Abstract: An improved internturn short circuit detection device of transformer via differential voltage comprises a single-phase transformer (TM). The single-phase transformer (TM) comprises a high-voltage coil (K) and a low-voltage coil (N). A voltage transformer (PT) is positioned at the high voltage side of the single-phase transformer (TM). Two branches of a tap (K1) of the high-voltage coil (K) are connected with the input of a first converter (Q?), and a first voltage (U1?) is obtained. The secondary side of the voltage transformer (PT) is connected with the input of a second converter (Q), and a second voltage (U1) is obtained, and the first voltage (U1?) and the second voltage (U1) are compared, and when the voltage difference is above a predetermined primary threshold value, an interturn short circuit failure of the primary side is determined.