Stator Current Of Induction Machine Research Articles

Early Diagnosis of Induction Machine Stator Winding Faults by Discrete Wavelet Transform

AbstractElectrical machines are useful in nuclear power plants, military applications, domestic appliances and industrial utilities. The relevant literature indicates that the induction machine takes about ninety percent of all electrical machine globally used in the industry. The risk of the failure of this machine can be avoided if the proper diagnostic scheme is designed and implemented to detect failure/impending faults at an incipient stage. This paper describes Discrete Wavelet Transform (DWT) based diagnosis technique that analyses stator currents of induction machine under healthy and faulty conditions. This enables the extraction of harmonic components caused by each signal for further analysis. On one hand, the maximum energy for each signal gives information about the time a certain fault occurs in the machine and the time it starts deviating from the normal (healthy) state. On the other hand, a Fault Index (FI) is generated for each situation in order to classify the state of the machine into normal, medium or high. The colours; green, yellow and red are used to represent the normal, medium and high states respectively. Should the faults at medium state are not detected on time, it may lead a more serious fault (high state). Thus, this technique is robust to identify a fault of an induction machine at the incipient state with a very minimal time.

Advanced model of IM including rotor slot harmonics

Purpose – The purpose of this paper is to present a detailed advanced dynamical model of induction machine (IM) with unskewed rotor bars, including rotor slot harmonics. Design/methodology/approach – Procedure of IM modeling using results from finite element analysis (FEA). Series of magneto-static FEA simulations are used to obtain matrix of IM inductances as a function of rotor angular position and geometry. Each element in this matrix is represented by Fourier series (FS) and incorporated in proposed dynamical model. Using or neglecting various elements in FS of inductance matrix may be useful for determining which component of the series has dominant influence on harmonic content of stator currents, torque ripple or speed variation. The usefulness of application of presented model is verified comparing with time-stepping FEA simulations. Findings – Although the model is not suitable for usage in on-line regulation of IM drives, but the results of simulations may be used to thoroughly explain origins of higher order harmonics in stator currents of IM and help improve sensorless speed estimation algorithms and fault diagnostics. Originality/value – This paper shows an approach to the modeling of IM which includes effects of non-uniform air gap and non-sinusoidal distributions of magneto-motive forces. Inductance matrix elements are complex functions of rotor position, geometry and winding distributions and it gives an opportunity for detail analysis of IM behavior in numerous applications.

Effects of the simultaneous presence of static eccentricity and broken rotor bars on the stator current of induction machine

Many papers are available in the literature about detection of faults in induction machines. However, they generally deal only with a single fault. Instead, in practice, the case of mixed faults is quite common: the simultaneous presence of broken rotor bars and an intrinsic eccentricity or a coupling misalignment occurs often in an induction machine. The aim of this paper is to analyze theoretically and experimentally the stator current of an induction machine operating with mixed faults: broken rotor bars and static eccentricity (SE). First, an analytical expression for the mutual inductances under SE is derived using a mixture of modified winding function and Fourier series approach. Then, both theoretical and simulation studies are presented to show how the stator current is influenced by the simultaneous presence of (SE) and broken rotor bars with the consideration of the speed ripple effect. It is demonstrated that, in addition to the well-known characteristic frequencies of broken bars, and the rotor slot harmonic (RSH) used for the detection of (SE), this kind of mixed fault introduces in the stator current a series of additional harmonics, in the form of sidebands centered around the fundamental and RSH. More important, it is shown that some of these harmonics are similar to the frequencies introduced by the mixed eccentricity. Finally, experimental results have been presented to validate the analytical and simulation results.