Soft Starter Rating for 700hp 4.16kV Motor

[Askarel27]

Our Client is adding 700hp 4.16kV Squirrel Cage Motor for Compressor. Then Vendor quote 400A Bus rating and Current Rating is 110 A. How is the Soft Starter rating is selected? Is their a chart or code define the sizing of the Soft Starter Controller. Please help

Additional Data:
Motor is S1 Duty, Class B Temp Rise, 4000V, 60HZ, 3583rpm, 86 A, 522kW.

 

[jraef]

Soft starters are rated for the current of the motor nameplate power, just like any other starter is, so I guess I don't see your problem here. Rating of a bus bar that is FEEDING a starter has little to do with the rating of the starter, other than it must be equal to or greater than the starter rating of course.

That said, MV solid state soft starters use vacuum contactors for line isolation and bypass. Most vacuum contactors come in only a small number of ratings at 5kV class, 200, 400, 600, & 800A are typical nominal ratings. The power SCRs are also similar, but may have even fewer choices, for example 160A, 320A, 800A. Then lastly, the contactors and SCRs are required to be coordinated with MV "R" type fuses, which again only come in certain sizes. So when you buy a sold state soft "starter", the rating of that starter is a combination of all of the convergences of those possibilities that work for the MOTOR data that you provide to the vendor. So we really come back to my initial statement; soft starters are rated for the current of the motor nameplate power.

"Will work for (the memory of) salami"

 

[nkn5]

While agreed mostly with jraef, the rating selected here looks okay. motor full load =~72 Amps. so rating of 110Amps is suitable.

Regarding controller, you will have to verify the type of controls available in the soft starter. For example, voltage control / current control, current limiting, etc. The effect of starting need to be verified by using a electrical analysis software before proceed to purchasing the soft-starter.