Solid State Transformer

alfacliff

Joined Dec 13, 2013
2,458
non solid state soft starts are usually resistors switched in series with a motor by relays, solid state soft starts are modified VFD's that bring up the frquency slowly to limit motor starting current.
 

MaxHeadRoom

Joined Jul 18, 2013
28,617
One 'regular' older method was to use star/delta switching to bring a large motor with a load up to speed reducing the starting current, the S.S. is as alcliff mentions, rpm is brought up to speed by V.F.
Another sometimes seen was series inductors inserted into the line on start.
Max.
 

alfacliff

Joined Dec 13, 2013
2,458
there are also soft starts for large VFS's, a resistor is placed in series with the charge line for the capacitor bank after the three phase rectifyer to reduce the huge start current of a whole door full of 6000 mfd caps in paralell on one brand.
 
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