Detection of Power Transformer Bushing Faults and Oil Degradation using Frequency Response Analysis

Frequency response analysis (FRA) has been globally accepted as a reliable tool to detect mechanical deformation within power transformers. However, because of its reliance on graphical analysis, interpretation of FRA signature is still a challenging area that calls for skilled personnel, as so far, there is no widely accepted reliable standard code for FRA signature identification and quantification. While several papers investigating the impact of various mechanical winding deformations on the transformer FRA signature can be found in the literature, no attention was given to investigate the impact of various bushing faults and transformer oil degradation on the FRA signature. This paper introduces a detailed simulation and practical analyses to elaborate the impact of bushing faults as well as transformer oil degradation on the transformer FRA signature. In this regard, the physical geometrical dimension of a three phase power transformer is simulated using 3D finite element analysis to emulate the real transformer operation. Various bushing faults have been emulated on the studied model and oil degradation is implemented through changing oil permittivity. Practical FRA test is conducted on a three phase 132kV, 35MVA power transformer to validate the simulation results. Results show that bushing faults and oil degradation can be visibly detected through FRA signature

Characterization of Power Transformer Frequency Response Signature using Finite Element Analysis

Power transformers are a vital link in electrical transmission and distribution networks. Monitoring and diagnostic techniques are essential to decrease maintenance and improve the reliability of the equipment.This research has developed a novel, versatile, reliable and robust technique for modelling high frequency power transformers. The purpose of this modelling is to enable engineers to conduct sensitivity analyses of FRA in the course of evaluating mechanical defects of power transformer windings. The importance of this new development is that it can be applied successfully to industry transformers of real geometries

Protection of High-Voltage Transformer Bushings and Other Brittle Structures Against Impact

This dissertation contributes unique approaches to improve the fundamental understanding of the impact behavior of porcelain high-voltage (HV) transformer bushings under high-velocity impact, with a focus on their protection with feasible methods which could be quickly applied in service to prevent vandalism and other undesirable impact situations. The bushings are brittle and pressurized; prone to explosive damage when hit by a high-velocity projectile. Damaged bushings can destroy transformers and entire substations in complex fashions. This can put the power grid at risk for cascading failures and electrical blackouts, affecting consumers. Therefore, suggesting practical approaches which could be used to protect the bushings against impact is of paramount importance. Testing of impact protection concepts on a full-scale bushing without exploratory study is expensive. Therefore, this research focused heavily on the development of new laboratory based experimental and numerical approaches for pressurized borosilicate glass cylinders and flat plates using both ballistic and low-velocity impact techniques, to best represent a bushing under high-velocity impact. The laboratory-based testing approaches were further verified by full-scale impact tests with a .308 caliber Winchester rifle cartridge. It was discovered from the laboratory and full-scale tests that an unprotected bushing would display an explosive symmetrical distribution of fragments, potentially destroying transformers, other neighboring equipment, and personnel. It was also demonstrated for the first time that a protective elastomeric coating can be used on the surface of a bushing to absorb an explosive blast from a combined effect of high-velocity impact and internal pressure. Nature was used as a guide to select an appropriate polymer coating for blast mitigation. It turned out that small amounts of Line-X XS-100 applied on the surface of the cylinders, plates, and bushings dramatically changed their failure modes from brittle to ductile. Most importantly, Line-X XS-100 successfully confined fragments on pressurized borosilicate cylinders and full-scale transformer bushings. This research successfully used an extensive combination of engineering and scientific approaches to recommend a solution to a potentially serious engineering problem created by an explosion of an unprotected bushing in the middle of a HV substation

Designing and Modeling a Fail-Safe Mechanism to Be Used in Attachment of a Transcutaneous Femoral Implant to a Prosthetic Device

Amputations are quite common and even modern prosthetic devices are plagued by problems. There are approximately 2 million people living with limb loss in the U.S. and on average 185,000 amputations occur yearly. Common attachment mechanisms for external prosthetic components to a residual limb, that is, sockets, pose numerous challenges. Issues include skin irritation, discomfort, socket fit issues, and immobility. Issues include skin irritation, discomfort, socket fit issues, and immobility. Transcutaneous implants have great potential as a connection method for external prosthetic components to a residual limb but because the implants are typically solid, they correlate to extremely high infection rates at the skin interface. Only one such system is FDA-approved but is inadequate due to its corresponding high infection rates and suboptimal fail-safe mechanism. Highly porous transcutaneous technology potentially offers a solution to this problem via providing a permanent mounting point that bridges the skin and soft tissues while being anchored in the bone. However, a porous metal transcutaneous implant cannot be properly employed until a highly effective safety mechanism is engineered that prevents damage to the residual bone of the user when accidental loads are applied. Existing products on the market lack optimized fail-safe devices. A fail-safe mechanism is essential to release the prosthesis in both falls and more extreme circumstances, such as the device becoming caught, to prevent injury to the prosthetic device and the user’s residual skeleton and surrounding tissues. Hence, the present work, including manual calculations, finite element analysis, and mechanical testing, was undertaken to develop an optimized fail-safe mechanism to be incorporated into a porous metal transcutaneous implant system

Perspectives on energy security and renewable energies in Sub-Saharan Africa - Practical opportunities and regulatory challenges

Second Revised and Expanded Editio

The Republican Journal: Vol. 85, No. 1 - January 02,1913

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