Star - Delta with two motors

[0831]

My Problem is this: I have two 150kw 3ph motors sharing a multi belt rotor, i need to wire this so that one motor starts in star which means the other motor is turning with it at the same speed then when the delta contactor/s kick in BOTH motors will be powered in delta, do i achieve this with one star contactor and two delta contactors? or just up the size of the whole star delta set of contactors to take the fla of both motors in delta and wire the delta side of both motors to the delta contactor?

 

[0831]

I guess nobody has an answer?

 

[jraef]

In general, Star-Delta starting is risky at best to use on one motor. Doing what you intend is something I would never think of; the risks are not worth the benefits.

But if you insist, you cannot run 2 motors from one starter circuit anyway, unless you have separate sort circuit and overload protection devices anyway. In that case, what are you saving here by trying to use only one larger contactor? You would still need to have another SCPD and OL downstream in that case. Nothing saved.

If you insist on using Star-Delta, just start motor #1 with it, and then have a separate DOL starter for motor #2, closing that contactor only after the Delta contactor is closed. I would use a soft starter and start them both behind the soft starter, with separate MCCBs and Overload Relays downstream. In the IEC world (assuming you are there because you used kW instread of HP), you can likely get an MCCB with an adjustable thermal OL built-in.