03-05-2013, 03:02 PM
Solid State Starter with Single Phasing preventer for Three Phase Induction Motor
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Abstract:
In this paper, advantage of soft starter is shown. A
IC555 based soft starter with its usefulness is shown. A cheapest
and reliable single phasing preventer which is working on open
delta principle is explained. And at last implementation of
combine Soft starter with single phasing preventer is shown. A
comparison of different types of starters is also shown.
Index Terms Silicone rubber, FRP, HTV, Weather shed, finite
element method, Electric field distribution, potential distribution,
clean condition, contamination condition.
INTRODUCTION
The disadvantage with Direct on line starting method is that
it gives the highest possible starting current. A normal value is
between 6 to 7 times the rated motor current but values of up
to 9 or 10 times the rated current exist. Besides the starting
current there also exists a current peak that can rise up to 14
times the rated current since the motor is not energized from
the first moment when starting. The values are dependent on
the design and size of the motor, but in general, a smaller
motor gives higher values than a larger one. During a directon-
line start, the starting torque is also very high, and is higher
than necessary for most applications. The torque is the same as
the Force and an unnecessary high force give Unnecessary
high stresses on couplings and the driven application.
Naturally, there are cases where this starting method works
perfectly and in some cases also the only starting method that
works. Solid state starter will be very useful as compared to
direct on line starting or other starters.
Block diagram of solid state starter with
preventer
In above circuit we can show the overall block diagram of
“Solid State Starter and Single Phasing Preventer”. DC supply
is required for solid state starter. It is provided from main ac
supply, which converts in dc by using rectifier circuit. Solid
state starter gives a signal to relay and relay make the n/o or
n/c contact with appropriate relay logic contactor will operate
and motor connection connect in star or delta as per contactor
operation.
SOLID STATE STARTER
This circuit is one such starter. It is a very low-cost but
highly reliable gadget; besides being fool-proof. The
circuit basically consists of a 555 timer chip (ICI). This
timer switches on the 100 ohm, 12V relay (connected in
star mode for starting and delta mode for running by using
of 2 no of contactor ,C-3 contactor connect motor
connection in star and C-2 is connect in delta ) after a
delay of about 60 seconds approximately, hence switching
on the motor safely and also preventing line voltage drop.
Here capacitor C1 starts charging as soon as the power is
switched on.
SINGLE PHASING PREVENTER
Many circuits of single phasing preventer or (SPP) are available
but the circuit suggested here is very simple and economical.
Here mains step-down transformers X1, X2, and X3 (230V
AC primary to 0-12V, 500mA secondary rating) are used with
their primaries connected in star mode and secondaries in open
delta mode. The characteristic of this type of connection is that
when three-phase balanced input is applied to the primaries, no
output across open delta secondaries will be available. But in
case of major unbalance or single-phasing, some voltage, called
residual voltage, is induced in the secondary across points 1 and
6 shown in the circuit diagram. Three-phase supply is given to
induction motor through contactor C-1. While the primaries of
transformers X1, X2, and X3 are connected ahead of the
contractor. The contractor can be energized via N/C (normally
closed) contacts of relay RLY-1.
CONCLUSION
Using soft starters for three phase induction motor high
inrush current is considerably reduced and jerks on the
motor during starting can be avoided. The circuit used for
single phasing preventer using the concept of open-Delta is
the cheapest just for rupees 90/- only. Five test readings
are already taken on it and the circuit used for solid
state starter if the cost of contactor is excluded than it
will be only 95/-.So the concept shown in the paper not
only reduces the starting current but also trips the motor
if one of the phases is off. So it is giving reliable and
cheapest solution to the cause.