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A new testing method (oscillating wave method) has been proposed as a solution to the problem of short maintenance time in the traction power supply system, which could complete tests of winding and insulation via one connection and improve the maintenance efficiency of the transformer. Through the method being proved highly sensitive to winding faults, the variation under different winding states, however, remains unclear. This article aims to analyze oscillating wave signatures in the occurrence of axial displacement (AD). First, the modeling method will be proposed that can simulate oscillating wave signatures in different winding states. Then, the time-domain feature and the new proposed frequency-domain feature are applied to analyze the fault extent and location of AD fault. The results show that this model accurately simulates oscillating wave signatures. Moreover, the time-domain feature [Euclidean distance (ED)] is closely related to fault extent. The combined use of the time-domain feature (ED) and the frequency-domain feature (W-Energy entropy in Z-Score) is effective in the identification of fault location. These features, therefore, can provide the reference for winding state evaluation. [ABSTRACT FROM AUTHOR]

Thermal analysis is a key aspect in electrical machine design and for those operating with severe duty where a high-reliability thermal analysis is required. This paper presents a comprehensive analysis of techniques for calibrating generic thermal model of electrical machines. The proposed approach combines two existing experimental methods commonly used in thermal testing of electrical devices. The first method uses a short-duty transient excitation to derive the winding thermal parameters, whereas the second method uses a steady-state excitation to estimate the thermal parameters related to the heat transfer from the winding. Both experimental methods are based on a well-defined heat source provided by a constant current (dc) excitation. For reference, alternative existing methods for calibrating thermal models, are usually combining the winding thermal data predictions and a set of experimentally derived temperatures from dc tests. Such approach, however, might be inadequate if not supported by extensive experimental data. This frequently leads to a significant rate of inaccuracy, thus having a significant impact on the reliability of temperature predictions. The main advantage of newly proposed approach is the reducing of the number of variable parameters and a more systematic calibration process. Additionally, a detailed test procedure for generic thermal model calibration is presented and discussed. [ABSTRACT FROM AUTHOR]

The electrical–mechanical dynamics of a transformer may be described by a model with cascade-connected linear and nonlinear parts. This paper shows that mechanical faults have a significant influence on the linear part of the model. A change in the system order of the linear part of the model can be used as an indicator of variance in a transformer’s physical characteristics. A technique based on the Lipschitz criterion is developed to estimate the system order, which is then used for detecting changes in the vibration of the system caused by mechanical faults in the windings. The proposed method is tested on a three-phase power transformer, demonstrating promising detection of faults in transformer windings. [ABSTRACT FROM AUTHOR]

In this study, we propose a model-based taper tension profile that minimizes residual and radial stresses. In contrast to the constant torque and hyperbolic taper profile, the developed model can accurately decrease the winding tension depending upon the final decrement set by a user regardless of the maximum wound radius. Moreover, the model steeply decreases the winding tension in comparison to other tension models in the early stage, consequently, decreasing the residual stress and maximum radial stress. A hybrid model that combines the developed and conventional taper tension models is developed to expand the range of application of the model. A winding tension maker that applies the model to the winding tension controller is also developed. A variable transformation model that transforms the input of the developed model (radius ratio) to the winding time, which can be easily obtained without any sensors, is obtained. The developed model and winding tension maker are applied to an industrial roll-to-roll thin film winding machine. It is observed that local deformation in a wound thin film generated by the excessive radial stress is improved. A control technique is selected considering film characteristics, and a winding tension controller is designed using the developed tension models and winding tension maker. The designed winding tension controller decreases the maximum radial stress by 38% when compared to the case before application. Moreover, the winding length with few local deformations increases from 100 to 500 m; this confirms the superiority of the developed model and controller. [ABSTRACT FROM AUTHOR]

Electromagnetic design of a moving magnet frictionless linear actuator with self‐holding functionality for mechanical gear shifting in a transmission application is presented. The actuator consists of a tubular magnetic circuit with stationary armature and axially moving rotating permanent magnet assembly with radial magnetisation in the air gap. The armature contains a two‐piece magnetic core with a space for a winding. The effects of armature slot opening and magnetic circuit materials on the self‐holding force and the acting force are studied in the whole moving range. The designed moving magnet linear actuator improves the performance of the vehicle by enabling shift times below 50 ms with no energy consumption between the shifts. [ABSTRACT FROM AUTHOR]

The poloidal field (PF) coils are one main subsystem of the ITER magnets. The PF6 coil is being manufactured by the Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP) as per the PF coils cooperation agreement between ASIPP and Fusion for Energy. The ITER PF6 winding pack is composed by stacking nine double pancakes. Dummy double pancake fabrication aims to fully qualify the critical fabrication processes, before series production. This paper describes ITER PF6 dummy double pancake winding process and results, which was performed with a “two-in hand” configuration. Conductors were wound sequentially in the following steps: despooling, straightening, ultrasonic cleaning, sandblasting, bending, and turn insulation wrapping until deposition on the winding table. Joggle bending, helium inlet manufacturing, and tail assembly were also carried out during winding. The dummy double pancake winding was finally completed with the qualification requirements well met, which demonstrated good synchronization of the control system, fine conductor positioning accuracy, tight radial buildup, and so on. [ABSTRACT FROM AUTHOR]

This paper presents the validation of a first-order winding thermal model in machine operative conditions. The proposed model can be used in motor control strategies for the winding temperature prediction during transient overload, or vice versa, for the prediction of the maximum time duration of the overload maintaining the winding temperature within the limit imposed by the class of insulation. The thermal model has been validated using two different electrical machines. The first one is a 10-kW automotive starter-generator prototype for mini-hybrid powertrain equipped with distributed bar windings, while the second one is a 2.2 kW total enclosed fan cooled industrial induction motor equipped with conventional stranded wire windings. Depending on the application for both machines, a short-duty transient operation in overload conditions could be required. In particular, the automotive starter-generator must accomplish engine cranking and torque assistance during the vehicle acceleration and braking, while the industrial induction machine could operate in intermittent service in overload conditions when used in machine tool applications. As a consequence, an accurate stator winding temperature prediction is mandatory to fully exploit the machine performance. For both motors, the thermal model parameters have been evaluated by fast experimental approach, and, subsequently, the model has been validated during operative overload conditions. [ABSTRACT FROM AUTHOR]

The sensor which consists of many conductors wound on the rectangular insulated material is employed to detect partial discharge (PD) in the 11.4 kV cast resin power transformer. To examine the effect of winding on the propagation of PD-induced field, the verification tests are performed in free space. According to the structure of transformer, we simulate partial discharge occurs inside the winding and outside the winding to examine the effect of winding to the propagation of PD-induced field. The results show that the PD-induced field can pass through the winding and detected by the coil sensor. In on-line application, to detect PD, three similar rectangular sensors are installed near the surfaces of the 11.4 kV power transformer. From the amplitude variation of PD signals, the imperfect power transformer is clearly identified. However, there is not any image appear on the surface of this power transformer. After 3 years, this power transformer is completely destroyed. [ABSTRACT FROM AUTHOR]

A practical and novel technique to compute the leakage reactance of step lap-core power transformers is presented. It can be applied to helical or continual disc windings. The developed technique is based on computing the magnetic flux lines produced by each active conductor in the windings. Thus, the magnetic linkages are obtained by applying the concept of geometric mean distance of rectangular areas to the magnetic potential. The obtained analytical formulae enable straightforward calculation of the transformer reactance with better accuracy than traditional methods currently used in the design of power transformers. Leakage reactance was computed for 12 power transformers with different coil configurations, and the results were compared with results calculated from the short-circuit test. A difference of no higher than 3% was obtained between values measured with our proposed technique and values calculated with the short-circuit test. [ABSTRACT FROM AUTHOR]

Because high-temperature superconducting (HTS) coils possess low-resistivity, large-current-carrying, and state transition characteristics, the design of HTS transformers is much different from that of conventional ones. The general design of 10.5-kV/1250-kVA HTS transformer is given first. In the electromagnetic design of the 1250-kVA HTS transformer windings via field-circuit coupling simulation, the influence of leakage magnetic field on the critical current of tapes and the circulating current of parallel branches was considered. Moreover, the transient stability of transformer windings combined with superconducting fault current limiter in the HTS power substation is discussed. Based on electromagnetic analysis, the primary and the secondary windings are constructed, and a special transposed method for double pancakes wound with four parallel tapes is proposed. Finally, the current-carrying ability of the primary and the secondary windings is tested in 77 K. Their critical currents are higher than 200 and 3200 A, respectively, which is enough in rated operating condition. [ABSTRACT FROM PUBLISHER]

Diffraction of Ultra-High-Frequency (UHF) electromagnetic waves generated by partial discharges (PDs) inside a transformer will decrease the amplitude when passing through the winding and delay the arrival time of initial wave at the UHF sensors installed on the internal wall of the tank. It may be difficult to locate PDs inside the winding based on detection of UHF signals. To study the feasibility of locating PDs inside the winding using UHF methods, the propagation of UHF wave through windings was simulated by the XFDTD software and the cause of arrival time delay was analyzed by a geometric model. Experiments were carried out on a 220 kV oil-immersed transformer to test the measurement sensitivity and the location accuracy of UHF method for PDs inside windings. The theoretical research results indicated that the UHF wave passed through windings along broken lines, and the propagation time from the PD source to UHF sensors was compared to the time of wave travelling along a straight line. It was found that the arrival time delay caused by diffraction was less than 1ns. The experimental results showed that PDs about 500 pC inside the windings could be detected and located. The amplitude of the UHF signal decreased by about 18 dB, the errors of time difference measurements were less than 0.5 ns, and the location errors were less than 0.1 m. [ABSTRACT FROM AUTHOR]

This article describes an investigation of the transformer inner winding deformation, using Sweep Frequency Response Analysis (SFRA). The object of the investigation is a transformer model with functionality of disassembling inner winding and changing configuration of its parts. The purpose of the investigation is to find the characteristic frequency ranges which could be treated as diagnostic bands. [ABSTRACT FROM PUBLISHER]

In a hard disk drive (HDD), the zero crossing points (ZCPs) of back-EMF generated in the spindle motor armature windings are used as rotor position signal for realizing precision motor speed control. The error of ZCP is a major concern, especially for HDDs with ultrahigh data recording densities. In the paper, several causes that induce the ZCP error are analyzed, and these problems are induced during the motor design and production. Both the analytical and numerical methods are used in the analysis to study the influence of the electromagnetic structure on the ZCP. Solutions are then proposed to reduce the errors of the ZCP during the motor design phase. [ABSTRACT FROM AUTHOR]