On "Steven's Technical List" under the tools menu I have posted links to two publications (Siemens Power Engineering Guide and Alstom's NPAG). Both of these contain recommended protection schemes and guidance for the protection of various items of equipment.
I would start by looking at these, thinking about any suggested options which may not be relevant to your case or anything special about your case which may necessitate additional protection. Given there is cost issue with protection, you should also tie this with the type of protection relay(s) you intend using. By working through this I you will be able to come up with a suitable scheme.