Size an E-type fuse for 3750 kva transformer, 13.8kv to 2.4 kv?

Manufacturers transformer data should show that. Where are you working with this much power? This is not a DIY project.

So Jim, is it oil filled? Dry Type? Inside? Outside? Does it serve critical operations systems? What country? Utility or private? Is the fuse for the primary or secondary?
and why is the sky blue?

Mineral oil filled, primary fusing? God made the sky blue.

Have you done this calculation yet?
Can you show me your work?