Search

Copyright of Przegląd Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper proposes an operation modal analysis (OMA)-based approach to obtain a transformer's mechanical condition from vibrations during the transformer's transient processes, such as short-circuit and power-off conditions. Such processes generate a short transient vibration response, which yields a spectrum with poor frequency resolution. Vibration before the transient process could be included to increase the signal length; however, this would introduce a forced vibration component into the spectrum, making it challenging to distinguish the modal frequencies. To overcome these problems, a time–frequency analysis-based algorithm is proposed to extract the modal frequency spectrum from the vibration signal with the high-frequency resolution, providing clearer insight into the mechanical condition of the transformer. A faulty-state indicator is then proposed based on the similarity between the extracted modal spectrum and the initial modal spectrum obtained under a healthy state. To validate the proposed method, laboratory experiments were conducted under short-circuit and power-off conditions. Two mechanical faults—the looseness of the winding clamping and winding deformation—are introduced. The results show that both faults will cause variations in the modal frequency spectrum, leading to significant decreases in the indicator value. In summary, the proposed method can effectively evaluate a transformer's mechanical condition in an OMA setting. [ABSTRACT FROM AUTHOR]

Eddy current effects, which include skin and proximity effects, are usually associated only with frequency, but they are also affected by temperature. This paper analyzes the effect of both, temperature and frequency on skin and proximity effects in transformer windings. When analyzing transformer windings, despite the existence of powerful finite element analysis (FEA) modules, they return the total contribution of eddy current effects and do not separate the contributions of skin and proximity effects. This paper proposes an analytical method to determine the contribution of both effects to the AC winding resistance and leakage inductance based on the orthogonality of the skin and proximity effects. This method is based on the exact solution of the skin effect for an isolated round conductor combined with Dowell's solution of the proximity effect. Presented experimental results and FEA simulations based on a single-phase transformer have determined the accuracy of the proposed method, which allows accurate prediction of the temperature and frequency behavior of the winding resistance and leakage inductance.

The article presents theoretical and practical aspects of improving the designs of existing separation subsystems using the results of historical and patent information studies used to detect and extract ferromagnetic bodies in a flow of multicomponent non-magnetic lumpy, granular and finely divided and friable media. A new energysaving technological approach proposed with the effect of synchronously improving the performance of the transport and technological system and reducing the cost and energy costs during its operation, in particular in the material flow separation subsystem. A subsystem for the separation-detection of metal fragments in a non-magnetic granular medium proposed for the development of signaling and current control devices in extracting windings. To increase the extraction capacity during the purification of non-magnetic granular media, a design of a combined iron separator proposed. Mathematical modeling of the operation of the electromagnetic system of the combined iron separator of the transport system is carried out, on the basis of which a mathematical model of the magnetic field in its working area is proposed, which makes it possible to determine the extracting force from the windings with and current. An experimental verification of the results of theoretical studies of pulsed magnetic extraction of ferromagnetic bodies from a granular medium is carried out.

The choice of material, manufacturing process, and molding tool significantly affects the quality, environmental impact, and cost efficiency of composite components. Producing one-piece hollow profiles with smooth inner surfaces and undercuts presents major challenges for conventional mold concepts. There is yet no thorough review of shape-variable mandrels in composite manufacturing to be found in the literature. This paper provides an overview of research on shape memory polymers and other shape-variable materials used in tooling applications for composite manufacturing. This work covers shape memory, heat shrink, and other deformable tooling concepts that enable the production of one-piece Type V pressure vessels, air intake ducts, or curved struts and tubes. A systematic literature review in combination with a state-of-the-art open-source active learning tool ASReview is conducted. Fifteen relevant studies were identified. Research on shape-variable tooling is mainly conducted by three research groups in the USA and the PRC. The tooling is mostly made of unreinforced thermosets, especially styrene-based ones. Thermoplastic resins are less common, and reinforcements limit the usable elongation in the temporary shape. The shape variability is either a shape memory and/or a softening process, which, in all studies, is activated by heating. Release agents are widely used to ease demolding. No ecological or economical assessment of the manufacturing methods was conducted in the reviewed studies. Three fields for further research that could be identified are as follows: (1) thorough ecological end economical assessment of shape-variable mandrels in comparison with conventional tooling; (2) thermoplastic shape memory polymer mandrels; and (3) further investigation of simulation capabilities for shape memory mandrels. [ABSTRACT FROM AUTHOR]

Copyright of e & i Elektrotechnik und Informationstechnik is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Temperature distribution is an important index that reflects the safe operation ability of power transformers. In this paper, finite element simulation is used to study the magnetic field, loss, and temperature distribution of an ultra-high voltage converter transformer. Firstly, the magnetic reluctance equivalent method was proposed to establish a 2D axisymmetric model, and the frequency domain solution was achieved based on the magnetic energy equivalent method. The results demonstrate that this method reduces solving time by 10 times compared to traditional method, and the simulation results are consistent with measured short-circuit impedance, indicating the effectiveness and efficiency of this method. Secondly, the magnetic flux, loss, and temperature distribution of the winding were studied. It was found that eddy currents have a significant impact on the losses at the end and outer diameter of the winding, leading to uneven winding temperature distribution. The hot spot temperature with eddy current loss is 14.3 K higher than that without eddy current loss, and the hot spot temperature is 27.8 K higher than the average temperature, which is significantly different from AC transformers. This study has positive significance for the safe and reliable operation of converter transformers. [ABSTRACT FROM AUTHOR]

Copyright of Przegląd Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

When partial discharge occurs within transformers， the pulse current signal propagates along the winding. Detecting this pulse current signal at both ends of the winding enables the identification of partial discharge within the transformer. To this end， a wideband equivalent circuit model for the transformer is established. In high-voltage windings where partial discharges are likely to occur， partial discharge pulses are applied between different wound disks and the ground to simulate the discharge to the ground at different locations of the high-voltage winding. Pulse current signals are then collected at the end screen of the high-voltage casing and at the neutral point to study the propagation rules of the partial discharge pulse current signal at different locations within the transformer windings. Through calculations， it is observed that the energy ratios of pulse current signals in two distinct frequency bands are linearly correlated with the distance ratio of pulse current propagation， and the maximum error observed in this context is 9.80 wound disks. This method facilitates localization of partial discharge within the transformer， and the results of field experiment subsequently validate the effectiveness of this localization technique.

Conductor on round core (CORC) cables are superconductor rare earth-barium-copper-oxide (REBCO) based conductors that allow for high operating currents and have been becoming one of the most flexible high temperature superconducting (HTS) conductors to date. Nevertheless, due to the brittle nature of superconductor REBCO ceramics, the critical current exhibits a sensitive strain dependence, i.e., the critical current varies closely with strain, and especially raises a significant degradation once the strain exceeds a critical value. And, due to the complex deformation of tape winding and after cable stranding, firstly there is a practical challenge that how to accurately estimate the axial strain of the superconductor tape of cables under various deformations. In this paper, we developed the analytical models that can be used to accurately calculate the axial strain of the superconductor tape of CORC cables under the practical conditions of tape winding on the cable core, the cable bending, and twist deformations for stranding. The analytic model was validated by comparing the analytic result both with FEM numerical result and experimental data that the critical current of the superconducting tape varies with the core diameter of CORC cables. Further, on the analytic models, the axial strain, and the dependence on the core diameter and winding angle, the bending diameter, and the strand pitch were obtained respectively for CORC cables under tape winding, cable bending, and twist deformations. Particularly, the critical parameters, which are here defined at which the axial strain of the superconductor layer just reaches the critical strain, such as the critical core diameter, critical bending diameter, and critical pitch were determined. Thus, the analytic study of the strain of the superconductor REBCO tape of CORC cables will be helpful for CORC cables processing and further the design of high-level superconducting coils and magnets. [ABSTRACT FROM AUTHOR]

In this paper, a hermetically sealed transformer with a power of 1600 kVA is used to make the mechanical calculations and analysed according to the heat generated by energy transmission. The heat generated on the transformer causes the insulation oil to heat up and increase in volume. Accordingly, the increasing insulation oil volume in the transformer tank causes a pressure increase on the tank. In our study, mechanical stresses created by the temperature and pressure increase due to the heat generated are calculated. These calculations are investigated according to strength, cooling, and construction approaches of tank with the corrugated wall and analysed its effect in design using ANSYS@FLUENT and ANSYS@MECHANICAL combination simulation software based on Finite Element Method. Temperature distribution and thermal limitations are critical to correct design. Temperatures exceeding the permissible thermal limits can cause serious damage to transformer components. On the other hand, a tested prototype tank is provided to compare the numerical, analytical, and experimental values. However according to the results, the stress concentrations are observed at the critical connection points, indicating the possibility of failure if an extra unexpected load is real. [ABSTRACT FROM AUTHOR]

Copyright of BHM Berg- und Hüttenmännische Monatshefte is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Zhejiang Electric Power is the property of Zhejiang Electric Power Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper conducted an experimental study of reduced models of a main gas pipeline for avalanche damage considering operational conditions. Two options were considered as a method of avalanche damage prevention: single steel rings at the crack edges and steel winding with a winding pitch of 0.25 m. For the tension force, 5% of the steel wire breaking force was taken, which was equal to 1 mm. The ambient environment was simulated by a climatic chamber, where two options of temperature loads were considered: +20 °C and −10 °C. It was found that reinforcement with single rings of pipeline models under conditions of positive (+20 °C) and negative (−10 °C) temperatures showed that the crack opening width in the ring direction decreased 1.63 times and 1.9 times, accordingly. The crack length (longitudinal direction) decreased 2.18 times and 2.45 times, accordingly. The reinforcement of the pipeline models with prestressed wire winding on the crack propagation under conditions of positive (+20 °C) and negative (−10 °C) temperatures showed that the width of the crack opening in the ring direction decreased 1.5 times and 1.46 times, accordingly. The crack length (longitudinal direction) decreased 1.4 times and 1.44 times accordingly, which is a positive moment in addressing the issue of the localisation and stoppage of a crack fracture in main gas pipelines. Simultaneously, the analysis of the prestressed pipelines model test results on crack fracture propagation showed that single rings are more effective, which decreased the crack opening width by 1.1 times and the crack length up to 1.5. Therefore, the experimental results obtained positively complement the available methods of crack localisation in main gas pipelines, which can be used by engineers and research communities when designing or reinforcing existing operating main steel gas pipelines.

A person's body temperature is an important indicator of their health status. A deviation of that temperature by just 2 °C already has or can lead to serious consequences, such as fever or hypothermia. Hence, the development of a temperature-sensing and heatable yarn is an important step toward enabling and improving the monitoring and regulation of a person's body temperature. This technology offers benefits to several industries, such as health care and sports. This paper focuses on the characterization and development of a hybrid yarn, which can measure and visualize temperature changes through a thermoresistive and thermochromic effect. Moreover, the yarn is able to serve as a flexible heating element by connecting to a power source. The structure of the yarn is designed in three layers. Each layer and component ensures the functionality and flexibility of the yarn and additional compatibility with further processing steps. A flexible stainless steel core was used as the heat-sensitive and heat-conducting material. The layer of polyester wrapped around the stainless steel yarn improves the wearing comfort and serves as substrate material for the thermochromic coating. The resulting hybrid yarn has a reproducible sensory function and changes its resistance by 0.15 Ω between 20 and 60 °C for a length of 30 cm. In addition, the yarn has a uniform and reproducible heating power, so that temperature steps can be achieved at a defined length by selecting certain voltages. The thermochromic color change is clearly visible between 28 and 29 °C. Due to its textile structure, the hybrid sensory and actuating yarn can easily be incorporated into a woven fabric or into a textile by means of joining technology sewing. [ABSTRACT FROM AUTHOR]

This paper reports a new strand wire winding method in a solenoidal coil with limited geometry that enables good impedance matching. In the proposed method strand wires are wound layer-by-layer on top of each other allowing one to set equivalent inductance and resistance of the coil to desired values while obtaining dense magnetic flux and high current carrying capacity. As a proof-of-concept demonstration, simple model setups were constructed with solenoidal coils composed of copper wire strands wound according to the proposed method, and a plastic pipe. The measurements were repeated with a metal shell placed inside the coil to model a complete heating system. System inductance and resistance were measured at two different frequencies. The results show that with the new winding method it is possible to increase a coil’s turn number and the number of strand layers composed by the coil. Also, adding and removing strand layers in the proposed coil architectures enable inductance and resistance values to decrease and increase, respectively, in a controlled way. To understand changes of system parameters, simulations were also performed. The calculated inductance and resistance values in the simulations agree well with the measurement results and magnetic flux distribution created in the system demonstrates the changes.

In order to accurately identify the operating condition of the smoothing reactor， a deep learning method based on CNN （convolutional neural network） is introduced. A voiceprint pattern recognition model for reactor windings using Mel spectrogram is developed. The sound signals are collected using dry smoothing reactors as the experimental object. The Mel filter method is used to convert the collected sound signals into a spectrogram with different working conditions used as the labels of the data set. The CNN algorithm is used to identify the working conditions corresponding to the different signals. The results show that CNN can be used to accurately identify dry voiceprint patterns of smoothing reactors. The optimized neural network can achieve an accuracy of 98.4% in recognition of voiceprint signals under sinusoidal excitation， harmonic excitation and DC bias excitation. The research results provide a potential technical solution for realizing intelligent detection of power grid signals.

The choice of material, manufacturing process, and molding tool significantly affects the quality, environmental impact, and cost efficiency of composite components. Producing one-piece hollow profiles with smooth inner surfaces and undercuts presents major challenges for conventional mold concepts. There is yet no thorough review of shape-variable mandrels in composite manufacturing to be found in the literature. This paper provides an overview of research on shape memory polymers and other shape-variable materials used in tooling applications for composite manufacturing. This work covers shape memory, heat shrink, and other deformable tooling concepts that enable the production of one-piece Type V pressure vessels, air intake ducts, or curved struts and tubes. A systematic literature review in combination with a state-of-the-art open-source active learning tool ASReview is conducted. Fifteen relevant studies were identified. Research on shape-variable tooling is mainly conducted by three research groups in the USA and the PRC. The tooling is mostly made of unreinforced thermosets, especially styrene-based ones. Thermoplastic resins are less common, and reinforcements limit the usable elongation in the temporary shape. The shape variability is either a shape memory and/or a softening process, which, in all studies, is activated by heating. Release agents are widely used to ease demolding. No ecological or economical assessment of the manufacturing methods was conducted in the reviewed studies. Three fields for further research that could be identified are as follows: (1) thorough ecological end economical assessment of shape-variable mandrels in comparison with conventional tooling; (2) thermoplastic shape memory polymer mandrels; and (3) further investigation of simulation capabilities for shape memory mandrels.

Background. In the process of manufacturing transformers, many operations are performed to control technological operations, such as matching the size of the winding wire, its tension, winding density, coil dimensions, location and correctness of transitions from one coil to another, winding direction, soldering and insulation quality. Materials and methods. Various devices are considered, which include a ferromagnetic core with an excitation winding and a reference coil. Devices of this type are usually characterized by relatively small dimensions, which limits the maximum size of the controlled coils, and by an error from a change in the average diameter of the controlled coils due to the non-uniformity of the magnetic field within the working area. An important operation is to check the number of turns of the transformer windings. Results and conclusions. To improve the accuracy of measuring the number of turns of inductors and expand functionality by measuring the number of turns of windings of transformers on toroidal cores after the completion of the winding process, a measuring device was developed with an error of ±2 turns in the range from 100 to 1000 turns, and ±4 turns in the range up to 1000–10000 turns, which allows to reduce the amount of rejects in their production.

The finishing of yarns by bobbin dyeing is of key importance in the value chain of home and apparel textiles. In the bobbin dyeing process, yarn bobbins are placed on dye spindles and passed through with dye liquor. If the winding process parameters are selected unfavorably, the density of the winding package is inhomogeneous. The inhomogeneous density distribution leads to an inhomogeneous flow of dye liquid through the package and, hence, to dyeing defects. In order to minimize dyeing defects and to reduce set-up times, we present a simulation-based parameter recommendation for cross-winding machines in this paper. We use a kinematic model of the winding process combined with an empirical model for the package diameter to optimize the package density distribution. We introduce a criterion to avoid patterning defects and adapt winding settings. For bobbins with Nm 34 Co yarn, the homogeneity of the density was improved and the color deviation was reduced by up to 50% due to these simulation-based setting suggestions. [ABSTRACT FROM AUTHOR]

Filament winding (FW) technique determines the production efficiency of wound products and the bearing capacity of composite layers, so the development and innovation of winding technique and equipment have become the focus of scientific researchers. This paper analyzes the influence of fiber crossing on the composite layers in the single filament winding (SFW) technique, proposes a multi-filament winding (MFW) technique. Firstly, the constitutive model of fiber cross region is constructed from mesoscopic scale, and the influence of this phenomenon on the design of composite layers is illustrated using netting theory. Then, the MFW technique is designed and developed, and the three-point bending test of CFRP is carried out with digital image correlation (DIC) technology, indicating that the MFW technique exhibits superior flexural strength of 483.71 MPa. Finally, a 35 MPa type III vessel is taken as the object for comparative numerical simulation, the results show the stress adopting the MFW technique in the dome section is reduced by 1418 MPa, and is smaller and more evenly distributed in the cylinder section. The MFW technique takes full advantage of the CFRP properties, improves the pressure bearing capacity of composite layers, meets the American DOT-CFFC standard requirements, and reduces the carbon fiber usage. The lightweight design of high-pressure hydrogen storage vessels is realized with a novel idea, and the winding efficiency is greatly improved compared with SFW technique. [Display omitted] • The disadvantages of traditional filament winding technique are revealed. • Multi-filament winding (MFW) technique is proposed innovatively. • The theory of variable yarn thickness and variable yarn width is developed. • The composite layers with MFW technique have a better bearing performance. • MFW technique realizes lighter and more efficient manufacturing of pressure vessels. [ABSTRACT FROM AUTHOR]

Tissue paper is deep-rooted in our daily life because of its different types of products that allow various applications. Tissue paper is a low grammage paper that is mainly characterized by softness, tensile strength, liquid absorption, and elasticity. These characteristics are essential when producing products such as toilet paper, kitchen rolls, hand towels, napkins, and facials. The tissue paper production involves two stages: formation of the tissue paper sheet itself and its converting into different finished products. Converting is characterized by several operations, namely: unwinding, winding, embossing, lamination, perforation, cutting, packaging, and palletizing. The most impacting operation is the embossing, which consists of marking a pattern on the paper sheet by applying pressure, with the intent to produce papers more aesthetically pleasing to the final consumer and/or a way to identify a particular brand. Also, it affects final properties, increasing the liquid absorption capacity and bulk but reducing softness and tensile strength. Converting is complex and has a huge impact on the finished products properties. In this review, the authors explored the different steps of converting and how they impact the different properties of finished tissue products.

Power transformers are inevitably subjected to external short circuit impact during their service period. The electromagnetic force generated by the fault current may cause winding destabilization and collapse. The radial buckling of the inner winding accounts for a considerable proportion. Based on the effective contact of the sticks, the traditional analytical methods ignore the manufacturing deviation and operation impact (MDOI) characterized by assembly gaps and insulation shrinkage. To address the limitation of the contact-constrained approach, this paper proposes the equivalent support stiffness (ESS) analytical method. The ESS method can investigate the issues of support weakening and failure, which are affected mainly by assembly gaps and insulation shrinkage. Further, two transformers are implemented in the short-circuit tests to demonstrate the feasibility of the ESS method. Among them, the assembly gaps are investigated by the first and second windings of the newly manufactured transformer, and the influence of insulation shrinkage is researched through a 30-year-old transformer. Furthermore, the application of the ESS method is expressed based on the tests and the simulations. The research presents quantitative references for transformer design and operational reliability assessment. The ESS method can be an improvement and supplement to traditional methods.

The large thickness COPV is designed by netting theory and the finite element simulation method, but the actual performance is low and the cylinder performance still cannot be improved after increasing the thickness of the composite winding layer. This paper analyzes the reasons for this and puts forward a feasible solution: without changing the thickness of the winding layer, the performance of COPV can be effectively increased by increasing the proportion of annular winding fiber. This method has been verified by tests and is supported by theory. [ABSTRACT FROM AUTHOR]

Sensorless tension control system is investigated for textile processes and machines in this paper. A prototype unit unit was designed and manufactured for this aim. Prototype unit consisted of winding and unwinding warp beams driven by a servomotor and an induction motor. Warp tension was measured by load cells for evaluating the sensorless tension control system performance. Diameters of winding and unwinding warp beams were measured by laser sensors. Wound warp length was measured by an incremental encoder fitted to the shaft of a cylinder rotated by warp yarns. Number of beam rotations of warp beams were measured by separate inductive switches. A software program was developed in LabVIEW to implemet sensorless tension control algorithms and record the performance data. Results showed that the desired tension can be kept constant within 5% deviation limits by the servomotor torque control. [ABSTRACT FROM AUTHOR]

This paper presents an investigation of an axial generator for a small vertical-axis wind turbine. The performance of the axial generator design is tested by knowing the output voltage produced by varying the rotation. The generator is designed to generate three phases of electric power. And then through the wind turbine controller, three phases of alternating current are converted into direct current/DC. The Axial generator uses neodymium permanent magnets with many winding poles of 12 pieces. The coil uses 0.5 mm diameter copper enamel wire with a total of 400 turns each. A voltage of 30 Volt DC is obtained for the rotation of the axial generator at 300 rpm. For application, the generator can be used for a small vertical-axis wind turbine for stand-alone street lighting, which needs only 12 Volt of DC. [ABSTRACT FROM AUTHOR]

The current standard considers the efficiency of electric motors only in terms of power efficiency and does not pay attention to the so-called economic efficiency - the power factor that affects the loss of electricity in the motor supply network and depends on its energy excellence. This ill-considered approach to establishing the energy efficiency class is a significant shortcoming of the European standard and requires its refinement. The single-phase power supply network in housing and communal services has led to the fact that modern motor compressor units of refrigerators, air conditioners, etc. are equipped with single-phase asynchronous electric motors. An innovative single-phase asynchronous AC motor for motor-compressor units of household appliances is considered in the paper. The stator winding of it is composed of two identical series-connected coils enclosed in half-slots of the stator with a spacious offset of 900 . The phase shift of the currents in the coils is provided by a capacitor connected in parallel to one of the coils. The proposed motor is technological in production, has higher specific power and energy efficiency than existing models and meets the IE-3 class energy efficiency. Equivalent electrical circuit and vector diagram of currents for this motor have been developed and shown. They are intended for its mathematical simulation, calculation of static operating characteristics, analysis of dynamic properties at operation in the electric drive system, and also at the level of design work. [ABSTRACT FROM AUTHOR]

Tubular products obtained by winding of fibrous composites are widely used as pressure vessels in aerospace engineering. The method of testing rings cut from tubes for tension in split disks according to ASTM D 2290-12 or ISO 8521:2009 standards is most often used to evaluate the hoop strength characteristics. Tension with bending takes place in the rings in the gap zone of the split disks, which leads to a significant reduction in fracture loads. This work proposes to use a ring specimen with a flattened zone located at a distance from the split-disk gap. The failure in the flattened zone demonstrates high tensile strength values. It is also noted that the friction between the surface of the split disks and the ring has to be minimal. The finite element analysis results help designing a flattened zone of fabric GFRP rings to obtain correct hoop tensile strength. [ABSTRACT FROM AUTHOR]

Copyright of Zhejiang Electric Power is the property of Zhejiang Electric Power Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Despite major progress in the design of power transformers, the Achilles' heel remains the insulation system, which is affected by various parameters including moisture, heat, and vibrations. These important machines require extreme reliability to guarantee electricity distribution to end users. In this contribution, a fiber optic sensor (FOS), consisting of a Fabry–Perot cavity made up of two identical fiber Bragg gratings (FBGs), is proposed, to monitor the temperature and vibration of power transformer windings. A phase shifted gratings recoated sensor, with multilayers of polyimide films, is used to monitor the moisture content in oil. The feasibility is investigated using an experimental laboratory transformer model, especially fabricated for this application. The moisture contents are well correlated with those measured by a Karl Fisher titrator, while the values of temperature compare well with those recorded from thermocouples. It is also shown that the sensors can be used to concurrently detect vibration, as assessed by sensitivity to the loading current. The possibility of dynamically measuring humidity, vibrations, and temperatures right next to the winding, appears to be a new insight that was previously unavailable. This approach, with its triple ability, can help to reduce the required number of sensors and therefore simplify the wiring layout. [ABSTRACT FROM AUTHOR]

There is no doubt that transformer plays a fundamental role in power system. At the same time, transformer winding fault diagnosis is an important topic. Many works put the most emphasis on the identification of fault type and degree, while ignoring the fault location. However, fault location is an urgent problem to be solved, which is worth studying and discussing. The contribution of this paper lies in the location of Disk space variation (DSV) fault. The introduction of digital twin can solve the problem of insufficient fault cases, and pave the way for the intellectualization of fault diagnosis. In this paper, the digital twin of transformer winding is established based on double ladder network, in which the distributed parameters are calculated by finite element method. Frequency response analysis (FRA) is one of the most widely accepted methods for transformer winding mechanical deformation fault diagnosis. Aiming at the interpretation code of FRA, this paper disproves the view that phase information is useful. Then, by extracting the mathematical index of FRA, multi-layer perceptron (MLP) is trained and DSV fault location is realized. In addition, the popular support vector machine is also compared with the MLP model in this paper, which further highlights the advantages of MLP. The proposed method is verified by an actual transformer, and the results are satisfactory.

Blood oxygenators involve a complex network of hollow fibers for efficient gas exchange with blood. The optimal microstructural arrangement of these fibers is an ongoing research interest. While the fiber systems of commercial oxygenators are manufactured to address mass production, the research oxygenator prototypes demand more flexibility so that different design parameters can be tested. Here a hollow-fiber assembly system is designed and built for winding research grade extracorporeal blood oxygenator mandrels at different layout dimensions so that these different configurations can be evaluated for mass transfer capacity and blood damage. The hardware design and manufacturing details of this system presented together with its impact on the prototype oxygenator device assembly process. This in-house built system can wind thin fibers, having outer diameters ranging from 100 μm to 1 mm, at any specified winding angle continuously. A control system for fiber stress is also incorporated to eliminate fiber damage. Our system consists of three main units: (1) unwinding, (2) accumulator, and (3) winding systems, integrated together via the control software. The unwinding unit has a PID controller to maintain the position of the accumulator motor on the reference point by tuning the velocity of feeding fibers to the accumulator unit. Another PID controller preserves the desired tension value of the fibers by adjusting the position of the accumulator motor. Desired tension value is defined by the user and typically obtained through uniaxial testing of fibers. The control unit employs a “cascaded” PID controller since the PID controller in the accumulator unit maintains the tension and the PID controller in the unwinding unit controls the position of the accumulator motor. Finally, the winding unit utilizes two motors to wind the fibers over the outer diameter of a mandrel at the desired winding angle. The first motor drives the translational movement, and the second one provides mandrel rotation. The desired angles are achieved by tuning the synchronous movement of the winding motors. While the system is designed to produce assembled blood oxygenator mandrel prototypes, this concept is also applicable for producing cylindrical fiber-reinforced composite materials with specified fiber angles and stents winded on jigs.

We consider the unmanned aerial vehicle of a multicopter type, in which the on-board battery is recharged using the energy of an external electromagnetic field created by the currents flowing through the wires of the contact network of an electrified railway transport or an overhead power line. This process is carried out without interrupting the flight of the aerial vehicle. The process of transferring this energy to the board of the multicopter is carried out by inductive method using an electric winding placed on it. This winding is connected to the battery. We constructed the finite element mathematical model. We performed the calculations of the EMF induced in the winding at the different trajectories of the aerial vehicle near the contact wire of the railway. It is revealed that the highest EMF values in the winding are induced when flying under the alternating current contact wire. When the winding moves under the direct current wire the frequency and amplitude of the induced EMF depend on the period of deviations of the aerial vehicle from the direction of the axis of its straightline movement. The EMF curve is non-sinusoidal. The degree of distortion of the EMF curve depends on the amplitude of the deviation of the winding from the axis of the direction of movement. At the alternating current through the contact wire the amplitude of the induced EMF mainly depends on the amplitude and frequency of the external magnetic field created by this current. The movement parameters of the aerial vehicle have a negligible effect on the EMF value.

Introduction. With the adoption of standards to reduce losses in transformers it is necessary to change the design of transformers that remain unchanged. Further energy saving is possible with the use of non-traditional technical solutions for the improvement of transformers. Problem. In order to reduce idle losses, the curved magnetic circuits of power transformers are carried out in the form of low-volume circuits. Windings are injected into assembled magnetic conductors by shuttle machines. The shuttle of windings provides technological gaps in winding windows, which results in an increase in size, metal capacity and losses. Goal. Rationale for transformer performance improvement by excluding process gaps in winding windows. Methodology. The definition of the change in transformer indicators is performed using optimization functions of the dimensionless indicators of the technological level. The adequacy of the functions is confirmed by the calculation of the mass of the electromagnetic system and the losses of the transformer. The figures of the compact analogue are calculated from the named serial analogue. Results. The result is a reduction in mass and a loss in the compactness of the transformer. Originality. The improvement of the indicators and the simplification of the winding technology are provided by a change in the design of insulating frames of winding coils. Winding on the rods is ensured by rotating the outer part of the composite insulating frame. Practical significance. Replacement the design of the windings of transformer with power of 40 kVA of 1000 V voltage class with a spatially twisted, small-dimensional magnetic conductor on a compact analogue leads to a reduction in mass and overall dimensions by 15 % and (17-18) %. Efficiency increases by 0.3 %.