This document discusses power transformer protection. It begins by explaining that transformers are static devices that transform electrical energy between circuits without changing frequency. Power transformers are vital but expensive components that are difficult to repair if damaged. Protection is needed to prevent severe damage from faults. It then describes the types of faults as incipient, internal, or external. Potential causes of faults are listed as insulation breakdown, overheating, oil contamination, reduced cooling, and phase/ground faults. The document outlines the general scheme of differential protection and lists specific protection functions used. It provides an example calculation for setting a transformer differential relay and describes the relay's operating characteristics. Models of differential protection relays from various manufacturers are also listed.