC motor (3/4 ~ 3 hp)
Induction motor or asynchronous motor is a type of AC motor where
power is supplied to the rotor by electromagnetic induction. Electric motor for
rotating the magnetic force applied between a stationary electromagnet called
the stator with a rotating elektrimagnet called the rotor.
Timer (TDR)
The TDR series of electronic relays is a processor based control thatcan have many different functions. The operation of the TDR is determined at
the time of manufacture, based on the firmware loaded into the relay.
Special functions (X) that are unique to a customers specific application are
available by contacting the factory.
Relay
A relayis anelectrically operatedswitch. Many relays use
anelectromagnet to mechanically operate a switch, but other operating
principles are also used, such assolid-state relays.Relays are used where it is
necessary to control a circuit by a low-power signal (with complete electrical
isolation between control and controlled circuits), or where several circuits
must be controlled by one signal. The first relays were used in long
distancetelegraph circuits as amplifiers: they repeated the signal coming in
from one circuit and re-transmitted it on another circuit. Relays were used
extensively in telephone exchanges and early computers to perform logical
operations.
A type of relay that can handle the high power required to directly
control an electric motor or other loads is called acontactor.Solid-state
relays control power circuits with nomoving parts, instead using a
semiconductor device to perform switching. Relays with calibrated operating
http://en.wikipedia.org/wiki/Electrichttp://en.wikipedia.org/wiki/Switchhttp://en.wikipedia.org/wiki/Electromagnethttp://en.wikipedia.org/wiki/Solid-state_relayhttp://en.wikipedia.org/wiki/Electrical_telegraphhttp://en.wikipedia.org/wiki/Contactorhttp://en.wikipedia.org/wiki/Solid-state_relayhttp://en.wikipedia.org/wiki/Solid-state_relayhttp://en.wikipedia.org/wiki/Moving_partshttp://en.wikipedia.org/wiki/Moving_partshttp://en.wikipedia.org/wiki/Solid-state_relayhttp://en.wikipedia.org/wiki/Solid-state_relayhttp://en.wikipedia.org/wiki/Contactorhttp://en.wikipedia.org/wiki/Electrical_telegraphhttp://en.wikipedia.org/wiki/Solid-state_relayhttp://en.wikipedia.org/wiki/Electromagnethttp://en.wikipedia.org/wiki/Switchhttp://en.wikipedia.org/wiki/Electric -
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characteristics and sometimes multiple operating coils are used to protect
electrical circuits from overload or fault, in modern electric power systems
these functions are performed by digital instruments still called "protective
relays".
Cable
Cable has a function that acts as a media transimisi to accelerate the
delivery of the message
6.4 What the advantages and disadvantages of this starter compared to the other
type of starter (Dierect On Line Starter, Star-Delta Starter, ETC)
ADVANTAGES OF AUTO TRANSFORMER STARTER:
On the 65% tapping the line current is approximately equal tp that of a
Star-Delta starter, however, at the time of switching from reduced
voltage to the full supply voltage, the motor is not disconnected so that
the second peak is very much reduced since the transformer is
converted into reactance for a short time
It is possible to vary the tapping from 65% to 80% or even up to 90%
of the supply voltage in order to ensure that the motor starts
satisfactorily.
DISADVANTAGES OF AUTO TRANSFORMER STARTER:
One of its great disadvantages is the limitation of its operation
frequency. It is always necessary to know the operation frequency in
order to determine a suitably rated auto-transformer.
The compensating switch is much more expensive than a Star-Delta
starter due to the auto-transformer.
Due to the size of the auto-transformer starter, much larger control
panels are required which increases the price.
http://en.wikipedia.org/wiki/Protective_relayhttp://en.wikipedia.org/wiki/Protective_relayhttp://en.wikipedia.org/wiki/Protective_relayhttp://en.wikipedia.org/wiki/Protective_relay -
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ADVANTAGES OF DOL STARTER
Most Economical and Cheapest Starter
Simple to establish, operate and maintain
Simple Control Circuitry
Easy to understand and troubleshoot.
It provides 100% torque at the time of starting.
Only one set of cable is required from starter to motor.
Motor is connected in delta at motor terminals.
DISADVANTAGES OF DOL STARTER
It does not reduce the starting current of the motor.
High Starting Current: Very High Starting Current (Typically 6 to 8
times the FLC of the motor).
Mechanically Harsh: Thermal Stress on the motor, thereby reducing its
life.
Voltage Dip: There is a big voltage dip in the electrical installation
because of high in-rush current affecting other customers connected to
the same lines and therefore not suitable for higher size squirrel cage
motors
High starting Torque: Unnecessary high starting torque, even when not
required by the load, thereby increased mechanical stress on the
mechanical systems such as rotor shaft, bearings, gearbox, coupling,
chain drive, connected equipments, etc. leading to premature failure
and plant downtimes.
ADVANTAGES OF STAR DELTA STARTER:
a ) Star-Delta starters are widely used due to their relatively low price.
b ) There are no limits to the number of times they can be operated.
c ) The components require very little space.
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d ) The starting current is reduced to approximately one-third.
DISADVANTAGES OF STAR DELTA STARTER:
a ) The starter can only be applied to motors where the six leads or terminals
can be accessed.
b ) The supply voltage must be the same as the rated motor voltage for Delta
connection.
c ) Because the starting current is reduced to approximately one-third of the
rated current, the starting torque is also reduced to one-third.
d ) If the motor does not reach at least 90% of its rated speed at the time of
switching from Star to Delta the current peak will be as high as in a D.O.L.
start, thus causing harmful effects to the contacts of the contactors and the
connection system brings no advantage to the electrical system.
The advantages/disadvantages of different types of motor starters like
DOL, star/ delta, korndorfer, primary resistance/reactance, shunt capacitance,
slip ring, vfd, vsd, auto transformer etc.
DOL (simple start up but reflect to high voltage drop, high starting
current, low starting period duration)less power saving. star/delta decrease the
starting current to 1/3 but required many relays for control change between
start connection then to delta.
Auto transformer used for MV application by connect less voltage on
motor during start up then change to nominal voltage on motor terminals after
start up where reflect to decrease the starting current and decrease the voltage
drop but increase the starting duration (very expensive where required 3
MVCB one for motor and one for primary of auto and one for secondary of
auto).
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VSD or VFD used for application where its worked with inlet guide
van or valve (variable load) to make power saving. Capacitor used to avoid the
voltage drop during motor start up but may cause many problems like
resonance.
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CONCLUSION
The end of the experiment on the autotransformer starter, I can learn about the controlcircuit and main circuit for Auto Transformer Starter. With that I also can find more detail
about the operation to start the AC motor with Auto Transformer Starter. And I can also learn
about the tools used to Electric Motor Control. Other than that, I can also see myself
operations performed in the circuit autotransformer starter. With that I also can learn how
Connection to a fully autotransformer circuit.
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Reference
1. http://iitg.vlab.co.in/?sub=61&brch=168&sim=941&cnt=1
2. http://en.wikipedia.org/wiki/Relay
3. http://www.industrial-electronics.com/lab_manual_electr_41.html
4. http://top10electrical.blogspot.com/2014/03/advantages-and-disadvantages-of-
auto.html
5. http://www.softstarter.org/advantages-disadvantages-of-different-motor-starters-
526301.html
6.
http://iitg.vlab.co.in/?sub=61&brch=168&sim=941&cnt=1http://iitg.vlab.co.in/?sub=61&brch=168&sim=941&cnt=1http://en.wikipedia.org/wiki/Relayhttp://en.wikipedia.org/wiki/Relayhttp://www.industrial-electronics.com/lab_manual_electr_41.htmlhttp://www.industrial-electronics.com/lab_manual_electr_41.htmlhttp://top10electrical.blogspot.com/2014/03/advantages-and-disadvantages-of-auto.htmlhttp://top10electrical.blogspot.com/2014/03/advantages-and-disadvantages-of-auto.htmlhttp://top10electrical.blogspot.com/2014/03/advantages-and-disadvantages-of-auto.htmlhttp://top10electrical.blogspot.com/2014/03/advantages-and-disadvantages-of-auto.htmlhttp://top10electrical.blogspot.com/2014/03/advantages-and-disadvantages-of-auto.htmlhttp://www.softstarter.org/advantages-disadvantages-of-different-motor-starters-526301.htmlhttp://www.softstarter.org/advantages-disadvantages-of-different-motor-starters-526301.htmlhttp://www.softstarter.org/advantages-disadvantages-of-different-motor-starters-526301.htmlhttp://www.softstarter.org/advantages-disadvantages-of-different-motor-starters-526301.htmlhttp://www.softstarter.org/advantages-disadvantages-of-different-motor-starters-526301.htmlhttp://www.softstarter.org/advantages-disadvantages-of-different-motor-starters-526301.htmlhttp://www.softstarter.org/advantages-disadvantages-of-different-motor-starters-526301.htmlhttp://top10electrical.blogspot.com/2014/03/advantages-and-disadvantages-of-auto.htmlhttp://top10electrical.blogspot.com/2014/03/advantages-and-disadvantages-of-auto.htmlhttp://www.industrial-electronics.com/lab_manual_electr_41.htmlhttp://en.wikipedia.org/wiki/Relayhttp://iitg.vlab.co.in/?sub=61&brch=168&sim=941&cnt=1 -
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Before testing
Time test,blue lamp is ON
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Trip lamp