Primary protection takes priority: Differential and gas relays must respond first to internal faults. Backup protection ensures full coverage: Overcurrent and zero-sequence schemes protect adjacent equipment if primary protection fails. Differential Protection (87) The most sensitive protection for internal transformer faults: Note: Differential. This guide focuses primarily on application of protective relays for the protection of power transformers, with an emphasis on the most prevalent protection schemes and transformers. Setting procedures are only discussed in a general nature in the material to follow. The problems relating to transformer temperature rise above an assumed maximum ambient temperature require some means of protection. It prevents damage, protects your equipment, reduces downtime, and extends transformer life.
[PDF Version]