Answer / pushpendra kumar

Variable frquency Drive, principle of the same is by
regulating the frequency, we can regulate the speed of
drive

Example - n=120f/p

Where,

n - speed
f - frequency
p - nos of poles

By the equation we can calculate the all parametes shown
above.

Answer / virendra

In additon to what Pushpendra said VFD mean variable
frequency drive ( means a speed control my controlling
frequency ) as N= 120*F/P

If the frequency is decreased flux will increase hence
speed will decress . at the other hand if frequency will
increase flux will decrease & speed will increase...

Answer / ganapati.s.h

A softstarter is replica of a star-delta starterin which
starting current is controlled by reducing voltage using ac
voltage controller for smooth starting.As Ac voltage
controllers are not suitable for speed control.So,soft
starters are mainly used for starting purpose only.(since
in Ac voltage controller,frequency is fixed,only voltage
has to be varied.Also,It produces predominant harmonics
into the system.
You can divide the world of electronic motor drives into
two categories: AC and DC. A motor drive controls the speed,
torque, direction and resulting horsepower of a motor. A DC
drive typically controls a shunt wound DC motor, which has
separate armature and field circuits. AC drives control AC
induction motors, and-like their DC counterparts-control
speed, torque, and horsepower.

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