I. Common Faults and Abnormalities in Transformers Transformer faults can be categorized into internal and external faults.

Internal faults refer to failures occurring within the tank enclosure, including phase-to-phase short circuits in windings, turn-to-turn short circuits within a single phase winding, short circuits between windings and the core, and broken wires in windings. External faults encompass various phase-to-phase short circuits between the transformer's external leads, as well as single-phase ground faults caused by flashover through the insulation bushings of the leads to the tank enclosure.

Transformer failures pose significant hazards. Particularly during internal faults, the high-temperature arcs generated by short-circuit currents not only burn through the insulation of the transformer windings and damage the core but also cause the transformer oil to decompose under heat, producing large volumes of gas. This can lead to deformation of the transformer casing or even an explosion. Therefore, faulty transformers must be isolated immediately. Abnormal conditions in transformers primarily include overloads, low oil levels, overcurrent caused by external short circuits, excessive oil temperature during operation, excessive winding temperature, excessive transformer pressure, and cooling system failures. When a transformer is operating abnormally, an alarm signal should be issued.

II. Configuration of Transformer Protection
Primary Protection for Short-Circuit Faults: Primarily includes differential protection and heavy gas protection.
Backup Protection for Short-Circuit Faults: Primarily includes composite voltage-locked overcurrent protection, zero-sequence (directional) overcurrent protection, and low-impedance protection.
Abnormal Operation Protection: Primarily includes overload protection, over-excitation protection, light gas protection, neutral gap protection, and temperature/oil level/cooling system fault protection.