Characterization of transformer FRA signature under various winding faults

Frequency response analysis (FRA) is gaining global popularity in detecting power transformer winding and core deformations due to the development of FRA test equipment. However, because FRA relies on graphical analysis, interpretation of its signatures is still a very specialized area that calls for skillful personnel to detect the sort and likely place of the fault as so far, there is no reliable standard code for FRA signature classification and quantification. This paper aims to initiate the establishment of standard codes for FRA signature interpretation through comprehensive simulation analysis on a detailed transformer distributed parameters-based model. Various mechanical faults such as axial displacement, buckling stress, disk space variation and bushing fault are simulated on the model to study its impact on the FRA signature. The main contribution of this paper is the comprehensive table it presents for FRA signature sensitivity to winding and core deformations that can be used for classification and quantification of the transformer FRA signature

Hepatoprotective effects of silymarin on liver injury via irisin upregulation and oxidative stress reduction in rats with type 2 diabetes

Background: Diabetes is one of the most prevalent metabolic diseases. Irisin (FNDC5 protein) is involved in the new strategy of combating type 2 diabetes. In the liver, the antidiabetic mechanism of silymarin at the molecular level is unknown. This study investigated the effects of silymarin on irisin and the related gene expression and oxidative stress status in the liver of type 2 diabetic rats. Methods: Thirty-six rats were divided into 6 groups (n=6 each) by simple randomization: control, control+silymarin (60 mg/kg daily in normal saline orally for 60 days), control+silymarin (120 mg/kg daily in normal saline orally for 60 days), diabetic, diabetic+silymarin (60 mg/kg daily for 60 days), and diabetic+silymarin (120 mg/kg daily for 60 days). Biochemical parameters were measured by spectrophotometric and immunoassay methods, and quantitative polymerase chain reaction was used to evaluate gene expression. The data were analyzed by one-way ANOVA, followed by the Tukey test, using SPSS software, version 16.0. The results were considered statistically significant at a P value less than 0.05. Results: In the diabetic rats treated with silymarin (60 and 120 mg/kg), by comparison with the diabetic group, body weight (P=0.04 and P=0.02), insulin (P<0.001), expression of PGC-1α (P=0.04 and P=0.02), expression of FNDC5 (P=0.03 and P=0.01), and concentration of irisin in the liver (P=0.02 and P=0.01) and serum (P<0.001) were significantly increased, whereas the levels of glucose (P<0.001), HOMA-IR (P=0.03 and P=0.01), and liver injury markers (P<0.001) were significantly reduced. Oxidative stress status and histopathological changes were improved in the treated groups. Conclusion: These results suggest that silymarin because of its ability to upregulate irisin and antioxidant effects can be considered an antidiabetic agent. © 2019, Shiraz University of Medical Sciences. All rights reserved

Structure-Sensitive Mechanism of Nanographene Failure

The response of a nanographene sheet to external stresses is considered in terms of a mechanochemical reaction. The quantum chemical realization of the approach is based on a coordinate-of-reaction concept for the purpose of introducing a mechanochemical internal coordinate (MIC) that specifies a deformational mode. The related force of response is calculated as the energy gradient along the MIC, while the atomic configuration is optimized over all of the other coordinates under the MIC constant-pitch elongation. The approach is applied to the benzene molecule and (5, 5) nanographene. A drastic anisotropy in the microscopic behavior of both objects under elongation along a MIC has been observed when the MIC is oriented either along or normally to the C-C bonds chain. Both the anisotropy and high stiffness of the nanographene originate at the response of the benzenoid unit to stress.Comment: 19 pages, 7 figures 1 tabl

Application of S transform for detection of external interferences in online transformer impulse frequency response analysis

Online impulse frequency response analysis is a recently-developed diagnostic method for in service transformer with a promising outlook. This paper aims to detect the impact of external interferences including pulse shaped interferences from switching operations and other phenomena in the power system on the frequency response of the transformer. For modeling the transformer for online IFRA, a simulation approach based on finite element analysis (FEA) and circuit analysis is used. In this approach, instead of using a linear model with static parameters, 3D finite element model of the transformer is calculated in Maxwell Software and then exported into an external Maxwell Spice circuit which allows for study the terminal behaviors of the transformer. A modified S transform is then applied to the recorded input and output signals in healthy and faulty conditions to construct the electrical impedance as well as the time-frequency contours of the transient responses

Condition assessment of power transformer bushing using SFRA and DGA as auxiliary tools

Dielectric insulation of a transformer bushing deteriorates as a function of temperature, oxidation, and moisture. This causes accelerated aging of oil and cellulosic solid insulation, generating fault gases within bushing oil and eventual permanent failure. To prevent such failures, effective analyses and diagnoses need to be investigated. Dissolved Gas Analysis (DGA) can give the indication of internal abnormalities inside the transformer bushing. In addition, Frequency response analysis (FRA) is a widely accepted tool for mechanical deformation diagnosis within power transformers. Although a large number of studies have been conducted on the detection of transformer winding deformation by FRA technique, the impact of bushing faults on the transformer FRA signature has not been sufficiently investigated. It is the goal of this paper to propose precise simulation as well as practical analyses demonstrating the impact of bushing faults on the FRA signature. A real transformer bushing geometry is modelled through 3D finite element analysis (FEM) on which different bushing faults are emulated. To verify the derived simulation results, DGA of transformer oil as well as FRA are performed on a three-phase, 132 kV, 315 MVA power transformer. It can be observed clearly from the results, that bushing faults have an impact on the FRA signature and DGA of the power transformer

Online detection of partial discharge inside power transformer winding through IFRA

© 2017 IEEE. Predictive maintenance offers substantial benefits for detecting the early signs of power transformer faults before they burgeon into catastrophic failures. Online impulse frequency response analysis is a recently-developed diagnostic method for in service transformer with a promising outlook. This paper aims to propose an online partial discharge detection method the online IFRA test. To emulate the dynamic performance characteristics of in service transformer, 3D finite element model of the transformer is calculated in Maxwell Software. In post processing, the FEM sub-circuit model is exported into an external Maxwell Spice circuit to study the terminal behaviors of the transformer. A pulse signal simulating PD is injected between sections of the LV winding. The S transform is then applied to the recorded input and output signals in healthy and faulty conditions to construct the electrical impedance as well as the time-frequency contours of the transient responses. Also, a mechanical deformation is imposed on the transformer to compare its impact on online IFRA to the impact of internal partial discharge

Application of online impulse technique to diagnose inter-turn short circuit in transformer windings

Inter-turn short circuit fault is a significant problem in power transformers which if not detected at early stages, can propagate in power networks and eventually burgeon into catastrophic faults and substantial costs. Online frequency response analysis (FRA) is well on its way of becoming a reliable tool for condition monitoring and fault detection of transformer since no disconnection is required to conduct the test. Among the two existing FRA methods, sweep frequency response analysis (SFRA) and impulse frequency response analysis (IFRA), IFRA has reached the potential for online application. This contribution aims to detect interturn short circuit fault through online transfer function monitoring of the power transformer winding using the impulse technique, a method which utilizes a capacitive coupling circuit to inject a controlled high voltage nanosecond pulse into the transformer winding. To this end, 3D finite element electromagnetic analysis and transformer equivalent high frequency electrical model have been used as auxiliary tools to precisely emulate the real transformer operation and investigate the impact of inter-turn short-circuit faults on the transformer equivalent circuit parameters and thereby, transformer online FRA signature. Simulations were performed with two different levels of interturn fault severity. The results show that inter-turn short circuit can be effectively detected with the transformer in service using the impulse method