A qualified dry-type transformer under the combined seismic conditions

This article presents the design, seismic simulation, and seismic testing of a 2500 kVA 36 kV 7.7-ton dry-type transformer designed to withstand the rigorous IEEE693-2018 moderate-level seismic test involving dynamic forces in the range of 0-55 Hz and 0.5 g acceleration. The testing was conducted at IAGB Test Company in Munich, Germany, and we are pleased to report that the test was successfully completed. Remarkably, the transformer design eliminates the need for additional consoles or supports, achieving stability solely through the use of eight M24 fasteners for secure grounding. This innovative approach ensures the transformer’s resilience under seismic conditions, addressing critical considerations for power infrastructure in earthquake-prone regions. The results and implications of this seismic testing contribute valuable insights to the field of transformer design and seismic resilience

Development of transformers with natural ester and cellulose or aramid insulation

This study describes selected research studies performed for developing design rules for power transformers using natural esters. The presented simulation results verified adequacy of design rules and allowed for adjustments needed for implementing the new insulation system vs. the one based on mineral oil and cellulose-based solid insulation. They were also used as a base for the next transformer design combining natural ester with aramid insulation

CFD study of the impact of the deviation on the mass flow inlet on winding hot-spot temperature of a power transformer using mineral and ester oils

This work presents a study where a deviation on the mass flow rate in adjacent sectors of the winding is considered. A CFD model was developed for this study, where heat transfer between sectors is enabled due to the lack of thermal symmetry, and the goal of this study is to determine whether this effect can be neglected or not. To carry out this study, a Low Voltage Winding of a 100 MVA power transformer was selected. This transformer has been manufactured and tested by BEST Transformers, and the results obtained from the heat run test were used to validate the CFD model. The study also considered an alternative dielectric liquid, natural ester, in order to estimate if the different thermal and hydraulic conditions can affect to the relevance of the studied effect. The CFD simulations have been carried out with ANSYS Fluent. The results showed a deviation of 3-4% of the heat dissipated due to the non-symmetric conditions with a 10% of mass flow deviation, which is the heat transfer between the adjacent sectors. This effect is identical when considering mineral oil or natural ester. The results shows there is a small impact of the winding temperatures due to this effect, and that it can be considered negligible.Part of the work was performed during secondments between BEST Transformers and the University of Cantabria executed in the framework of the BIOTRAFO project “Raising knowledge and developing technology for the design and deployment of high-performance power transformers immersed in biodegradable fluids”, H2020-MSCA-RISE2018- 823969, 2019-21. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 823969. Also, we acknowledge the support of the Spanish Ministry of Science and Innovation by means of the National Research Project Asset management of biodegradable-fluid-based transformers (PID2019-107126RB-C22/AEI/ 10.13039/501100011033

Use of alternative fluids in very high-power transformers: experimental and numerical thermal studies

The very high-power transformer lifespan depends mainly on the temperature that cellulose insulation reaches during its operation. Traditionally, its cooling has been carried out using mineral oil as coolant. Nowadays, alternative ester-based liquids are under study as substitutes due to their better environmental and re-safety properties. This paper compares the cooling capacity of two ester-based uids with that of a mineral oil using a 3D numerical model of a 100 MVA low voltage winding of a power transformer with axial cooling system and ONAN cooling mode. Heat-run test results with mineral oil have been used to validate this model. As a rst approximation, according to the comparison developed, esterbased uids could replace mineral oils in this type of transformers when they are going to work in a range of powers close to the rated one.This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 823969. Also, we acknowledge the support of the Spanish Ministry of Science and Innovation by means of the National Research Project "Asset management of biodegradable-fluid-based transformers'' (PID2019-107126RB-C22) and the Universities and Research Council of the Government of Cantabria by means of the grant "Biodegradable fluids in electrical power transformers: solid dielectric impregnation and thermal modeling with THNM'', VP32, 2019-2

Performance analysis of natural, synthetic and mineral oil in a 100 MVA power transformer

The power transformer lifespan depends on the dielectric capacity of its insulation system, mainly of the paper. Integrity of this material depends significantly on the cooling capacity of the oil used to cool it. Currently, ester-based fluids are being researched with the intention to substitute the traditional cooling liquid in power transformers, the mineral oil. Here, cooling capacity of two different ester-based fluids, a synthetic and anatural esters, is compared with that of a mineral oil. To carry out this task, CFD results of a low voltage winding of a 100 MVA power transformer jointly with the experimental ones get from a heat-run test done in this transformer are used. This winding has an axial cooling system in ON regime. As a result of this study, it can be inferred that alternative liquids could be used with high load levels (rated power or higher) since no significant changes in the temperatures distribution of the winding cooled with these fluids in comparison with that get with mineral oil are appreciated.The authors of this research wish to thank for its financial support: - The European Union by means of the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 823969. This grant fund the European project Biotrafo: raising knowledge and developing technology for the design and deployment of high performance power transformers immersed in biodegradable fluids; European Commission, h2020-mscarise-2018- 823969; 2019-21 - The Spanish Ministry of Science, Innovation and Universities by means of the National Research Project Improvement of Insulation Systems of Transformers through Dielectric Nanofluids (DPI2015-71219-C2-1- R). - The Universities and Reseach Council of the Government of Cantabria by means of the grant Fluidos biodegradables en transformadores eléctricos de potencia: impregnación de dieléctricos sólidos y modelado térmico con THNM, VP32, 2019-2

Renal complications of lipodystrophy: A closer look at the natural history of kidney disease

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/144612/1/cen13732_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/144612/2/cen13732.pd

On Cesàro summability of vector valued multiplier spaces and operator valued series

In this paper, we introduce and study vector valued multiplier spaces with the help of the sequence of continuous linear operators between normed spaces and Cesàro convergence. Also, we obtain a new version of the Orlicz–Pettis Theorem by means of Cesàro summability

Weakly unconditionally Cauchy series and Fibonacci sequence spaces

We study new sequence spaces associated to sequences in normed spaces and the band matrix F̂ defined by the Fibonacci sequence. We give some characterizations of continuous linear operators and weakly unconditionally Cauchy series by means of completeness of the new sequence spaces. Also, we characterize the barreledness of a normed space via weakly∗ unconditionally Cauchy series in X*

Investigation of magnetic wall shunt combinations on 650 MVA power transformers by finite element methods

Power transformer losses mainly include open circuit loss and short circuit loss. Open circuit loss is created in the iron core of the transformer. Short circuit loss, copper loss, and stray loss are known collectively as “short circuit loss”. Copper loss is created in windings: current flows through the DC resistance in windings. Stray loss is caused by eddy currents in high magnetic permeability and high conductivity of components such as tanks, windings, and structural parts. This is why the volume limit of power transformers and the ratio of stray loss in structural parts and the tank cannot be ignored. This has led transformer manufacturers to add magnetic wall shunts to reduce stray loss. But often, too many magnetic wall shunts are added or misplaced, which results in increased cost and reduced performance. By improving stray loss distribution in power transformers, magnetic wall shunt design can be optimized, and the tradeoff of cost and performance can be balanced

Retrospective analysis of factors affecting sperm retrieval with microscopic testicular sperm extraction in infertile men with Klinefelter syndrome: A multicentre study

The aim of this study was to evaluate the data currently available on predictors of sperm retrieval (SR) in infertile men with Klinefelter syndrome (KS). The data of infertile patients with KS who were evaluated for primary infertility in the andrology outpatient clinics of six centres were retrospectively reviewed. SR, fertilization and pregnancy rates were evaluated. While SR was achieved with microscopic testicular sperm extraction (mTESE) in 57.7% of the cases, the positive pregnancy rate was 22%. While mosaicism was significantly associated with achieving pregnancy, it was not significant for SR (p = 0.002 and p = 0.136 respectively). However, receiving medical treatment prior to mTESE was a positive factor for both achieving pregnancy (p = 0.010) and successful SR (p = 0.032). Unsurprisingly, fertilization rate was a variable that increased the pregnancy rate (p = 0.001). In addition, total testosterone value correlated with SR (p < 0.001). For patients with KS, pregnancy can be achieved by obtaining sperm through mTESE, especially in those with mosaic karyotype, normal partner fertility, a high fertilization rate and who receive appropriate medical treatment before mTESE