Investigating inter-turn fault in transformer using TTR and FRA

Transformers are one of the significant elements in the power system network. The Transformer function is to step up and down the voltages. When the transformer operating in high load, it exposes to failures. There are various transformer failures which could have a serious effect on the transformer efficiency. For example, winding deformation, tap changer damage, and short turns (inter-turn fault). The transformer inter-turns fault reduces the number of turns in the winding. To detect inter-turn fault, the transformer turn ratio test is the basic method used. On the other hand, frequency response analysis has been recognized to monitor the mechanical condition of the transformer winding. The frequency response analysis method can be conducted in four measurement connection. They are end to end open circuit test, end to end short circuit test, capacitive inter-winding, and inductive inter-winding. The inductive inter-winding low-frequency region is determined by the transformer turn ratio. This statement was mentioned in CIGRE A2.26. However, there are not approved studies on this issue. This study investigates the transformer inter-turn fault using transformer turn ratio test and frequency response analysis. In addition, this study performs various of statistical indicators on the FRA results. The statistical indicators are used to detect the variation between the normal and inter-turn fault responses. Also, this study proposes statistical indicators limits. After that compare the FRA and TTR results and check if the turn ratio results can be obtained using FRA inductive inter-winding test. Findings that FRA inductive inter-winding test can detect inter-turn fault. This can be determined by the absolute sum logarithmic error (ASLE), mean square error (MSE), and standard deviation (SD). Also, there are indicator limits has been proposed for ALSE and SD. This study finding helps to use the frequency response analysis method to replace the conventional turn ratio test

Mathematical and numerical study of the concentration effect of red cells in blood

International audienc

Modelling the evolution of cerebral aneurysms: biomechanics, mechanobiology and multiscale modelling

Intracranial aneurysms (IAs) are abnormal dilatations of the cerebral vasculature. Computational modelling may shed light on the aetiology of the disease and lead to improved criteria to assist diagnostic decisions. We briefly review models of aneurysm evolution to date and present a novel fluid-solid-growth (FSG) framework for patient-specific modelling of IA evolution. We illustrate its application to 4 clinical cases depicting an IA. The section of arterial geometry containing the IA is removed and replaced with a cylindrical section: this represents an idealised section of healthy artery upon which IA evolution is simulated. The utilisation of patient-specific geometries enables G&R to be explicitly linked to physiologically realistic spatial distributions and magnitudes of haemodynamic stimuli. In this study, we investigate the hypothesis that elastin degradation is driven by locally low wall shear stress (WSS). In 3 out of 4 cases, the evolved model IA geometry is qualitatively similar to the corresponding in vivo IA geometry. This suggests some tentative support for the hypothesis that low WSS plays a role in the mechanobiology of IA evolution

Evaluating Uncertainties in CFD Simulations of Patient-Specific Aorta Models using Grid Convergence Index Method

Cardiovascular diseases are among the most important causes of global mortality. Computational Fluid Dynamics (CFD) is a powerful research tool that analyzes the hemodynamics of artery and blood flow patterns. In this study, CFD simulations are performed to assess the patient-specific healthy aorta, fusiform, and saccular aneurysm with various mesh types, including tetrahedral, polyhedral, and poly-hexacore. The aim of this study is to explore how different mesh types and grid densities impact the hemodynamic properties of physiological flows, with the goal of identifying the most cost-effective meshing approach. A mesh independence study is carried out to ensure the precision of the results, considering the wall shear stress distribution. For this, five different mesh resolutions are generated for each geometry. The uncertainties of the simulations associated with the discretization techniques and solutions are evaluated using the Grid Convergence Index (GCI) method. The findings showed that increasing the mesh density provides smaller uncertainty. GCI values for the wall shear stress are in the range of convergence, indicating that the results are reliable and accurate. Mesh type selection affects the accuracy and computational cost of our simulations. The polyhedral and poly-hexacore meshes lead to a good compromise between precision and computational cost, while the tetrahedral mesh style gives the most precise results with fluctuation. This work provides a systematic approach based on the Grid Convergence Index method in order to select the most appropriate mesh type for evaluating uncertainties in CFD simulations of patient-specific healthy aortas and aortas with abdominal aneurysms. According to the findings and GCI analysis, the polyhedral mesh type was chosen for all patient-specific aorta models. The study clearly demonstrated its superiority over other mesh types, ...Comment: Research pape

Modeling of the aorta artery aneurysms and renal artery stenosis using cardiovascular electronic system

<p>Abstract</p> <p>Background</p> <p>The aortic aneurysm is a dilatation of the aortic wall which occurs in the saccular and fusiform types. The aortic aneurysms can rupture, if left untreated. The renal stenosis occurs when the flow of blood from the arteries leading to the kidneys is constricted by atherosclerotic plaque. This narrowing may lead to the renal failure. Previous works have shown that, modelling is a useful tool for understanding of cardiovascular system functioning and pathophysiology of the system. The present study is concerned with the modelling of aortic aneurysms and renal artery stenosis using the cardiovascular electronic system.</p> <p>Methods</p> <p>The geometrical models of the aortic aneurysms and renal artery stenosis, with different rates, were constructed based on the original anatomical data. The pressure drop of each section due to the aneurysms or stenosis was computed by means of computational fluid dynamics method. The compliance of each section with the aneurysms or stenosis is also calculated using the mathematical method. An electrical system representing the cardiovascular circulation was used to study the effects of these pressure drops and the compliance variations on this system.</p> <p>Results</p> <p>The results showed the decreasing of pressure along the aorta and renal arteries lengths, due to the aneurysms and stenosis, at the peak systole. The mathematical method demonstrated that compliances of the aorta sections and renal increased with the expansion rate of the aneurysms and stenosis. The results of the modelling, such as electrical pressure graphs, exhibited the features of the pathologies such as hypertension and were compared with the relevant experimental data.</p> <p>Conclusion</p> <p>We conclude from the study that the aortic aneurysms as well as renal artery stenosis may be the most important determinant of the arteries rupture and failure. Furthermore, these pathologies play important rules in increase of the cardiovascular pulse pressure which leads to the hypertension.</p

Empirical Validation of an In Silico Model Predicting the Fluid Dynamics of an Iliac Artery Aneurysm

Iliac artery aneurysms are considered rare and difficult to detect and treat. Prompt diagnosis and timely intervention are essential, because the incidence of rupture is as high as 50%. The reported mortality rate for patients who undergo surgery for ruptured iliac artery aneurysm ranges from 50% to 70%. This study developed an in-vitro mechanical model of an iliac artery aneurysm to verify the accuracy of computer simulation software. Both the in vitro model and the in silico model can be used for further research to develop better treatment technology. This study also looks at the different types of iliac artery aneurysms, risk factors that contribute to the development of an iliac artery aneurysms, and current treatment options

Sensitivity Analysis of Geometry Changes in the Simulation of Basilar Aneurysms

Computer simulation is a useful tool in the research and treatment of basilar aneurysms. Current technology allows researchers to create 3D models from cerebral vasculature in-vivo, allowing for the investigation of surgical options with minimal risk to the patient. The method used to construct these models overlooks smaller lateral arterial branches which are difficult to discern due to resolution limits of the imaging process. These lateral branches have minimal impact on the overall blood flow through the basilar artery, but they play a significant role in the health of the patient, so it is important to ensure sufficient blood will reach them after treatment is performed. In order to simulate the flow through the basilar artery and its branches, these smaller vessels must be added to the model manually. These lateral branches vary widely in size, location, and quantity between patients, but the resulting blood flow patterns through the basilar artery are relatively consistent. The purpose of this thesis is to gain a better understanding of how differences in the modeling of these lateral branches will affect the overall blood flow patterns both through the basilar artery and the branches themselves. The results of this investigation will help researchers to make more accurate models when simulating the flow through these lateral branches. The study was performed through a series of simulations in which the geometric variables in these branches: length, size, quantity, and location were altered and compared. A second set of simulations was performed to further investigate the use of a constant resistance as a replacement for artery length. The results of the study show that the flow resistance due to the length of an artery could be approximated using a constant pressure, but some wall length must be present in the model to avoid causing a flow disturbance. The location of the vessels did not appear to have a significant impact on the flow patterns. Increasing the number of arteries results in an overall increase in outlet area, which causes a reduction in blood velocity exiting the basilar artery. No other significant changes in the flow patterns were observed. Altering the size of the vessels had a similarly predictable change in flow distribution, with a greater increase in flow per area increase, which follows Poiseuille’s model for laminar flow through tubes. The results from the second series of simulations verified that modifying the static distal pressure at an artery could accurately replace adjusting the artery length. These studies showed the importance of accounting for the flow distribution, the recirculation regions, and the flow mixing when determining this distal outlet pressure

Fluid-structure interaction in abdominal aortic aneurysms: effects of asymmetry and wall thickness

BACKGROUND: Abdominal aortic aneurysm (AAA) is a prevalent disease which is of significant concern because of the morbidity associated with the continuing expansion of the abdominal aorta and its ultimate rupture. The transient interaction between blood flow and the wall contributes to wall stress which, if it exceeds the failure strength of the dilated arterial wall, will lead to aneurysm rupture. Utilizing a computational approach, the biomechanical environment of virtual AAAs can be evaluated to study the affects of asymmetry and wall thickness on this stress, two parameters that contribute to increased risk of aneurysm rupture. METHODS: Ten virtual aneurysm models were created with five different asymmetry parameters ranging from β = 0.2 to 1.0 and either a uniform or variable wall thickness to study the flow and wall dynamics by means of fully coupled fluid-structure interaction (FSI) analyses. The AAA wall was designed to have a (i) uniform 1.5 mm thickness or (ii) variable thickness ranging from 0.5 – 1.5 mm extruded normally from the boundary surface of the lumen. These models were meshed with linear hexahedral elements, imported into a commercial finite element code and analyzed under transient flow conditions. The method proposed was then compared with traditional computational solid stress techniques on the basis of peak wall stress predictions and cost of computational effort. RESULTS: The results provide quantitative predictions of flow patterns and wall mechanics as well as the effects of aneurysm asymmetry and wall thickness heterogeneity on the estimation of peak wall stress. These parameters affect the magnitude and distribution of Von Mises stresses; varying wall thickness increases the maximum Von Mises stress by 4 times its uniform thickness counterpart. A pre-peak systole retrograde flow was observed in the AAA sac for all models, which is due to the elastic energy stored in the compliant arterial wall and the expansion force of the artery during systole. CONCLUSION: Both wall thickness and geometry asymmetry affect the stress exhibited by a virtual AAA. Our results suggest that an asymmetric AAA with regional variations in wall thickness would be exposed to higher mechanical stresses and an increased risk of rupture than a more fusiform AAA with uniform wall thickness. Therefore, it is important to accurately reproduce vessel geometry and wall thickness in computational predictions of AAA biomechanics