what is the working principle of soft-starter & how it
diff. from VFD ?????????

Answer Posted / phanindra kumar .m

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.
Where as by using VFD,we can control both voltage and
frequency,so speed control is possible above and below Ns.

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