Search

Transformer insulation paper is a key indicator for transformer remaining operational life. Paper decomposition is evaluated using the degree of polymerization (DP) which calls for samples of insulation paper from operating transformers. Since collecting such paper samples is extremely difficult, other indicators have been used to indirectly reveal the DP value of insulation paper. This includes dissolved gases in transformer oil such as carbon oxides and hydrocarbon gases, furan compounds, methanol, ethanol, and moisture along with some oil characteristics such as interfacial tension. However, for the same oil sample, these individual parameters lead to different DP values. This is attributed to the lack of accuracy of the established mathematical and artificial intelligence models correlating DP with each of the above mentioned individual parameters. This paper presents a self-learning method to estimate the DP value of transformer insulation paper based on multiple transformer oil aging parameters. The proposed method comprises data processing, fuzzy c-means and linear regression. Results reveal that estimating the DP value based on multiple aging parameters is more accurate than estimating it using one single parameter as per the current practice. The proposed method not only helps to understand the correlation between multiple oil aging parameters and the DP value of paper insulation, but also promotes the establishment of more accurate life assessment models for power transformers based on these oil aging parameters.

In this communication, two polarization selective partial reflective decoupling layers (PRDLs) are utilized to mitigate at least two kinds of mutual couplings between two closely spaced dual-polarized dipole antennas. The PRDL is a large-scale model of an actual dielectric board, obtained by arranging a large number of identical conducting obstacles in a regular two-dimensional pattern. The two PRDLs are designed at proper distances from the antenna aperture with well-engineered dielectric constants for two preset polarizations. Each layer is selective to only one polarization by appropriately designing the dimension of the unit cells. Consequently, the two dominant couplings between the two dual-polarized antennas are reduced significantly. The measured isolation between all ports of the two antennas are increased to more than 21 dB, while their reflection coefficients can still maintain in satisfactory status. The radiation patterns, total efficiencies, and envelop correlation coefficients of the proposed antenna, as well as its counterpart without any decoupling measures, are also obtained through measurement, showing significant and reasonable improvements, which further indicates that it has great potential to be extended and applied to 5G MIMO arrays in both base stations and wireless routers. [ABSTRACT FROM AUTHOR]

In this communication, a circularly polarized (CP) dielectric resonator antenna (DRA) based on quasi-self-complementary metasurface (MS) has been proposed. Due to the quasi-self-complementary characteristic of the proposed MS, the phase difference of the transmission coefficients between two orthogonal linear polarizations is 90° in the frequency band from 25.5 to 26.5 GHz. The DRA with the proposed MS can realize the transformation from linear polarization to circular polarization at 25.6–25.99 GHz. The proposed MS significantly increases the gain and CP bandwidth of the DRA. The working bandwidth of the proposed antenna is included in the New Radio FR2 frequency band totally, which is considered as the follow-up expansion frequency of fifth-generation (5G) communication. The proposed MS-based antenna has realized the linear-to-circular polarization transformation in millimeter frequency band without additional substrate, which has not been researched yet. [ABSTRACT FROM AUTHOR]

A compact phased array with extended beam steering characteristics for the millimeter-waveband of the fifth-generation (5G) applications is presented in this communication. An E-shaped patch antenna placed on an electromagnetic bandgap ground (EBGG) with operating bandwidth of 24.2–27.5 GHz is used as the basic building block of the eight-element linear array. The array utilizes both the in-phase reflection characteristic for broad element radiation pattern and the bandgap characteristic for mutual coupling reduction for limited inter-element spacing of the proposed array. The existence of the EBGG enables a compact array with the inter-element spacing of around 0.4 wavelengths at the center frequency, yet the isolation between each element is still above 17 dB within the whole band of interest, which also helps to increase the array directivity at large scanning angles. The scanning angle of the array with the electromagnetic bandgap (EBG) structure ranges from −75° to 75° at 26 GHz within 3 dB scanning loss. The proposed EBGG extends the antenna array’s spatial coverage and enables a compact size of the array, which is very attractive for 5G millimeter-wave (mm-wave) application. [ABSTRACT FROM AUTHOR]

Reliability assessment is of crucial importance for power systems planning and operation. However, traditional reliability assessment methods mainly analyze electricity outages observed from the system side, regardless of whether end consumers are in need of electricity during such outage events. That is, they may not truly reflect actual impacts of various outages on consumers. To overcome this deficiency, a more precise consumer-centric spatiotemporal reliability assessment model is proposed for smart grid. Several new metrics are proposed to accurately evaluate the reliability level sensed by consumers, by considering actual interruption times of outages, consumers’ power consumption features, and load demand. Based on these new metrics, a method is proposed to quantitatively assess consumer-centric reliability compensation in the context of future power market. Furthermore, reliability and economy sensitive components that are key to improve consumer-centric reliability of systems are defined, detected, and analyzed, and a concise reward mechanism is established. The IEEE-RBTS distribution system is studied to illustrate the effectiveness and efficiency of the proposed models, metrics, and methods. [ABSTRACT FROM PUBLISHER]