That thing up there is a "cut-out fuse" on the primary.
See:
https://en.wikipedia.org/wiki/Fuse_cutoutDon't know if that particular transformer has any secondary protection, but if you look at the product literature from distribution transformer manufacturers, there are options for integral primary and secondary protection (e.g. a breaker on the secondary). Of course there are external protection options as well.
A good example of available protection options is in:
http://www.powerpartners-usa.com/wp...otection_package_spec_sheet-1.pdf?x39528With that said, I don't know what's most common, but now that you've raised the question, I'm going to be looking up a bit more when walking around.