VFDs versus Soft Starts

[jaykool]

In general, is it a true statement that upon start-up both VFDs and soft starts have the same charecteristics? VFDs have a delay before delivering full voltage to motor, right?

 

[ron]

They will both reduce the inrush (instantaneous power consumption) on startup when programmed appropriately. The VFD does it by slowly increasing the frequency of the circuit going to the motor, whereas the soft start (depending on the type) will start the motor on reduced voltage.
http://www.mcquay.com/mcquaybiz/literature/lit_ch_wc/Catalogs/Cat-STARTER-6.pdf

 

[dicklaxt]

Soft start as I understand it can mean the use of either the VFD tecnology or the star delta starter.

The VFD needs to be connected with a VFD cable that has 3 ground wires equally spaced in the interstices of the cable to combat harmonics. The star delta starter has 3 contactors and 6 power conductors need to run from the starter to the motor.

I don't specify but am glad to see the VFD used over the star delta,,,,,actually star delta is old school and even tho VFD's have been around for years they are getting better and better with cutting edge technology while star delta is setting stagnant IMO

dick

 

[winnie]

Soft starts and VFD will both reduce the voltage going to the motor. But a very significant difference is that a VFD will also reduce the frequency. This frequency control lets the motor develop full torque over the entire starting operation, even though the voltage and power is reduced.

With a soft start, the reduced voltage means greatly reduced starting torque.

-Jon

 

[jcole]

You might already know this but wye delta and electronic is not the only way to reduce voltage at start up.

Impedence, reactor, and autotransformer are other types of ways to reduce voltage at start up.l

 

[cadpoint]

VFD's

VFD's

On of my first try's on the pictures.

...

Just three wires in and three out...