A demagnetisation fault detection method for a delta‐connected permanent magnet synchronous machine (PMSM) based on zero sequence current components (ZSCC) is proposed. The model of the delta‐connected PMSM with the demagnetisation fault is first established. Then the expression of the ZSCC is presented for the delta‐connected PMSM, and an equivalent fault severity index which can quantify the demagnetisation degree is obtained, being not limited by the partial or uniform demagnetisation. Finally, the simulation results show that the potential of the proposed fault severity index for the demagnetisation fault detection.