It is indeed 2000A at 900 volt. It is a motor used to drag a 20 tonne bucket in a coal mine. The measurement is tobe done only for monitoring and not protection. I have to decide whether the bucket is 20% filled, or 40%, 50% ... 100%. There are three such motors - one for dragging, one for lifting, one for swinging. It is a huge system known as a dragline. I think a response time of one second is enough in this case.

I am thinking to use a separate linear 12V supply (Transformer-rectifier-7812)whose 0 volt will be connected to negative of the 75mv signal. The MCU supply will also be linear but through a separate transformer.
I have not seen the 900V supply and do not know whether it is a thyristorised converter or a simple rectifier.
Unmesh