Direct Online Starter (DOL)? Working Principle and Advantage and Disadvantage of DOL Starter
Associating little motors to a power gracefully by the type
of attachments and switches don't require any extra advance for turning over
the engine. Nonetheless, the acceptance motors of high power require an
appropriate gadget for the beginning since they take an unreasonable measure of
beginning current. There are different beginning techniques utilized for
turning over enlistment motors since Induction Motors draw exceptionally high
beginning current (5-7 times more) contrasted with the full load current of the
engine when it's begun.
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In this manner, to maintain a strategic distance from
the engine from burnout and warming because of the high benefit of a beginning
current, different kinds of starters are utilized for turning over enlistment
motors. The sort of gadget utilized for turning over the acceptance engine is
known as the Direct ON-Line Starter (DOL). Direct ON-Line starter is the least
complex sort of starter that interfaces the engine directly to the power
flexibly through a three-stage cont actor. The Direct on Line Starter, as a
rule, comprises of a Cont actor, Circuit Breaker, and an Overload hand-off for
security against any harm.
The DOL starter fundamentally comprises of two principle
assurance parts
• Over current
Protection
• Overload
Protection
An Electromagnetically worked contactor is utilized which
can be opened by warm overload transfer at whatever point an issue condition
happens. Contactors are regularly going to be constrained by discrete beginning
and stop catches, and there is likewise an extra contact on the contactor that
is utilized over the beginning catch as hold in contact. For instance, the
contractor utilized is electrically hooked based and shut while the engine is
working.
Over current Protection:
Over current shortcomings happen for the most part and
chiefly because of ground blames and short out flaws. Along these lines, wires
and circuit breakers are utilized that show snappy reaction towards issue when
such sort of flaw (huge) current goes from the framework. That is the reason to
shield the framework from the short circuiting and furthermore from the
overload current we utilize MCCB's or Fuses of explicit evaluations.
At the point when the measure of current bigger than the
evaluated current of the gadget went through the framework such gadgets work
and open the circuit until the issue is expelled from the framework. We can
likewise say that when a little higher measure of current past the rating of
engine pass Overload security begins working and keep the machine from any
risk. In the event that the overload current perseveres for a long-range of
time, at that point, things and machines get harmed.
Overload security doesn't
trip regardless of whether a high estimation of current streams for a limited
capacity to focus time, for example, the turning over of the engine.
Overcurrent assurance rating is constantly chosen with so much consideration
that it must give enough security against high current and furthermore it must
permit enough current without working the overcurrent insurance for the engine
to work under substantial mechanical load.
Overload Protection:
At whatever point engine draws an excessive amount of
measure of current to satisfy the load request and if the load request goes
past as far as possible, such condition or circumstance is called Overload. An
electric overload happens when an unnecessary measure of current goes through
electric wires or from engine wingdings. The wires or winding can warmth and
liquefy, with the danger of lighting a fire. Hence, overload insurance is
utilized in it.
It is essentially a sort of security insurance when the engine
draws an excessive amount of current or overload current and causing the
overheating of the electrical machine. With the goal that's the reason, we
utilize an alternate sort of overload transfers to maintain a strategic
distance from the framework or machine from overheating because of the
unnecessary measure of current drawn for a really long time period. Once in
awhile engine starters accompany worked in overload transfer.
Overload transfers are arranged on the base of various
stumbling classes. Stumbling class is a term utilized in overload transfer
planning which implies how much seconds an overload hand-off takes to trip.
Overload insurances are furnished with the assistance of an overload transfer.
Overload transfers utilized here are of different sorts.
• Electronic
Relay: Overload might be a strong state gadget having a flexible excursion
setting referenced on them likewise called the electronic transfer.
• Thermal
Relay: If they are interfaced with temperature sensors it is called a warm
transfer.
• Magnetic
Relay: And on the off chance that they just work for a high measure of current
stream, at that point, it is called an attractive transfer. The greatest rating
of the overload assurance gadget is 125% of the full load current rating for
most extreme motors.
Development of DOL Starter :
DOL Starter essentially includes just two catches one of
them is 'green' and the other is 'red'.' Green button is utilized for beginning
and 'Red' button is utilized for halting the engine. The Direct ON-Line Starter
really comprises of a cont actor, an MCCB or electrical switch, and an overload
transfer for security at whatever point a shortcoming condition happens.
The
previously mentioned two catches 'stop' and 'start' or additionally called
'Red' and 'Green' catches are utilized to control the contacts. For turning
over the engine, we press Green Button and the contact is shut and along these
lines, full line voltage begins showing up over the engine. a cont actor can
either comprise of 3 posts or 4-shaft rely on the plan. For our situation, the cont actor utilized is of 4-post type.
There are three "Ordinarily
Open" contacts from where the engine is associated with the graceful
lines, and the fourth one contact is called "hang on contact" which
is an extra contact and this one empowers the cont actor curl after the
beginning or green catch is discharged. The extra curl gets de-invigorated in
the event that there is any shortcoming happen and, at that point, starter
detaches the engine from flexible mains.
Working of DOL Starters :
(I) DOL starter wiring association with start and stop
catches are appeared in the above figure (1). Between the mains gracefully
terminals and engine terminals the DOL starter primary terminals are associated
and with the two terminals of the three-stage power flexibly as depicted in
figure (1) the control circuit is invigorated.
(ii) Current will move through one stage to the control
circuit and the cont actor loop to the next stage when the beginning catch is
squeezed. Cont actor loop gets stimulated because of this current that makes to
close the contacts of the contactor and in the aftereffect of this three-stage
gracefully is associated with the engine. The beginning catch is now and then
called as press button since when this catch is discharged the control circuit
of DOL starter despite everything give the power flexibly by means of
Hold-On-Contact. The current way by means of contactor loop will break when the
stop button is squeezed and because of this the contactor contacts drop out,
along these lines breaking the power gracefully to the engine. We can likewise
say that the overload hand-off curl works.
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(iii) Depending on the warming impact of the load current
warm overload insurance transfer works in light of the fact that the warming
impact is directly relative to load current. More the load current more is the
warming impact. Spring loaded contact in the control circuit trips out just
when bimetallic strip utilized inside it grows because of warmth. This all
happens when the measure of load current is an excess of that it can warm the
warm curl. Hand-off working velocity is characterized by current modification.
Ordinarily it must be 3-5 times the appraised current of the engine.
(iv) Remotely worked DOL starters are likewise utilized for
control the exchanging of the engine from any ideal spot. In any case, there is
a condition for remote control based exchanging that one should know, that all
the remote "OFF" press fastens consistently be associated in
arrangement with "OFF" push buttons of the starter and the other way
around (all the remote "ON" press fastens consistently be associated
in corresponding to "ON" push button of the starter).
Advantages of DOL Starters :
2. More
agreeable, easy to work and control.
3. The
control circuit is a lot less difficult.
4. Very Easy
to investigate and effectively reasonable.
5. Direct on
Line starter gives 100% torque at beginning.
6. From
starter to engine just one lot of link is required.
7. It
interfaces the gracefully to the delta twisting of the engine.
8. The size
of DOL is smaller to the point that is consumes less space.
Disadvantage of DOL Starters :
1. The
beginning current of the engine doesn't diminish.
2. Direct ON
Line starter has high beginning current or an excess of current 6 to multiple
times of full load current.
3. Due to
the enormous warm weight on the engine, the life expectancy of the machine
lessens.
4. There is
a noteworthy plunge in voltage in the electrical establishment on account of a
lot in-surge current and because of this other client associated with similar
lines influenced, henceforth this is reasonable just for little motors.
5. The
mechanical weight on the mechanical frameworks is expanded on account of
pointless high beginning torque, in any event, when not required by the load
and this is extremely hazardous for machine life.
6. DOL
starter is just appropriate for motors of rating under 10kw.
7. DOL
starter inconvenience is that it gives the most elevated conceivable beginning
current.
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