Abstract: Aiming at the problems of complex operation, low reliability, and easy loosening leading to equipment damage in the traditional secondary winding short-circuit methods (flexible copper wire, alligator clip) during the insulation test of 35 kV and above transformers in substations, a new type of quick short-circuit device for substation transformers was designed. The device consists of three parts: A quick-detachable short-circuit device body, a short-circuit socket with built-in copper plate, and a grounding device with male-female connectors. It integrates innovative designs such as a stud quick-locking cap (with strong magnet), multi-tap banana wire, and spring copper sheet contact structure to realize fast positioning, firm connection, and safe grounding of the secondary terminals of the transformer. Field tests and application verification show that the device can shorten the short-circuit operation time of a single group of terminals from the traditional 15 min to 5 min, reduce the loosening rate to 0%, and no equipment damage risk occurs in scenarios such as withstand voltage tests. It significantly improves the transformer operation and maintenance efficiency and test safety, and has broad engineering promotion value.