What is winding resistance of 247 MVA generating transformer?

it depends the manufaturer standard, nut usaually its above 20 M ohms .

How long is a piece of string? Transformers vary is size hugely, so it's quite impossible to provide a definitive answer to your question. But the resistance of a transformer's windings will be very low -certainly within the ohms or milliohm range, depending on the physical size (cross-sectional area and length) of the conductors. It's most-certainly not in the megohm range, as suggested in the original answer!