Search

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]

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]

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]

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]

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]

Alternating current (AC) copper losses in motors increase with carrier frequency of the pulse width modulation (PWM) and are further increased by leakage flux of the permanent magnet. Therefore, AC copper losses increase with motor speed. Conventional techniques for reducing AC copper losses tend to increase other losses. In this paper, AC copper loss was reduced by wrapping a magnetic tape made of a magnetic composite material around the winding. This method controlled the flux path through the winding. Magnetic composite materials are mixtures of magnetic powders and liquid resins whose magnetic properties can be manipulated by changing the combination and other factors. When Fe–Si–Al magnetic tape was wrapped around the winding, the AC copper loss was reduced by 40%. The loss was further reduced by optimizing the magnetic properties of the magnetic composite material. The AC copper loss was maximally reduced when the specific permeability was 100 and the saturation flux density was 1.6. Magnetic tapes composed of magnetic composite materials with high saturation flux density and specific permeability reduce the AC copper losses without increasing other losses in the motor. [ABSTRACT FROM AUTHOR]

The operating condition and structural state of the converter transformer are closely related to vibration. Abundant harmonics aggravate the vibration of windings and iron cores, resulting in frequent mechanical structural failures, which seriously affect the stable operation of the power system. Traditional research mainly focuses on the vibration of AC transformers without harmonics and there is no in-depth discussion of the vibration mechanism and the numerical calculation model of windings and iron cores under harmonics. In addition, the influence of harmonics, winding connection method and other factors on the vibration characteristics are not clear. Therefore, this paper analyzes the voltage and current harmonic components and contents, establishes a harmonic-vibration numerical model and compares the vibration time-frequency characteristics with or without harmonics and different valve side winding connections through vibration measurement experiments. Finally, a combined simulation analysis reveals the contribution of the windings and core to the tank. The results show that the tank vibration amplitude and dominant frequency will increase under harmonica and the valve side current will affect the dominant frequency. Among these results, when there are harmonics, the amplitude increases by three times, the vibration dominant frequency changes from 100 Hz to 400 Hz and the frequency spectrum widens to 2000 Hz. In particular, the contribution of the winding vibration under the harmonic current will exceed the iron core. The research results reveal the influence of converter transformer harmonics on vibration, which can provide a theoretical basis for numerical calculation of vibration and monitoring of operating conditions and guide the design of structural vibration reduction to reduce mechanical failures caused by vibration. [ABSTRACT FROM AUTHOR]

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.

The usage of multiphase electrical drives expands the operation possibilities of electrical machines and opens new directions of research on inverter-fed electrical machines. With an increasing number of phases, the standard approach of the electromagnetic design of machines has to be generalized to m-phase systems, which is not usually respected in the literature focused on electric machine design, and it is rarely published. This paper summarizes the specific problems linked with the design of machines with different numbers of phases, focusing on the winding design and the calculation of equivalent circuit parameters. In addition to the direct effect of different numbers of phases, the impact of injecting higher order time harmonic components on the electromagnetic design of electric machines is analyzed. The obtained analytical results are verified by the measurement of a nine-phase experimental induction motor. [ABSTRACT FROM AUTHOR]

The shape and attitude (S&A) of the electrode wire are important characteristics of micro coreless motor winding. The purpose of this paper is to present the design of a robotic micro-manipulation system for micro wire carding with arbitrary S&A, which can be used as the pretreatment system for wire micro-gripper systems. The system is based on the principle of flexible carding, and uses nylon, bristle, nanometer-silk and wool as materials for the brushing micro-manipulator. The trajectory of the brushing micro-manipulator is designed, and the S&A of the electrode wires are straightened through the combined motion mode of horizontal and vertical brushing micro-manipulators. The experimental results show that the material of the brushing micro-manipulator has a great impact on the carding quality. Nanometer-silk material is more suitable for horizontal brushing micro-manipulators, and wool material is more suitable for vertical brushing micro-manipulators. The geometric dimension of the brushing micro-manipulator also affects the carding quality. When the diameter is in the range of 1 mm, the carding effect of the horizontal brushing micro-manipulator with a length of 4.9–8 mm is better. The system can realize the automatic carding of flexible electrode wires with arbitrary S&A, and it will not damage the structure of wires in the process. [ABSTRACT FROM AUTHOR]

The control methods of asynchronous motors have changed during past decades. In the past, asynchronous motors were connected to grid directly. Later, thyristors as switching element-based frequency converters for asynchronous motors have appeared. Today, asynchronous motors are controlled with variable speed drives that are frequency converters consisting of IGBT power modules as switching elements that form the output voltage for asynchronous motors. Because of IGBT's high switching speed of around few kilohertz, higher order harmonics appear in the output voltage. Their influence was not analyzed in the past as the methodology of asynchronous motor winding resistance measurement was under development. In this article, a new methodology of motor resistance measurement for mass production is introduced. The resistance—compared to higher order harmonics values between the windings of benchmark and tested motors—gives an ability to faster and more accurately determine a motor's characteristics and losses induced by higher order harmonics that appear when a motor is powered by a variable speed drive. Motor winding's inductance dependency on the current of magnetic biasing and the higher frequency of voltage is analyzed in this article. In addition, the simulation model of resistance to higher order harmonics of motor measurement is introduced and analyzed in this article. [ABSTRACT FROM AUTHOR]

Power transformer is the most important and expensive equipment used in the electric power industry. Fiber Bragg grating (FBG) sensors has stood out as a flexible and particularly suitable tool for power transformer monitoring being a passive and dielectric sensor element. In this work we evaluated the performance of FBG pressure sensors developed to monitor the static and dynamic pressure in high voltage winding transformers during events such as short-circuit and inrush current. Two types of sensors packaging materials were evaluated in laboratory: polyether ether ketone (PEEK) and transformerboard (TB). The sensors have been tested for high intensity and short duration impacts similar to those occurring in short circuits. In addition, we evaluated the time response of sensors using an interrogation system with a 5 kHz sweep in order to analyze the short circuit response time properly. The results pointed that FBG pressure sensors using PEEK and TB are suitable for transformer winding monitoring. The static sensitivity obtained to PEEK based sensors was 0.911 pm/N, in the range of 800 N to 1500 N. This sensitivity is 4.47 higher than TB based sensors sensitivity. Dynamical tests performance showed an excellent repeatability for both sensors, in agreement with static observation. [ABSTRACT FROM AUTHOR]

Accurate calculation of the vibration mode and natural frequency of a motor stator is the basis for reducing motor noise and vibration. However, the stator core and winding material parameters are difficult to determine, posing issues which result in modal calculation bias. To address the problem of calibrating the stator material parameters, we developed a parameter correction method based on modal frequency. First, the stator system was simplified to build a stator system finite element model. Secondly, the relationship between modal frequency and material parameters was analyzed by finite element software, the relationship between modal frequency and material parameters was derived, and the anisotropic material parameter correction method was summarized. Finally, a modal experiment was carried out by the hammering method, and the simulation and experimental errors were within 3%, which verified the accuracy of the finite element model. The proposed correction method of anisotropic material can quickly determine the stator material parameters, and the stator core and winding anisotropic material can ensure the accuracy of the modal analysis. [ABSTRACT FROM AUTHOR]