Insulation resistance degradation models of extruded power cables under thermal ageing

Insulation resistance (IR) is an essential metric indicating insulation conditions of extruded power cables. To deliver reliable IR simulation as a reference for practical cable inspection, in this paper, four IR degradation models for cross-linked polyethylene-insulated cables under thermal ageing are presented. In addition, the influences of methodologies and temperature profiles on IR simulation are evaluated. Cable cylindrical insulation is first divided into sufficiently small segments whose temperatures are simulated by jointly using a finite volume method and an artificial neural network to model the thermal ageing experiment conditions. The thermal degradation of IR is then simulated by dichotomy models that randomly sample fully degraded segments based on an overall insulation (layer) ageing condition estimation and discretization models that estimate the gradual degradation of individual segments, respectively. Furthermore, uniform and non-uniform temperature profiles are incorporated into dichotomy and discretization models, respectively, for a comparison. The IR simulation results are not only compared between different models, but also discussed around the sensitivity of IR simulation to segment sizes and degradation rates. This provides cable assessment engineers with insights into model behaviour as a reference for their selection of appropriate IR degradation models

Pengembangan Media Pembelajaran Fisika Berupa Buletin Dalam Bentuk Buku Saku Untuk Pembelajaran Fisikakelas VIII Materi Gaya Ditinjau Dari Minat Baca Siswa

Tujuan dari penelitian ini untuk mengembangkan media pembelajaran berupa buletin dalam bentuk buku saku untuk pembelajaran Fisika kelas VIII pada materi Gaya ditinjau dari aspek materi, konstruk, dan bahasa serta minat baca siswa. Penelitian ini termasuk penelitian pengembangan yang menggunakan metode Research and Development (R&D). Penelitian ini menggunakan model pengembangan model prosedural yaitu model yang bersifat deskriptif yang menunjukkan tahapan-tahapan yang harus diikuti untuk menghasilkan produk berupa media pembelajaran.Jenis data yang diperoleh bersifat kualitatif dan kuantitatif yaitu angket dan wawancara. Teknik analisis data yang digunakan adalah analisis deskriptif kualitatif dan kuantitatif. Hasil penelitian menunjukkan bahwa media pembelajaran yang dikembangkan berupa buletin Fisika dalam bentuk buku saku memiliki kriteria sangat baik berdasarkan penilaian dari ahli materi, ahli bahasa Indonesia, dan ahli media memberikan rata-rata penilaian sebesar 86,56%. Media pembelajaran yang dikembangkan juga memiliki kriteria sangat baik bila ditinjau dari peningkatan minat baca siswa. Hal ini terbukti pada hasil angket minat baca awal dan akhir yang diberikan kepada siswa yang memberikan rata-rata peningkatan sebesar 11,13%. Selain itu juga dianalisis dengan menggunakan uji-t berpasangan terhadap data masing-masing kelompok uji coba untuk mengetahui signifikansi dari peningkatan minat baca siswa. Untuk uji coba perorangan diperoleh hasil perhitungan thitung = 6,957 > ttabel = 1,943 dan nilai Sig. = 0,001 < 0,05 yang berarti sangat signifikan. Untuk kelompok kecil didapatkan hasil perhitungan bahwa thitung = 7,848 > ttabel = 1,725 dan nilai Sig. = 0,000 < 0,05 yang berarti sangat signifikan. Untuk kelompok besar juga didapatkan hasil perhitungan bahwa thitung = 20,214 > ttabel = 1,725 dan nilai Sig. = 0,000 < 0,05 yang berarti sangat signifikan. Simpulan dari penelitian ini adalah media pembelajaran berupa buletin dalam bentuk buku saku memiliki kriteria sangat baik bila ditinjau dari aspek materi, konstruk, dan bahasa serta minat baca siswa

XLPE cable insulation resistance modelling under annealing and thermal ageing effects

Cross-linked polyethylene (XLPE) insulated electrical cables are widely deployed for electricity transmission due to the reliable thermomechanical performance and excellent electrical dielectric properties of XLPE insulation. Insulation resistance (IR) is a common metric indicating the electrical condition of cable insulation that undergoes annealing and thermal ageing over its service life. Most research related to the IR simulation deals with either the thermal ageing process of XLPE insulation itself or the annealing process of XLPE insulation by considering the diffusion of chemical specifies from semicon layers. This paper develops a discretisation IR model to estimate the temperature distribution across the XLPE insulation layer and simulate the IR drop under the thermal ageing effect or the U-shape variation of IR under the joint effects of annealing and thermal ageing, respectively. The IR simulation results are discussed around the necessity of combining annealing and thermal ageing effects for IR simulation with the presence of semicon layers

Insulation Resistance Degradation Models of Extruded Power Cables under Thermal Ageing

Insulation resistance (IR) is an essential metric indicating insulation conditions of extruded power cables. To deliver reliable IR simulation as a reference for practical cable inspection, in this paper, four IR degradation models for cross-linked polyethylene-insulated cables under thermal ageing are presented. In addition, the influences of methodologies and temperature profiles on IR simulation are evaluated. Cable cylindrical insulation is first divided into sufficiently small segments whose temperatures are simulated by jointly using a finite volume method and an artificial neural network to model the thermal ageing experiment conditions. The thermal degradation of IR is then simulated by dichotomy models that randomly sample fully degraded segments based on an overall insulation (layer) ageing condition estimation and discretization models that estimate the gradual degradation of individual segments, respectively. Furthermore, uniform and non-uniform temperature profiles are incorporated into dichotomy and discretization models, respectively, for a comparison. The IR simulation results are not only compared between different models, but also discussed around the sensitivity of IR simulation to segment sizes and degradation rates. This provides cable assessment engineers with insights into model behaviour as a reference for their selection of appropriate IR degradation models

Insulation resistance measurements of medium-voltage cross-linked polyethylene cables under thermal stresses

The insulation of medium-voltage electrical cables is usually composed of polymers such as cross-linked polyethylene (XLPE) that excel in electrical dielectric properties and thermomechanical reliability. Thermal stress is one of the key factors that degrade the insulation performance of heavily loaded cables and eventually cause irreversible cable failures. To inform XLPE insulation resistance (IR) changes which measure cable insulation conditions under thermal stresses and assist in the development of related IR models, this paper presents IR measurements of 10 kV XLPE power cables which were thermally aged at around 100 oC under an accelerated thermal ageing experiment. The yearlong IR observations exhibited two consecutive U-shape changes followed by a rough decline, which might reflect a joint effect of annealing and thermal ageing. The experiment results highlight the necessity of enhancing IR models to additionally consider the promotion of hopping conduction within insulation by the chemical components diffused from semicon layers under the annealing effects

Modulation Mechanism of Acoustic Scattering in Underwater Corner Reflectors with Acoustic Metasurfaces

Using the tunderwater corner reflector (CR) to simulate the acoustic scattering characteristics of the military target is a new technology to counter active sonar detection. Existing underwater CRs only have the ability to interfere with the acoustic field, but have limitations in acoustic wave modulation. Therefore, acoustic metasurfaces applied on CRs to enhance the ability of acoustic wave modulation has a great application prospect. A fast prediction method based on the Kirchhoff approximation (KA) and the ray tracing theory is proposed to calculate the acoustic scattering characteristics of CR with acoustic metasurfaces in grooves array type. The accuracy of the method is verified by the finite element method (FEM) simulation. The modulation effect of CR with grooves array in different gradient combinations on the structural scattering acoustic field is analyzed. The research shows that the CR with different combinations of the acoustic metasurface has an obvious modulation effect on the amplitude of the acoustic waves and the deflection of acoustic field. In particular, the grooves array in combination with positive and negative gradients has an obvious deflection impact on the scattering acoustic field

Study on the scattered sound modulation with a programmable chessboard device

Metasurfaces open up unprecedented potential for applications in acoustic deflection. Achieving adaptive control of a scattered sound field (SSF) using a flexible metasurface structure is of great scientific interest. However, as the conventional finite element method (FEM) is limited by computational efficiency, it is necessary to develop a fast and accurate method to predict the SSF. In this work, we design a chessboard device with an array of square grooves for the modulation of SSF and develop a fast calculation method for 3D SSF using a Kirchhoff approximation phase correction. Several SSF spatial modulations obtained using the chessboard model are computed with a fast algorithm. In addition, an experimental test-case in a semi-anechoic chamber, contrasted and analyzed scattered acoustic pressure using FEM, is designed to regulate the SSF performance of the chessboard device. Field measurements obtained show that the spatial directivity of chessboard device can be modified by artificially programming the phase or depth distribution of the groove array. The chessboard device and associated fast calculation method lend themselves to applications in the acoustic stealth of targets in air or water

Answering XML Twig Queries with Automata

XML is emerging as a de facto standard for information representation and data exchange over the web. Evaluation of twig queries, which allows users to find all occurrence of a multiple branch pattern in an XML database, is a core and complicate operation for XML query processing. Performance of conventional evaluation approaches based on structural join declines with the expansion of data size and query complexity

Developments in target micro-doppler signatures analysis: radar imaging, ultrasound and through-the-wall radar

Target motions, other than the main bulk translation of the target, induce Doppler modulations around the main Doppler shift that form what is commonly called a target micro-Doppler signature. Radar micro-Doppler signatures are generally both target and action speci c and hence can be used to classify and recognise targets as well as to identify possible threats. In recent years, research into the use of micro-Doppler signatures for target classi cation to address many defence and security challenges has been of increasing interest. In this paper, we present a review of the work published in the last 10 years on emerging applications of radar target analysis using micro-Doppler signatures. Speci cally we review micro-Doppler target signatures in bistatic SAR and ISAR, through-the-wall radar and ultrasound radar. This article has been compiled to provide radar practitioners with a unique reference source covering the latest developments in micro-Doppler analysis, extraction and mitigation techniques. The paper shows that this research area is highly active and fast moving and demonstrates that micro-Doppler techniques can provide important solutions to many radar target classification challenges