Detection and Diagnosis of Broken Rotor Bars in Induction Motors Using the Fuzzy Min-Max Neural Network

2.1. Theory

Cast cage and fabricated cage are two different types of cage rotors in induction motors. Cast cage rotors are normally used in induction motors up to 3000-kW rating while fabricated cages are used in induction motors of higher ratings and in special application machines (Awadallah & Morcos, 2003). Cast rotors are difficult to fix once breakage or cracks develop in them, although they are more durable and rugged than fabricated cages. According to Montanari et al. (2007), broken rotor bars constitute about 10% of the total induction machine faults. During broken rotor bars events, the sideband currents are given by (Awadallah & Morcos, 2003):

Where k = 1, 2, 3. Considering the speed ripple effects, other frequency spectrums, which can be observed in the stator-current spectrum, are given by (Awadallah & Morcos, 2003):

Where p is the number of pole pairs, and k/p = 1, 2, 3.