Iet Science Measurement & Technology最新文献

In order to solve the problem of remote oil level measurement for unmanned transformers, this paper proposes an online monitoring technology for transformer oil level based on ultrasonic sensors. Subsequently, a finite element model and experimental testing platform were constructed to analyse and verify the influencing factors of the transformer oil level sensors. The results indicated that there is a lower measurement error at 140 kHz in the ultrasonic frequency range of 20–320 kHz, which can be selected as the recommended frequency. The impurities in the oil and the thickness of the tank wall have a slight impact on the accuracy of oil level measurement, and can lead to a decrease in the signal-to-noise ratio of the echo. Furthermore, as the speed of sound increases by about 4 m/s, for every 1°C increase in oil temperature, it is necessary to calibrate the measurement results based on the oil temperature. The test results of actual experimental transformers showed that the designed online monitoring device can achieve high-precision monitoring of transformer oil level, with a relative error generally less than 3%.

This article develops a method for recovering a one-dimensional rough surface profile from scattered wave field, using a single receiver and repeated measurements when the surface is moving with respect to source and receiver. This extends a previously introduced marching method utilizing low grazing angles, and addresses the key issue of the requirement for many simultaneous receivers. The algorithm recovers the surface height below the receiver point step-by-step as the surface is moved, using the parabolic wave integral equations. Numerical examples of reconstructed surfaces demonstrate that the method is robust in both Dirichlet and Neumann boundary conditions, and with respect to different roughness characteristics and measurement noise.

A slight turn-to-turn short-circuit fault in the incipient stage does not trigger fuse protection, and the regular transmission and transformation functions of the transformer within the power grid are not affected very much by the incipient turn-to-turn short-circuit fault. Therefore, the incipient turn-to-turn short-circuit faults are often undetected, resulting in massive accidents. Incipient turn-to-turn short-circuit faults lead to localized overheating in the transformer, which changes the transformer's oil-tank surface temperature (OTST). A thermal simulation model (TSM) is presented. Based on the TSM, OTST data with different load rates and fault parameters are collected. The steady-state and transient characteristics of OTST are analysed by extracting the OTST feature vector and the temperature difference of specific regions. The results show that the growth of the heat production value of faulty coils causes a rise in the OTST; higher faulty coils' locations lead to wider OTST differences; the temperature difference's area S can follow the incipient short-circuit fault in the first 20 min after it occurs, which is faster than the top oil temperature. This study gives insight into the thermal behaviour of OTST, assisting in fault detection and location at the incipient fault stage.

Simultaneous electromagnetic field probing system (SEMPS) has been popular in recent years. Herein, a simultaneous electromagnetic field probing system with Y-shaped separation detection structure (SEMPS Y) is first proposed, in which the electric field probing region and the magnetic field probing region of the probe are separated by completely covering the shield along the loop and adding a pin-shaped metal wire to capture the electric field, which are not the same as the classical dual probe structure. Combined with the non-rotating asymmetric calibration method (NRACM), a 4-port vector network analyser (VNA) and a highly symmetric grounded coplanar waveguide (GCPW) calibrator are used to solve the calibration matrix of the asymmetric SEMPS Y. The high symmetry GCPW calibrator is used to generate the standard electromagnetic field for calibration. The results of standing wave measurements show that the SEMPS Y can achieve ultrawideband electromagnetic field measurement of up to 20 GHz. Based on near-field scanning measurements, SEMP Y can obtain results consistent with the calculation. In addition, when the probe is rotated 90° to invalidate the H-field input, the decoupling curves of E-field and H-field are measured. Results show that the separation detection structure can effectively solve the cross-coupling problem.

Bearing-fault diagnosis in rotating machinery is essential for ensuring the safety and reliability of mechanical systems. However, under complicated working conditions, the number of normal mechanical equipment samples can far exceed the number of faulty ones. When the data are so imbalanced, data fault diagnosis cannot be easily conducted using conventional deep learning methods. This study proposes a fault diagnosis method based on a dual-branch interactive fusion network, which improves the accuracy and stability of bearing-fault diagnosis. First, a dual-branch feature representation network comprising an iterative attention-feature fusion residual neural network and a long short-term memory network is designed for extracting different modal features. Meanwhile, intermodal fusion of the extracted features is performed through multilayer perception. Based on the cost-sensitive regularization loss, a new joint loss function is then designed for network training. Finally, the effectiveness of the proposed method is verified through comparative experiments, visualization analyses, ablation experiments, and generalization performance experiments.

The contact finger electrical connection structure is a crucial component of high voltage bushings, and its safety and reliability directly impact the operational stability of the bushing. To investigate electrical contact performance of the contact finger under eccentric conditions, a three-dimensional electrical, thermal, and force multi-physics coupling calculation model was established. Additionally, a test platform was constructed to measure electrical contact characteristics of the contact finger. The contact characteristics of the contact finger when the male head was axially deflected and radially offset compared to the female head were obtained. The research findings indicate when the male head deflects axially, the contact force changes of the contact finger blades on both sides are opposite. Moreover, as the axial deflection angle of the male head increases, the resistance of the electrical connection structure shows a rising-slow decreasing-fluctuating trend. The resistance is highest at 3°, with a resistance increase rate of 7.35%. Furthermore, the resistance of the electrical connection structure varies with the radial offset of the male head, following a power function. Contact failure occurs when the radial offset is 1.31 mm, and the resistance increase rate reaches 24.9% at a radial offset of 1.58 mm.

Cross-linked polyethylene (XLPE) cables are commonly used for constructing urban power lines due to their superior properties. Insulation defects can cause partial discharge (PD) and electrical tree, which can negatively impact the insulation performance of the cable and even lead to insulation failure. During operation, cables undergo hot and cold cycles, and the temperature of the insulation layer can affect the PD and electrical tree. An experimental platform with a needle-plate electrode was developed to investigate this phenomenon. The platform was used to detect PD activity and electrical tree propagation in XLPE under a 50 Hz voltage at various temperatures. The results indicate that an increase in insulation temperature leads to an increase in the number of PDs and a decrease in the inception voltage. Simultaneously, it has been observed that a rise in temperature can facilitate the spread of electrical trees. To explicate the aforementioned PD result, a finite element analysis (FEA) model has been developed. Additionally, a molecular dynamics (MD) model of XLPE material was developed to clarify the phenomenon of electrical tree propagation. This study's findings aid in investigating the impact of temperature on XLPE defects, which is critical for assessing power cable performance.

The power frequency electric field is the most important electromagnetic environmental factor in alternating current power transmission projects. The humidity has a negative influence on available electric field measuring devices, which may lead to discrepancies of up to seven times the actual value at a relative humidity exceeding 80%. The changes in the support and probe shell impedance may be the reason for the error. The optimization measures include modifying the communication mode, designing a suitable structure and circuit for the probe, and using composite insulating material with strong hydrophobicity for the support. A three-axis omnidirectional electric field measuring device was developed based on wireless communication and composite support. The variation of the measured electric field strength value is less than 1% at relative humidities ranging from 45% to 90% in the laboratory, and the measured results obtained in high humidity at the high-voltage test site and under the transmission line demonstrated high accuracy. The research demonstrates that the composite support can be used to improve the performance of conventional devices. The proposed device can better meet the needs for accurate measurement of electric field strength in a high-humidity environment and overcome the technical problems raised by the IEC standard.

Travelling waves in circuit chains are studied to measure continuous dispersion. A lock-in frequency meter (LIF) is suitable for precisely determining k for each set $�\omega$ of waves in finite alternate LC chains, where LIF has been proven to be more accurate than the fast Fourier transform. In addition to the $�\omega$–k measurement, the wave impedance spectrum of the travelling wave can be measured simultaneously, for investigating the dispersion and splitting of pulse propagation. The measured dispersion is validated to be consistent with the derived theoretical equations. The result provides an independent way to precisely obtain dynamical system properties for chains composed of non-ideal components, such as resistors for researching non-Hermitian behaviour under dissipation. Systematical mapping of relative deviation dependence of wave dispersion measurement with LIF on different chain length and component variation is studied, indicating boundaries of 1%, 0.1%, and 0.01% precision for guidance of experiments.

The problem of crystal ice formation inside aircraft turbine engines is well-documented, and poses a significant risk to safety. The problem is not only one of power loss in flight, but the very real possibility that a flame-out event could occur due to ice accretion on compressor stators, with potentially catastrophic outcomes. Although many instrumentation systems have been developed for wing ice detection, incipient formation of crystal ice is somewhat more difficult to detect. This is compounded by the need for a noncontact sensor which is robust to in-flight conditions. This paper proposes an approach to the detection of ice formation based on microwave transmission characteristics across the first and possibly the second stage of the compressor stator. It is shown that noncontact detection is feasible under realistic conditions. The contribution of this paper is twofold. First, the microwave transmission approach is motivated using wind tunnel measurements, and appropriate frequency bands are determined. Next, a signal processing approach involving higher-order analysis of time-frequency distribution characteristics is then put forward. Experimental results are presented to support the hypothesis that multiband detection offers a workable approach to the incipient crystal-ice detection problem.