Search

The Potential Transformer (PT) plays an important role in the measurement and monitoring of the power system. The accurate modeling of the PT is very important but not yet perfect. The stray capacitance will have a non-negligible effect on the performance of a PT. However, the influence of stray capacitance is rarely considered in existing models, which makes the broadband simulation performance weak and provides limited references in engineering. In this paper, a calculation method of PT stray capacitance is proposed to analyze the performance of the PT at different frequencies and extract the capacitive current of the PT port. This paper used a non-destructive method to obtain the test data of a PT, calculated the value of the stray capacitance, and drew the hysteresis loops of the iron core. A corresponding simulation model was established to predict the PT performance at different frequencies. The simulation results are in good agreement with the experimental data, which proves the accuracy of the modeling parameters. The data processing logic is clear and is easy to be simplified by programming, which makes it promising in engineering. [ABSTRACT FROM AUTHOR]

It is essential to carry out an AC voltage withstand test after GIS extension and maintenance. At present, the common methods of GIS AC withstand test include double isolation gap, reduce the test voltage, and narrow test range. These methods generally have some defects: such as complex test processes, all bus de-energized, some apparatus failed to test, unreliable test results and so on. This paper presents a distinctive GIS AC voltage withstand test method. The method controls the phase-frequency parameters of the test voltage so that it maintains the same phase-frequency relationships as the in-service bus voltage during the process of testing. In this situation, the GIS can carry out an energized AC voltage withstand test. The process of AC withstand voltage test method based on phase-frequency control (PFC) is introduced in detail, and the feasibility of this method is verified. The phase difference margin of the PFC method is optimized through simulation and numerical calculation, and a variety of protection measures are proposed to ensure the safety of the test process. The proposed PFC AC voltage withstand test method will not affect the in-service bus and has great practical application value for the field GIS AC voltage withstand test.0F. [ABSTRACT FROM AUTHOR]

The grand challenge toward the miniaturization of untethered robots is the lack of a proper actuation system that can effectively transform the limited onboard energy into an untethered movement of the whole body. Here, in this article, we present an insect scale, 5-mm-long, and 9.4 mg in body mass untethered crawling robot powered by a 37 mg onboard ceramic capacitor. With high electromechanical efficiency by utilizing self-excited electrostatic vibration, the prototype device can be directly powered by an onboard capacitor without any boost or frequency conversion circuitry, and forward movements have been achieved at an average moving speed of 5.9 mm/s for 1.68 s. The maneuverability of locomotion from solid ground to water and different moving directional controls via the leg designs have been demonstrated for the advancements in the field of millimeter-scale robotics research. [ABSTRACT FROM AUTHOR]

Most of the available overvoltage sensors are too sensitive to the installation angle and inducing direction. Even a slight angular deflection will cause a nonnegligible error to the measurement. To reduce the impact caused by angular deflection, in this article, we propose a new spherical six-electrode overvoltage sensor to improve the measuring accuracy and stability. First, we presented the 3-D electric field ($E$ -field) coupling mechanism, vector synthesis method, design, and output properties of the proposed sensor. Second, we obtained the relationship between the structural parameters and the equivalent capacitance by the finite-element method (FEM). Finally, we completed the steady-state test, transient test, and 3-D angular deflection test. From the results, the sensor has a broad bandwidth of 1.2 MHz, a phase error of less than 1.8°, and good linearity of the output signals. In the case of 3-D angular deviations, the mean relative error (MRE) of the sensor is lower than 2.55%, with a maximum standard deviation (SD) of 0.088%, which proves that the output of the proposed sensor is well consistent with the overvoltage signal, and its accuracy is almost immune to the angular deflection. [ABSTRACT FROM AUTHOR]

The early screening and prevention of chronic respiratory diseases are very important. To achieve the monitoring and management of chronic obstructive pulmonary disease (COPD), this article proposes a new lung impedance measurement method, which uses a cross four-electrode structure. It effectively solves the problems of noncompliance of traditional instruments, risk of cross-infection, and nononline monitoring. Compared with the traditional impedance measurement method, the measurement accuracy of lung function parameters is improved. Using the detection device, the equivalent impedance of the chest was rapidly measured from two orthogonal directions when the people were in the same breath state. The maximum expiratory and inspiratory thoracic impedance was obtained by analyzing 30 samples. The measurement of lung function parameters is realized by solving the change value of impedance and its relationship with the chest circumference. Experiments proved that the cross four-electrode method could consider the two directions of equivalent thoracic impedance, enrich the measurement parameters of thoracic impedance, and make the test results of pulmonary function parameters have good consistency with the results of standard methods. Correlation coefficients of test indexes forced vital capacity (FVC) and forced expiratory volume in one second (FEV1) were 0.967 and 0.955 respectively. The consistency boundary diagram showed that more than 95% of monitoring data of the subjects fell within the scope of the consistency boundary, and the maximum relative error of measurement was only 4.65%. [ABSTRACT FROM AUTHOR]

At present, the method of obtaining the voltage of transmission lines by using the inverse problem of the electric field is generally faced with the difficulties of solving data equations. Aiming at the above problems, the method that solves transmission wire voltage through spatial electric field integration based on D-dot sensor is proposed. In this paper, with the ground as the reference potential and the vertical line of the transmission line to the ground as the integral path, D-dot electric field sensor is applied to measure the instant electric field values of several nodes on the integral path and the transmission wire voltage is directly solved combined with Gauss–Legendre numerical integration algorithm. The Gauss–Legendre algorithm is verified by the electric field distribution data on the integration path obtained by simulation. Furthermore, the improvement of the Gauss–Legendre algorithm is realized through optimizing the integral interval so that the location of integral nodes is more reasonable. Finally, the measurement system based on LabVIEW is designed and the experiment platform of the analog transmission line is constructed. Experiment results show that the measurement method of transmission wire voltage through the improved Gauss–Legendre algorithm based on D-dot sensor owns high accuracy with an error of less than 1%. [ABSTRACT FROM AUTHOR]

In modern mobile communication networks, such as 3G and 4G networks, sectorized antennas have been widely used to divide each cell into multiple sectors in order to improve coverage, spectrum efficiency, and quality of service. Large-scale path loss from a transmitting antenna to a receiving antenna should include: 1) propagation attenuation that depends on transmission distance; 2) shadowing that depends on surrounding environment; and 3) antenna loss that depends on a sectorized antenna pattern and transmission angle. An in-depth analysis of statistical characteristics of large-scale path losses involving with these three factors is crucial for the design, operation, evaluation, and optimization of modern sectorized wireless networks. In this paper, a sectorized antenna pattern is, for the first time, considered in the derivation of a closed-form expression of a probability density function (pdf) of large-scale path losses. Specifically, we first discover that the normalized pdf of propagation attenuation plus shadowing, which can be approximated by the Gaussian mixture model (GMM) with all system parameters, is fully determined by our newly defined metric 10/\ln 10\beta /\sigma s , namely, the attenuation exponent $\beta$ to standard deviation of shadowing \sigma _{s} ratio (ASR). The convolution of GMM and antenna loss statistics is elaborately transformed to a series of differential equations. A closed-form pdf of large-scale path losses with sectorized antenna pattern can be obtained by solving these differential equations. To reduce the computational complexity, we further prove that the exciting sources of these differential equations can be tightly approximated by weighted Gaussian functions, and thus, the final solutions (i.e., pdf of path losses) can be derived in the form of Gaussian and Dawson functions. Our analytical results are verified by extensive numerical computation and Monte Carlo simulation results, e.g., the impact of ASR on the shape of pdf of propagation attenuation plus shadowing. Compared with traditional Gaussian-fitting approach, our newly derived pdf of large-scale path losses with sectorized antenna patterns is at least two orders of magnitude more accurate in terms of Kullback–Leibler divergence under typical propagation attenuation and shadowing conditions. [ABSTRACT FROM AUTHOR]

The statistical characteristics of the signal-to-interference plus noise ratio (SINR) are closely related to many performance metrics of cellular networks. In this paper, the downlink average rate and SINR distribution are studied for orthogonal frequency division multiple access (OFDMA)-based cellular networks subject to the distance-dependent path loss and shadow fading (SF). With the analytical approximate mean and moment generating function (MGF) of the SINR in the logarithmic domain, the closed-form approximation for the lower and upper bounds of the average rate is obtained. Then the distribution of the SINR in the logarithmic domain is proposed to be approximated as the normal inverse Gaussian (NIG) distribution whose parameters are computed explicitly through moment matching. Also, the closed-form expression for the cumulative distribution function (CDF) of the SINR based on the NIG approximation is derived. Simulation results not only verify the tightness of the bounds, but also show that the NIG approximation is up to one order of magnitude more accurate than the Pearson type IV approximation and at least one order of magnitude more accurate than the lognormal approximation when the SF correlation coefficient is small or the standard deviations of the SF are large or different. [ABSTRACT FROM AUTHOR]

We demonstrate a high refractive index (RI) liquid level sensor based on coreless multimode fiber (CMF) which is capable of measuring the liquid level and discriminating the high RI. The direct exposure of the CMF enables a strong interaction between the high-order modes guided in it and the surrounding medium through evanescent wave. Part of the energy leak out at the fiber/liquid interface when the RI of the liquid exceeds that of the CMF. The transmission of the single-mode fiber (SMF)-CMF-SMF structure is a function of both the liquid level and RI which experiences leakage loss with the increasing liquid level. Liquid level information can be determined by simply selecting a wavelength range with linear power variation. The proposed sensor with 4.1-cm CMF has approximately linear responses of −0.223, −0.253, −0.316, −0.392, and −0.461 dB/mm for glycerol solution concentrations of 98%, 96%, 92%, 88%, and 84% in a 2-nm wavelength range, respectively. Such a simple and low-cost sensor may be integrated as biochemical probes, indicating preferable sensing performance and practicability. [ABSTRACT FROM PUBLISHER]