Harish Doshi - It looks like you either have no knowledge, and I might even say no clue about turbine oils, or you have mistaken them with motor or gear oils. FYI, turbine oils are very finely balanced blends, where additives represent only 3-5% or in some cases up to 10%, and the rest is base oil. In any rate, they are definitely not "heavily additized".
As to the original question...
1. Where you see foaming occurs the most, in bearing sumps or a governor sump, or…?
2. Did you folks check (test) and confirm that the new and the old in-service oils are fully compatible, before the changeup? In some cases it has been determined that oils (more precise, additive packages) are not compatible. In such cases, providing you don’t have any air leak, formed flocks would serve as seeds for air entrainment (which you cannot see with unaided eye) and foaming (which you can definitely see).
3. If you did not test for compatibility before you replaced old oil, you may do it afterwards if you have a sample of previous oil and new (unused) oil.
4. Incompatibility can cause stripping of additives (foaming additives included). I would advise you to spend some money and test your new oil (from sump where you experience foaming), and see what happened to foaming and water separation characteristics.
5. Foaming can be nuisance at startup if your oil is cold (thus thick), and therefore, because the rate of air dissipation from oil is greatly impeded (slowed). Does foaming persist even when oil reaches usual operational temp?
6. How sure are you that the oil is clean? What the numbers are saying (ISO 4406/99)? If you only assumed that your oil is clean because it is new, you may be up for a big surprise. It is commonly observed that new delivered oil is much dirtier than your in-service oil. That’s why we filter and dehydrate every new delivered oil, before we add it as a make up oil or use it as replacement oil.