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

2. The differential protection of the oil-immersed transformer is the main protection of the transformer, and the gas protection is the main protection of the internal fault of the transformer.

3. The scope of protection of oil-immersed transformers is different:

3.1 Differential protection of oil-immersed transformer:

1) Multi-phase short circuit occurs in the main transformer lead wire and transformer coil.

2) Single-phase serious inter-turn short circuit.

3) Protect the grounding fault of the coil and the lead wire in the high-current grounding system.

3.2 Gas protection of oil-immersed transformers:

1) Multi-phase short circuit inside the transformer.

2) Inter-turn short circuit, inter-turn and iron core or outer and short circuit.

3) Iron core failure (heating and burning).

4) The oil will leak or leak under the oil level.

5) Poor contact of the tap changer or poor wire welding.