Back energisation is not same as Inadvertant energisation as we use in India. Back energisation refers to energising the generator transformer from HV side with generator connection (or Generator LVCB, if relevant) open.
The relay CAG 37 is Instantaneous OC relay, used for short-circuit protection. In this case, the relay can protect the system in case of faults on the HV side of the transformer, including the bushings and cable / overhead line.
Trust the above helps.