Transformer Protection - Coordination

[sky2020]

Can a secondary transformer breaker protect a transformer? or it is only a relay in the transformer secondary can open the upstream primary breaker ?

Do we need a coordination between primary and secondary breaker? Does the secondary breaker protect the thermal curve of a transformer?

 

[RRaghunath]

Secondary breaker can protect the transformer against overload.
Transformer secondary windings are provided with Restricted Earth Fault (REF) Protection - 87N, in case of HV windings. In such a case, the 87N opens the upstream breaker.
Coordination is not necessary between upstream and downstream breakers for overcurrent faults as long as the protection scheme can identify whether it is downstream fault or the transformer fault that caused upstream breaker to open.
Temperature protection and thermal overload protections can be wired to open only the secondary breaker. This is practiced by some utilities.