Diagnosis of Inter-Turn Short Circuit for a Polyphase Induction Motor in Closed-Loop Vector-Controlled Drives

The main objective of this paper is to develop and experimentally verify a new technique to detect an inter-turn short circuit in one phase of a stator winding of an induction motor energized from a vector-controlled drive. This is in order to overcome the fault masking difficulties associated with the concept of depending on the actual magnetic field pendulous oscillation between the conventional voltage and current space vectors with respect to a reference that is unaltered by the compensation action of the drive. This technique is based on the flux pendulous oscillation phenomenon. This flux pendulous oscillation is also described in this paper, this in addition to the magnetic field pendulous oscillation previously addressed in prior publications. The new approach has been verified through experimental results which are represented here

Fault-Tolerant Operation of Delta-Connected Scalar- and Vector-Controlled AC Motor Drives

Operation and analysis of delta-connected ac motor-drive systems under fault-tolerant open-phase mode of operation is introduced in this paper for both scalar- and vector-controlled motor-drive systems. This technique enables the operation of the three-phase motor upon a failure in one of its phases without the need of a special fault-detection algorithm. It is mainly used to significantly mitigate torque pulsations, which are caused by an open-delta configuration in the stator windings. The performance of the fault-tolerant system was verified using a detailed time stepping finite element simulation as well experimental tests for a 5-hp 460-V induction motor-drive system and the results are presented in this paper This paper also compares the operation of this fault-tolerant mode of operation for the cases of scalar-controlled and closed-loop vector-controlled motor-drive systems

Fault-Tolerant Technique for Δ-Connected AC-Motor Drives

A fault-tolerant technique for motor-drive systems is introduced in this paper. The technique is merely presented for ac motors with Δ-connected circuits in their stator windings. In this technique, the faulty phase is isolated by solid-state switches after the occurrence of a failure in one of the stator phases. Then, the fault-tolerant technique manages current-flow in the remaining healthy phases. This technique is to significantly mitigate torque pulsations, which are caused by an open-Δ configuration in the stator windings. The performance of the fault-tolerant technique was experimentally verified using a 5-hp 460-V induction motor-drive system and the results are presented in this paper

Complications of Third Molar Extraction: A retrospective study from a tertiary healthcare centre in Oman

Objectives: This retrospective study aimed to investigate complications associated with the extraction of third molars at a tertiary healthcare centre in Oman. Methods: All consecutive patients who underwent extraction of one or more impacted third molars under general anaesthesia at Sultan Qaboos University Hospital, Muscat, Oman, between January 2007 and December 2017 were included. Age, gender, indication for extraction, teeth removed, procedure and complications were recorded. Results: A total of 1,116 third molars (56% mandibular and 44% maxillary) were extracted and the majority (67.7%) were from female patients. The mean age at extraction was 24 ± 5 years and most patients (77.7%) were 20‒29 years old. The intraoperative and postoperative complication rates were 3.7% and 8.3%, respectively. The intraoperative complications included tuberosity fracture (1.2%), root fracture (1.1%), bleeding (0.7%), soft tissue injury (0.5%) and adjacent tooth damage (0.2%). Postoperative complications were sensory nerve injuries (7.2%), swelling/pain/trismus (0.6%) and dry socket (0.5%). Nerve injury was temporary in 41 patients and permanent in four cases. A statistically significant relationship was observed between those aged 30‒39 years and dry socket (P = 0.010) as well as bone removal and all postoperative complications (P = 0.001). Conclusion: Most complications resulting from third molar extractions were minor and within the reported ranges in the scientific literature. However, increased age and bone removal were associated with a higher risk of complications. These findings may help to guide treatment planning, informed consent and patient education.Keywords: Third Molar; Tooth Extraction; Complications; Lingual Nerve; Inferior Alveolar Nerve; Oman

Pontine haemorrhage due to chondrosarcoma of the skull base

A young adult presented with acute weakness of right side of body and slurring of speech. An initial brain CT scan showed a pontine haemorrhage, however MRI done a few days later revealed a mass in the left parapharyngeal space. Histopathology of the mass revealed that it was a chondrosarcoma. Subsequently the patient was initially treated with chemotherapy and radiotherapy and later surgery. Skull base chondrosarcomabe is to be included in the differentials of a young patient presenting with signs consistent with pontine haemorrhage

Analysis and Diagnostics of Adjacent and Nonadjacent Broken-Rotor-Bar Faults in Squirrel-Cage Induction Machines

In this paper, faults associated with the rotor of an induction machine are considered. More specifically, effects of adjacent and nonadjacent bar breakages on rotor fault diagnostics in squirrel-cage induction machines are studied. It is shown that some nonadjacent bar breakages may result in the masking of the commonly used fault indices and, hence, may lead to a possible misdiagnosis of the machine. A discussion of the possible scenarios of these breakages as well as some conclusions regarding the types of squirrel-cage induction machines (number of poles, number of squirrel-cage bars, etc.) that may be more prone to these nonadjacent types of failures are presented. This discussion is supported through both simulation and experimental results. It is also shown that secondary fault effects can be used to diagnose such nonadjacent bar breakages

A Reconfigurable Motor for Experimental Emulation of Stator Winding Inter-Turn and Broken Bar Faults in Polyphase Induction Machines (Journal article)

The benefits and drawbacks of a 5-hp reconfigurable induction motor, which was designed for experimental emulation of stator winding interturn and broken rotor bar faults, are presented in this paper. It was perceived that this motor had the potential of quick and easy reconfiguration to produce the desired stator and rotor faults in a variety of different fault combinations. Hence, this motor was anticipated to make a useful test bed for evaluation of the efficacy of existing and new motor fault diagnostics techniques and not the study of insulation failure mechanisms. Accordingly, it was anticipated that this reconfigurable motor would eliminate the need to permanently destroy machine components such as stator windings or rotor bars when acquiring data from a faulty machine for fault diagnostic purposes. Experimental results under healthy and various faulty conditions are presented in this paper, including issues associated with rotor bar-end ring contact resistances that showed the drawbacks of this motor in so far as emulation of rotor bar breakages. However, emulation of stator-turn fault scenarios was successfully accomplished

Efficient removal of norfloxacin using nano zerovalent cerium composite biochar-catalyzed peroxydisulfate

Norfloxacin (NOR), an important antibiotic used for the treatment of different infections which is reportedly causing huge quantity of water pollution and severe environmental issues. In this study, biochar prepared from Phoenix dactylifera roots biomass (PB) and composited with mesoporous nano-zerovalent cerium (nZVCe) was used for treatment of NOR solutions. The various characterization and treatment studies showed successful formation of the nZVCe and PB composite. The nZVCe was found to improve physiological characteristics and catalytic efficiency of PB. The nZVCe/PB composite caused 52% removal of NOR as compared to 23% by the individual PB. The use of peroxydisulfate (PDS) with PB and nZVCe/PB showed further improvement in the removal of NOR and caused 58 and 84% removal efficiencies of NOR by PB/PDS and nZVCe/PB/PDS, respectively. The use of PDS with PB and nZVCe/PB was found to yield ●OH and SO4 ●– which improved degradation of NOR, however, addition of ●OH and SO4 ●– scavengers impeded NOR degradation. The PB was found to have several oxygen functional groups which decomposed PDS into ●OH and SO4 ●–. The nZVCe/PB showed high recovery, reusability, and stability and caused high removal of NOR even at fifth cycle of treatment both in the absence and presence of PDS. The treatment of NOR by nZVCe/PB-catalyzed PDS showed encouraging results under different pH, and varying concentrations of PDS, nZVCe/PB, and NOR as well as in real water samples which suggest potential practical applications of NOR contaminated water. Degradation of NOR resulted into several products and the resulting final product proved to be non-toxic

Effect of Nickel Content on the Corrosion Resistance of Iron-Nickel Alloys in Concentrated Hydrochloric Acid Pickling Solutions

The effect of Ni content on the resistance against corrosion of Fe-36% Ni and Fe-45% Ni alloys in 1 M hydrochloric acid pickling solution was reported. Various electrochemical and spectroscopic techniques such as potentiodynamic cyclic polarization (CPP), open-circuit potential (OCP), electrochemical impedance spectroscopy (EIS), potentiostatic current-time (PCT), and scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) have been employed. CPP measurements indicated that the corrosion current and corrosion rate recorded lower values for the alloy that had higher nickel content. OCP curves proved that the presence of high Ni content shifts the absolute potential to the positive potential direction. EIS results revealed that the surface and polarization resistances were much higher for the alloy with higher Ni content. PCT curves also showed that the absolute currents were lower for Fe-45% Ni alloy. All results were in good agreement with others and confirmed clearly that the corrosion resistance in HCl solutions for Fe-45% Ni alloy was higher than that obtained for Fe-45% Ni alloy