Design a single-phase / three-phase transformer designed for voltage detection unit of 400Hz frequency ship converter excitation regulator. Transformer has asimilar structure to AC motor, but the rotor is fixed, a single-phase AC power pass into the rotor and three-phase alternating current generated in the stator side. The transformer is used to the detection circuit of voltage regulator , so that the filter capacitor can be reduced, thereby reducing the latency of signal feedback and improve the response speed of the excitation regulator. The experimental results show that, the transformer has obvious effect on improving the response speed of the circuit.