Refer to NEC art 450.
Your question does not indicate that secondary protection has been provided and as such I would assume that the transformer is 3ph with a 3w delta secondary or 1ph with a 2w secondary. As such a properly sized OCPD can be provided on the primary side.
Should a properly sized secondary OCPD be provided then it is that device that protects the transformer form overload. Please not that a secondary OCPD is mandatory with 3ph4w and 1ph3w secondary?s.
When a secondary OCPD is provided then the primary device no longer need s to provide OL protection and it is already being provided then the primary OCPD essentially provides short circuit protection should the transformer fail taking it off line to protect the upstream distribution system.
