A simple and robust sensorless technique for on-line stator winding turn fault detection based on monitoring an off-diagonal term of the sequence component impedance matrix is proposed in this paper. Due to the destructive and rapidly propagating nature of insulation failure, it is critical to detect turn faults in an early stage to minimize the financial loss. The motor non-idealities such as the variation in the supply voltage unbalance, slip-dependent influence of inherent motor asymmetry, and measurement errors must be taken into account in order to reliably detect a turn fault in its incipient stage. Simulation and experimental results on a 5 hp induction machine are given to confirm the validity of the proposed method. It is shown that the proposed turn fault detection scheme is simple and is capable of providing reliable fault detection that is immune to the motor non-idealities.