Differential Protection Scheme for Power Transformer Protection

Power transformers are normally protected by differential protection relays. Differential protection is the main protection used for protecting power transformers from internal faults only. External faults have the same effect on the two sets of current transformers used for differential protection. Mal operation of differential protection occurs when an external fault affects only one set of current transformers and causes false tripping. This paper describes how to provide standardized, current based, differential protection for any three-phase power transformer. The primary objective of this paper is to investigate the possibility to use a differential protection for standard three-phase power transformers