Two 250 VDC 1200A rectifiers feeding multiple crane rails - is it OK to put the outputs in parallel ?

[bdn2004]

A new installation is being put into this Plant that is a copy of another just like it: as described.... (2) 300 kW rectifiers feeding the power to multiple crane rails.
The rectifier vendor is not recommending this saying:

"You cannot connect two of these rectifiers’ outputs in parallel. They will not share current equally. Please confirm."

The other system just like it has been there for decades. Is the vendor correct ?

 

[waross]

So despite what the vendor is saying, do you really want to depend on advice from an anonymous source on the internet?
Wasn't there recently a discussion of a massive grid failure in Australia due to two rectifiers being in parallel?
Let us know how it turns out for you.
OR
Ask the vendor or manufacturer if the rectifiers may be modified so as to work and play well together.
There are control schemes that naturally lend themselves to paralleling seamlessly.
There are other control schemes that are not suitable for parallel operation.

 

[AG-PPI]

I am assuming the rectifiers are standard 3-phase AC to DC?

I'm a little rusty but I believe you can connect the DC outputs in parallel to share the load, but it is not as simple as shown in your diagram
The AC input on one rectifier must be delta, the other must be star. They cannot both be delta as shown in your diagram, and will need to be fed from a 6-phase transformer.
One major consideration is whether or not you intend to use an IPT on the positive outputs or not.
This will affect the DC voltage output as well as AC input current.

This method would require a control board for such operations.
I would personally recommend the FCOG1200 6-ph firing board from Enerpro in the US, but it would be well worth discussing specific needs with them directly. They are usually very helpfull and open to custom board modifications. (Company I work for uses them a lot, always been very happy with them).