Dear Cristian,
Thanks a lot for your reply. It was of course very useful. In this case, no we have not added any oil to the turbine for a while. So the foaming cannot be becuase of new oil or additived being add. I also want to remark that our foaming problem is not that severe. There is foaming visible in the sight glass of the exciter bearings, which was not there before, but there is none in the oter bearings and in the oil reservoir. It is interesting what you mentioned about the Phosphorous because that is a recurrent problem in our oil analysis even in the new oil sample. I did not give to much importance to that because it was not affecting anithing at least that we know of. However, I will contact our oil supplier and ask them about this. Thanks again.