Answer / debashisdb

Most Industrial drives have variable speed application
(fans, pumps) where the initial speed of the load is
normally very low and increases gradually.
The induction motor used for the purpose will have
specified starting torque & speed as per the torque-speed
curve of the motor. The speed is normally very high
compared to the load requirements at start. So by vfd it is
possible to control the speed of the motor according to the
loading requirements.
Since Power is proportional to cube of speed, control of
speed saves a lot of power requirement.

Answer / jayaseelan

usually torque is inversely proportional to speed in normal
application.

for particular application ony we can reduce the power
consumption ex.fans,extruder,pumps etc
Some loads have a Variable Torque characteristic, that is,
the torque increases with the speed.torque increases means
current increse also speed increases so if speed reduce
means torque reduce consquently current reduce this is the
concept.
usually torque is inversely proportional to speed in normal
application.but some cases ex.

Answer / op singj

S=120f/p so speed prapotional to frequency.when motor running is rated speed then takes rated current.if we have requirement low speed of motor than we can reduce frequency according rwequirement load or speed.VFD works on frequency according load we can speed increase or decrease by frequency increase or decrease.Thanks.

Answer / ashish umrao

vfd use only variable freqancy derive moter speed proposnal
to the freqancy ns=120f/p if freqancy is vary to moter speed
also vary ,speed touqe is inversaly prosnal to each other.if
speed is high ,touqe is low &vise versa.current is proposnal
to the load is cunnected so load is high current high and
touqe also high.if can change the sutable ferqancy to save
the energy.

Answer / selvaraj

1. the filter capacitors that are used in rectifier portion
of the VFD helps in boosting the power factor of the
substation.

2. in a motor electrical energy is converted into
mechanical energy. ie.
electrical power = rt3VICOSINE ANGLE
mechanical power = 2*3.14*N*T


By using VFD variable TORQUE and variable SPEED can be
achieved.so by reducing the mechanical power electrical
power will also be reduced in the same ratio.

the cheapest inducting instrument among all is a)pmmc b)moving iron c)electrodynamometer d)rectifier

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