1. The differential ochrana of the main transformer is designed and manufactured according to the principle of circulating current, while the gas ochrana is designed and manufactured according to the characteristic that gas will be generated or decomposed when the transformer internal fault occurs.

2. The differential protection is the main protection of the transformer, and the gas protection is the main protection when the transformer is internally faulty.

3. According to different protection scopes: A Differential protection: 1) Multi-phase short circuit occurs in the main transformer lead wire and transformer coil. 2) Serious turn-to-turn short circuit of single phase. 3) In the large current grounding system, protect the grounding fault of the coil and the lead wire. B Gas protection: 1) Multi-phase short circuit inside the transformer. 2) Inter-turn short circuit, inter-turn and iron core or external and short circuit. 3) Iron core failure (heating and burning). 4) There will be or oil leakage under the oil surface. 5) The tap changer is in poor contact or the wire is poorly welded.