Answer Posted / sumit
VFD acts as a conveter between the motor and main
supply.suppose a motor is carrying a load(coupled to a
pump to lift water )then after sometime load decreases
means requirement of water reduces means pump now needs to
pick less water but torque of motor will have to be same
because pump inertia(m*r*r) and acceleration is constant
stant but now we need to maintain less pressure(to pick
less water) and pressure comes from speed of pump (directly
proportional to motor speed) thus we need to decrease speed
of motor but at the same time as mentioned above constant
torque is must.so decrease voltage to maintain a constant
ratio of voltage/frequency.voltage decreases so currenet
from vfd decreases so line current drawn by vfd from mains
decreases and thus power drawn decreases.and reduction of
speed is done by vfd.
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