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.

is KVAR (not reverse power) relay necessary to protect from excitor field failure on a brushless, synchroneus generator? Some people with previos experince tell me no but the manufacturers tell me it is designed for that purpose. Is it that it is only necessary for brushless generators and not the older style with the slip rings and brushes?

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1. A 380 / 220 V r.m.s. 3-phase 4-wire circuit carries loads of 8 + j8.1 ohm; 4 + j4.1 ohm; and 2 +j2.1 ohmin the three phases respectively. The length of the circuit is 100 m, and the resistivity of the phase conductors is 0.0005 Ω/m. The neutral conductor is of the same size as the phase conductors. a) Select a reference angle 0for the first phase. Then write down the three phase voltages in both polar format and complex number format. b) Make appropriate assumptions, and take temperature effects on resistance is insignificant. Calculate the currents in the three phases. (Note: Determine conductor resistance, and apply Kirchhoff’s Voltage Law) Based on the result, suggest a main switch rating for the circuit. c) Show your preferred direction of neutral current in a diagram, and then determine its value. (Note: Apply superposition principle, and Kirchhoff’s Current Law) Use its magnitude to show that in this circuit, the unbalanced load may increase the voltage drop in some of the phases. (Note: Also observe the common volt drip in neutral) State your assumptions, if there are any. d) Suddenly the neutral wire of the circuit is broken. Estimate the new currents in the first phase, i.e. Phase L1. State your assumptions, if there are any.

0 Answers  

what is the min and max dc voltage for a dc system (110vdc)

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why control circuit voltage always chooses to be 110v and 220v? and in where it is 110v and 220v? and in where it AC and DC?

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how do we calculate contactor and fuse rating for a motor if its full load current is known,i want exact calculation for 1.5 kw motor????

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WHY IS THE UNITY POWER FACTOR NOT THE MOST CONOMICAL POWER FACTOR?

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To avoid arcing what we connect in earthing.

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How is the percentage impedence of a transformer fixed at design stage???

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What are the classifications of heating element?

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how does an energy meter works?

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