Conference Paper

Characteristic signature identification of air-gap eccentricity faults using extended d-q model for three phase induction motor

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Abstract

The supremacy of three phase squirrel cage induction motors in industrial drives demands accurate and reliable diagnostics for condition monitoring and internal fault detections. Operating stresses on these machines are electrical, mechanical, thermal, magnetic and environmental in nature and might result in internal faults. Avoiding unscheduled maintenance and repair intervention can prevent losses in money, material, manpower and time in process industries. Detection of faults in its early stage becomes an indispensable need especially in critical applications. Mathematical model based simulation studies will support fault signature identification to a great extent. Conventional d-q model of AC machines are not generally used for internal fault diagnoses. In this paper a novel attempt is made for simulating eccentricity related faults by modifying conventional d-q model of three phase induction motor. Characteristic fault signatures were identified in the stator current frequency spectrum for static, dynamic and mixed eccentricity conditions. The increase in magnitudes of these characteristic frequency components with increase in severity of faults is also established through model based simulation studies. The experimental study results presented for static eccentricity in a three phase squirrel cage induction motor clearly validates the modelling approach.

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... The term of the end ring current from the rotor electromagnetic equations in (8) is removed to give Equation (8) a symmetric structure. Considering the assumption above, the MCCM can now be transformed into a two-phase model [32]. ...
... Therefore, with the same degree of eccentricity, the amplitude of the characteristic current component under no-load operation and rated load operation are almost the same. This is consistent with the experimental results in [32]. ...
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The motor current signal analysis (MCSA) technique is widely used as a non‐invasive method for detecting mechanical faults in induction motors by capturing characteristic components in the stator line current. However, the threshold of the characteristic component is not clear now, which makes it difficult for MCSA to judge whether the fault occurs or evaluates the mechanical fault severity. The existing model‐based evaluation methods cannot meet the requirement of online condition monitoring because of their slow calculation. To solve these problems, a simplified dynamic motor model under any type of mechanical fault is established, and a formula for the amplitude relationship between the radial vibration of the rotor and fault‐related component in the stator line current is derived. The radial vibration amplitude is related to mechanical fault severity. Using this formula, the MCSA technique can rapidly evaluate the mechanical fault severity according to the amplitude of the characteristic component in the collected stator current. The simulation study results demonstrate the accuracy of the simplified model and formula. The experimental results presented for condition monitoring in a real induction motor clearly validate the evaluation approach.
... Also, an accurate model can be used in model-based fault diagnosis systems to directly identify the fault severity [15]. An attempt has been made for simulating eccentricity faults by modifying conventional d-q model of three phase induction motor in [18], however, this method suffers from rough assumption of sinusoidal distribution for the stator and rotor windings. Multiple coupled circuit model (MCCM) based on the modified winding function theory, also known as the winding function approach (WFA), is the other analytical method for modeling eccentric SCIMs. ...
... 18)-(19) are written by considering that the turn functions of the stator windings are independent of the rotor position and the z-coordinate. The equations versus θ to get exact equation for the derivative inductances to be used to calculate the induced torqueFig. ...
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