Answer / rvg

Variable frequency devises not making use of any
contactors, since the speed and rotation reverse can be
done with the circuit itself.
VFD having control of supply frequnecy and speed can be
changed with that.

Answer / revansiddappa p.h.

Basically contactor is used to make and break the circuit
like any switch. For handling higher current and volatge we
use contactor; not only for motors.
Between VFD and motor; contactor is not required.
Because VFD will have features like enable and disable.
VFD will use IGBT's inside for switching application.
As IGBT's are semiconductor ; switching is fast compared
to electromachanical type contactor.And IGBT's handles
larger currnts.By enabling or desabling of VFD we can
Start/stop motor(with speed command). If contactor is used
there will be some time difference in swithcing ON/OFF of
IGBT and contactor which may lead to failure of IGBT and
motor winding and insulation. So it is meaning less to use
conatctor and also cost will be more.

Answer / nandan d shanbhag

Due to electromechanical bouncing of the contactor
contacts , voltage spikes are generated which in turn will
result in failure of smiconductors in the drive. However
due to eletrical regulaton if contactor needs to be
provided for electrical isolation then there must be delay
of 1 sec before starting the inverter after contactor is on
and contactor should be made of atleast .5 second after the
inverter is made off.

Answer / shailesh

vfd is a variable frequency drive,which not provided
contactor because there use a thyristor.

Answer / jayaseelan

This will cause unnecessary wear on the contactor and
there will always be a slight delay while the inverter
initialises.ie.if contactor placed in between vfd and motor
response time of contactor gettting on is slow compare to
vfd response speed so return current wii affect the
electronic bords.thats y contactors not not used in output
of vfd.

Answer / jayaseelan

This will cause unnecessary wear on the contactor and
there will always be a slight delay while the inverter
initialises.

i want to model paper for section engg.

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i am swathi, b.tech 4th year. In smps(switched mode power supply)we are using diodes,mosfets,igbts for controling of current. And my question is why we did not use thyristors(scr)? it is also act as a switch,then what is the drawback of scr as compared to above transisters> if we use the scr,then what is happening ? plz give reply as soon as possible bcoz i am doing project on smps. plz frnds i want ans for that. if anybody know the ans plz send to my e-mail id /swathi.tadakapally@gmail.com/

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