Answer / raju

i think VFDs are next version of soft starters. In VFD we
can varry the speed from zero RPM to Full load RPM. and
come back from Full load RPM to zero speed very smoothly.
But in Soft starters starting will be smoothly but after
reaching the full load speed the Soft starter shall be by
passed and soft starter cannot be controlled the speed.
Cost wise VFD is more costlier than VFD. In reliability
point of vied VFD is better

Answer / j.kesavan

vfd drives adjust the speed what speed we need ,but soft
start only start the motor smoothly up to reach the full
speed.

Answer / purushmallya

VFD is Variable Frequency Drive which works controls the
speed of an induction motor on V/F principle and Soft
starters controls the speed by controling the input volage
with power thyristors.

Answer / mani

VFD is adjustable speed drives.if u vary the pot value,it
can change frequency from 0 to 50 hz,limit amp value.as you
wish.you give information put on VFD,whether its rotate
clockwise and anticlockwise rotation of motor.speed =120f/p.
VFD----convert-ac to dc then dc to ac. then connect motor.
SS-----it has thyristor, connect with motor.its reduced
starting current.but its soft start &soft stop.

Answer / raneesh

Soft starter starging the motor in diarectly. But VFD
giving freequncy in one by one ie howmuch speed requred for
that motor that only giving the VFD. thats why we can
controll the fan speed and power conseption olso.

Answer / shtl

The starting current, will be 6-8 times higher than the
motor's rated current because the motor is at rest.
Those starters reduce or diminish this inrush starting
current are called electrical soft starters.
Soft start is one of the facilities available in VVVF
drives. The other facilities are providing higher starting
torque, speed variation, constant torque maintenance soft
stop etc. Simply saying VVVF drive take care of starting
control, speed control, protection control, forwarding,
reversing control and stopping.

Answer / asif mansoori

VFD is a Drive (continuous controlled operation)
Soft Starter is a Starter (for Smooth Starting torque &
current)

VFD changes frequency applied to the motor and changes its
operating speed.
Soft Starter reduces applied voltage to the motor thereby
reducing the starting torque & hence reduced starting
current.

VFD changes both voltage & frequency.
Soft starter only changes voltage at the starting of motor
but doesn't change frequency.

Answer / paras

vfd used for the speed regulation & soft stsrters are used
for smoothly starting of induction motors. principles &
application of the both is different.

Answer / n.satheesh kumar

By using Soft-Starter to limit or control the starting
currentsource current of the motor.And it provides the
smooth starting for the motor.But in VFD is depending upon
the frequency.

Answer / ramamoorthy

VFD : VFD serves two purpose(smooth starting and speed
control):
a. Smooth starting by gradually increasing the source
power to rated output (by maintaining V/F ratio).
By starting at zero frequency & zero voltage (thus
the starting current also) and gradually increasing
the same to rated value.
b. Controls speed not only during starting but also at
rated voltage.

Soft starter serves only one purpose (Smooth
starting):

a. Smooth starting by gradually increasing the source
power only by increasing the voltage from zero
to full voltage and not varying the frequency like
autotransformer.
b. Cannot control speed at any point of time.

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