A wavelet-based technique to detect stator faults in inverter-fed induction motors

This paper proposes a novel method to overcome one of the difficulties arising from the VSI supply of low voltage motors in the early detection of inter-turns stator short circuits, i.e. the presence of a high variability of harmonics both in the stator current and in the external stray flux. A pre-processing technique based on the wavelet decomposition has experimentally proved to be able to remove this variability and therefore to make more robust the diagnostics of this fault and its progression by means of the spectral analysis of each of the measured signals (current of one phase and stray flux measured with two different sensors)

Linear Discriminant Analysis for an Automatic Detection of Stator Faults in Induction Motor Drives

This paper presents a method for an automatic detection of a stator short circuit and for the estimation of its severity in inverter-fed induction motors, in different conditions of speed and load. The method is based on the Linear Discriminant Analysis and on the spectral analysis of three signals (current of one phase and external stray flux measured with two different sensors). In order to obtain a relatively simple instrument for applications in industrial cases, only the first odd harmonics multiple of the fundamental have been chosen as features for the classifiers. All the considered signals have provided interesting diagnostic results, even if the best performance is given by the current

An Experimental Investigation of the High Frequency Effects in Low Voltage Electrical Drives

This paper presents the results of an experimental investigation on the harmful effects due to the PWM inverter supply on low voltage induction motors. Laboratory tests have verified on two different models of motors the reflected wave phenomenon, which induces on their terminals a rising voltage edge with peaks higher than twice the DC link voltage; further tests in a qualified firm have revealed that these peaks exceed the partial discharge inception voltage (PDIV) for one of the two types of motor. An invasive and specialized series of tests on the insulation material extracted from the stators has proven that an appropriate insulation system represents the best solution to avoid an early die-off of inverter-fed motors. Other two mitigation methods proposed in the literature have been experimentally tested, revealing that they do not assure the solution to the problem

Are all cases of paediatric essential thrombocythaemia really myeloproliferative neoplasms? Analysis of a large cohort

Sporadic essential thrombocythaemia (ET) is rare in paediatrics, and the diagnostic and clinical approach to paediatric cases cannot be simply copied from experience with adults. Here, we assessed 89 children with a clinical diagnosis of ET and found that 23 patients (258%) had a clonal disease. The JAK2 V617F mutation was identified in 14 children, 1 child had the MPL W515L mutation, and 6 had CALR mutations. The monoclonal X-chromosome inactivation pattern was seen in six patients (two with JAK2 V617F and two with CALR mutations). The other 66 patients (742%) had persistent thrombocytosis with no clonality. There were no clinical or haematological differences between the clonal and non-clonal patients. The relative proportion of ET-specific mutations in the clonal children was much the same as in adults. The higher prevalence of nonclonal cases suggests that some patients may not have myeloproliferative neoplasms, with significant implications for their treatment