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As we know, once a supply is connected to a
three phase induction motor a rotating
magneticfield will be set up in the stator, this
will link and cut the rotor bars which in turn will
induce rotorcurrents and create a rotor field
which will interact with the stator field and produce rotation. Ofcourse this means that the
three phase induction motor is entirely capable
of self-starting.The need for a starter therefore is
not, conversely enough, to provide starting but
to reduceheavy starting currents and provide
overload and no-voltage protection.There are a
number of different types of starter including
The Direct On-line Starter, The Star- Delta
Starter, Auto-Transformer and Rotor
resistance.
IV. Direct-on-LineDirect-on-line (DOL) is the simplest form motor
starting method had being used. It is a traditionally
started and stopped by applying and removing the
supply from the circuit. During starting, the full
voltage are acceptable to used, but to avoid large
starting current from occur, the voltage starter need to
be reduced. The DOL starter comprises a switch and
an overload protection relay as shown in figure1.
Figure 1.Direct-On-Line motor starter.
The switch may be manual or automatically depends
on the user. In previous, manually operated load
break switch are used, but more commonly an
electromagnetic contactor are used which can be
opened by thermal overload relay. Contactors
arecontrol by separated star and stop button and
auxiliary contact used to hold the supply when the
start button is release. By applying full line voltage to
the motor winding during motor starting, it will draw
a very high inrush current up to 6 to 7 times rated
motor current and sometimes it may increase up to 9
to 10 times the rated current exist. Using this starting
method, will produce a very high starting torque and
usually higher than required for most application.For
a very short time, to establish the magnetic field in
the iron. This inrush current are valued in between
V. Star-DeltaStar-delta motor starting method are also known as
soft starting method. Star-delta starting is when the
motor in connected in STAR connection during
starting sequence. The motor then connected to
DELTA when it accelerated to close to the normal
running speed. In order to allow the motor to start,
the motor windings are configured in a star formation
to the supply voltage. The voltage is supply to the
individual motor windings therefore it reduced by a
factor of this connection amounts to
approximately 30% of the delta values. By using this,
it reduced to one third of the direct starting current
(DOL). Due to the reduction of starting torque, the
star-delta connection is suitable for drives with high
inertia mass but a resistance torque which is low or
only increased speed. After motor run-up, in most
cases an automatic timing relay controls the switch-over from star to delta. The run-up using star
connection should last until the motor reach the
operational value. During the switching from star to
delta, the will be an occurrence of high current as
seen with direct-on-line starting. During delta
connection, the full mains voltage is applied to the
motor windings. To enable a switch-over from star to
delta, the six ends of the motor winding are
connected onto terminals. Figure 2 shows the star-
delta motor starting wiring.
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Figure 2: Star-delta motor starting wiring
This method can only be used if when the starting
works is light loaded. If the motor start in heavily
loaded there will not be enough torque to accelerate
the motor up to speed required.
VI. AutotransformerAn autotransformer starter uses an auto transformer
to reduce the voltage applied to a motor during start.
By having a number of output taps such as 50%, 65%
and 80% to be set-up to provide a single stage starter
or a multistage starter enable the motor to be started
at one or more of these settings. There are two ways
of connecting an autotransformer starter, first, by
applying full voltage to the transformer via a
contactor and connect the motor to the tap by means
of the contactor. The tap contactors will opens or
disconnecting the motor from the transformer and
another contactor closes connecting the motor to the
supply when the motor has accelerated to full speed
or has run out of acceleration torque. This is known
as an open transition starter and it is less than ideal
due to the fact that the motor is disconnect for a short
period of time during the start period. While the
motor is connected and accelerating, it also acts as a
generator until the rotor field decays. The voltage
generated by the motor is not synchronized to the
supply, and so on reconnection to the supply, the
voltage across the contactor at closure can be as
much as twice the supply voltage resulting in a veryhigh current and torque transient. The transition
switching or known as auto-reclose effect as it yields
similar characteristic to opening and closing a
breaker on a supply to the motor. By using
autotransformer motor starting method, it can reduce
the torque as the square of the applied voltage. Figure
3 shows the autotransformer motor starting wiring.
Figure 3. Autotransformer motor starting wiring
VII. Result & Discussion
In this paper the power quality event that occur in
the system due to the different motor starting are
review by using the PSCAD (Power System CAD)
software.There are three type of motor starting are
being consider in this paper which is Direct-On-
Line(DOL), Star-Delta and Autotransformer.
During DOL motor starting, the motor are connected
direct to the load and having a breaker function as a
switch and a transformer used to isolate the motor
circuit from the power supply as shown in figure 4
below. The motor torque are fixed to 5NM and speed
of motor van be varied from 0 to 10 rad/s.
Figure4. Direct-On-Line motor starting circuit
From figure 4, loads are connected in parallel to the
motor. A volt meter and ammeter are connected to
the load and when motor starting it results voltage
sag to the loads. During motor starting, the inrush
current occurs in the induction motor starting and it
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causes the voltage and current terminal to drop in
magnitude. Graph 1 and 2 shows the voltage and
current output at load.
Graph1. Voltage Sag occur in DOL motor starting
Graph2. Current Sag occur in DOL motor starting
In star-delta motor starting connection, the same load,
motor and transformer are used from DOL motor
starting connection as shown in figure 5. The
difference is that, these circuits are using two breaker
functions as switch to change connection from star
supply for motor starting and to delta supply when
the motor reach the operation speed.
Figure 5.Star-Delta motor starting circuit
Once again a volt meter and ammeter are connected
to the load connection to measure the voltage and
current flow through load. As shown in graph 3 and
4, the voltage and current sag are still occur but this
time it less than the DOL voltage and current sag.
Graph 3 and 4 also shows that waveform drop for a
moment and then back to the normal when the motor
already reach the operational speed.
Graph 3.Voltage sag occur in star-delta motor starting
Graph 4. Current sag occur in star-delta motor starting
Same as star-delta starting connection, this circuit
still using same motor, transformer, breaker and load.But this time, three autotransformer are added to the
circuit function as a supply to the motor as shown in
6.
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Figure 6.Autotransformer motor starting circuit
As shown in graph 5 and 6, the voltage and currentsag still occur at the load but this time drop value are
less compare with the other two starting method.
Graph 5. Voltage sag occur in autotransformer motor starting
Graph 5.Current sag occur in autotransformer motor starting
VIII. ConclusionElectrical power quality which is one of the topics for
several power utilities all over the world, and its
becoming an important and challenging issue for the
power engineers. There is no unique model can be
used to assess the power quality problem and to
identify and classify them properly.
By using PSCAD software to create power quality
event (voltage sag) due to different motor starting
method, shows that out of three methods, the star-delta method are the one that only method that
produce small amount of voltage and current sags
and at the same time it repair back the signal compare
with the other two method.
In order to repair or solve back this problem, a few
solutions have being suggested due to problem
occurred. By installing an Uninterruptable Power
Supply (UPS) will help the system to maintain the
supply when there is any disturbances occur in the
system. There is several types of UPS are available
depending on the problem such as Standby UPS,
Online UPS, and Hybrid UPS. Each UPS has its own
advantage and disadvantage but Standby UPS are
commonly used out of the other two types of UPS.
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