Turn to Turn Short-Circuit Fault and High-Resistance Connection Diagnosis for Induction Motor During Start-Up Transient

In this paper, a new method to diagnose turn-to-turn short-circuit faults (TSCFs) and high-resistance connections (HRCs) for soft-starters fed squirrel cage-rotor induction motors (IMs) is proposed. TSCF and HRC faults cause a significant temperature increase if not early detected. TSCFs requires immediate IM shutdown, whereas the effects of HRCs can be monitored over time. Several methods proposed in the literature are based on zero-sequence voltage or negative-sequence current for fault diagnosis. Most of them were applied for steady-state conditions and only consider sinusoidally distributed windings, without including harmonic components. The proposed method is based on monitoring the fifth harmonic current during the start-up transient to separate the effects of TSCFs and HRCs. Two new analytical models with fault considering the h-th harmonic in the supply voltage are proposed. The first IM model incorporates the effects of a TSCF in any of the phase windings, while the second considers an HRC fault. Based on these analytical models, two indicators are proposed to quantify the severity of the faults. Both indicators are defined from the positive-sequence component of the stator current and allow decoupling the effects between the TSCFs and the HRCs. The practical implementation was carried out with a standard soft-starter, without modifying their control algorithm or internal structure. In the experimental tests, an IM with modified windings was used to generate short-circuits between 3 and 10 turns. On the other hand, the HRCs were generated by connecting resistors of different magnitudes in series with a phase winding. The experimental results demonstrated that the positive-sequence current component of the fifth harmonic exhibits different patterns in the presence of a TSCF or an HRC.