Dry-type transformers are widely used in local lighting, high-rise buildings, airports, and wharf CNC machinery and equipment because of their good overall rigidity, strong ability to resist sudden short circuits, energy saving, and suitability for harsh environments. The normal working conditions of dry-type transformers are overload, overcurrent caused by external short circuit, neutral point overvoltage caused by external ground short circuit, oil level drop caused by oil tank leakage or temperature rise caused by cooling system failure. In addition, due to the high rated working magnetic flux density of large-capacity dry-type transformers, which is proportional to the voltage-frequency ratio, over-voltage or low-frequency operation may cause over-excitation failures of dry-type transformers. According to its own characteristics and working conditions of dry-type transformers, it usually adopts the following protection methods:

1. Gas protection: It is used to reflect various failures of the oil tank of the dry-type transformer and the reduction of the oil level.

2. Longitudinal differential protection, current quick-break protection: used to reflect the faults of dry-type transformer windings, bushings and outlets. The instantaneous action of the protection is to open the circuit breakers on each side of the dry-type transformer.

3. Phase-to-phase overcurrent protection: According to the operating conditions, composite voltage blocking and direction blocking can be introduced. According to the setting requirements, it can reflect the internal and external phase-to-phase short-circuit faults of dry-type transformers, as the protection of gas protection and differential protection (or current quick-break protection). backup protection. After the protection action, a time limit action should be taken to trip.

5. Zero-sequence current protection and zero-sequence current direction protection: According to the setting direction, it can effectively reflect the internal and external single-phase grounding short-circuit faults of the dry-type transformer.

6. Overload protection: reflect the overload state of the dry-type transformer, and act on the signal or trip.

7. Over-excitation protection: Reflect the over-excitation state caused by over-voltage or frequency reduction, and act on the signal or trip.