catalin78
Before you go jumping in feet first and end up blowing up the drives or the generator, stop and think what you are doing.
What did the crane have on from new?
Have you changed the drives on this crane?
The fitting of a resistor bank to absorb the regenerative energy that the generator cannot handle is pretty standard, the resistors are designed to be switched online at a certain amount of KW regenerative power. The amount of resistance is also calculated, not guessed at.
It seems by what you have written so far, you have voltage and current sensing relays controlling when the resistors are switched online. I would confirm that these are working correctly. These relays probably control a rather large contactor, confirm that this is coming in when the relays are coming in. It might also be worth confirming the state of the contact tips on this contactor.
Has the generator got an electronic management system that displays what the generator is doing? If yes, does it state that the generator is over-volting when the drives are regenerating? Does the generator shut down to protect itself against this over voltage? If what I have stated above is what is happening, I would look at the resistor bank and the contactor and confirm that there is a complete circuit, as an open circuit resistor will cause the over volt problem on the generator. If you switch the resistors online at the wrong time you could end up dragging the generator speed right down, so I would be wary about making any changes to the control circuits unless told to do so by the crane/generator manufacturers.
I have attached a quick drawing of how I think the power side of the genny is set up, it might help explain what I said above.
Paul