Buildings near direct current transmission lines are sensitive to the electromagnetic environment, and the measurement of the electric field above them is important in engineering design and ...environmental assessment in China. The models of buildings and probes in the ion flow field were established to explore the accurate measurement method of the electric field above the building. Based on the upstream finite element method and the predictor–corrector method, the influence of whether the probe was grounded or not above the building was studied. On this basis, simulation experiments and real‐type experiments were carried out. The results show that when the electrical conductivity of the building was greater than 10−10 S/m, being grounded or not would not change the results. When the building conductivity was between 10−11 and 10−12 S/m, the electric field measurement results would be increased by 30% to 120% after grounding. In the real‐type experiments on the platform with a plywood roof, the relative error in the electric field when grounded or not was only 2.6%. This proved the reliability of the calculated results. In this paper, the measuring method of the DC space charge‐modified electric field above buildings was analyzed first, and the conclusion that ground wire can be cancelled above buildings with general materials was presented. The research results can provide a technical basis for the accurate measurement of the electric field above the buildings near DC transmission lines.
This paper studies how to use the field probe to measure the space charge‐modified electric field above the building, and proposes the measurement method of cancelling the ground wire.
Full text
Available for:
FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
As the miniaturization of electronic appliances and microprocessors progresses, low-permittivity interlayer materials are becoming increasingly important for their suppression of electronic ...crosstalk, signal propagation delay and loss, and so forth. Herein, a kind of copolyimide (CPI) film with a “fluorene” rigid conjugated structure was prepared successfully. By introducing 9,9-Bis(3-fluoro-4-aminophenyl) fluorene as the rigid conjugated structure monomer, a series of CPI films with different molecular weights were fabricated by in situ polymerization, which not only achieved the reduction of permittivity but also maintained excellent thermodynamic stability. Moreover, the hydrophobicity of the CPI film was also improved with the increasing conjugated structure fraction. The lowest permittivity reached 2.53 at 106 Hz, while the thermal decomposition temperature (Td5%) was up to 530 °C, and the tensile strength was ≥ 96 MPa. Thus, the CPI films are potential dielectric materials for microelectronic and insulation applications.
Full text
Available for:
IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
High voltage direct current (HVDC) transmission technology has incomparable advantages in long‐distance and large‐capacity transmission. With the development of HVDC transmission technology, ...transmission lines inevitably pass through some densely populated and economically developed areas. Due to environmental considerations, the space electric field around the buildings that are adjacent to HVDC transmission lines has aroused increasing attention. However, it is hard to be predicted by simulation because of the calculation complexity. This paper proposed a new calculated method to obtain the composite electric field around HVDC transmission lines with adjacent residential buildings, and the validity and correctness of the method are verified by the experimental results. Then, the distortion of the electric field around the building and its impact on the design of the safe corridor width of the HVDC transmission line is analyzed. The proposed method, unlike existing methods, can be used to predict the space composite electric field distribution around HVDC transmission lines and their adjacent residences, which are of arbitrary material, shape, and size. It can provide guide for the optimal design of transmission line corridors.
Full text
Available for:
FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
At high altitudes, the corona discharge around a conductor surface is severe, and the induced audible noise (AN) is irritating; this is due to the low air density at high altitudes. Therefore, AN has ...become a crucial limiting factor in the design of ac power lines of 500 kV or higher at high altitudes. An investigation of the spectral characteristics of AN should help provide a greater understanding of corona noise; however, only a few studies have investigated the spectral characteristics of AN in practical bundled conductors at high altitude. Therefore, it is difficult for power utility companies to select suitable conductors. In this study, the AN spectral characteristics of 6 × LGJ400, 6 × LGJ720, and 8 × LGJ500 bundled conductors were investigated using an ultra‐high‐voltage corona cage (8 × 8 × 35 m) in Xining, Qinghai Province (altitude: 2261 m). The AN equivalent A‐weighted level and the 1/3‐octave frequency characteristics of these three conductors were obtained, and the influence of the electric field (E‐field) on these characteristics was analysed. Subsequently, the relationship between the AN A‐weighted level and the 8‐kHz level was examined. We found that, with the increase of the E‐field, the low‐frequency components of AN level did not exhibit an obvious trend, but in the high‐frequency band (1.6–20 kHz), a clear positive correlation was observed between the spectrum level and E‐field strength. Among these three conductors, the 8 × LGJ500 conductor was the optimal conductor for reducing the AN levels at high altitude. The results obtained in this study can provide a data reference for the construction of high‐altitude ac power lines.
Full text
Available for:
FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The total electric field on the roof platform of buildings becomes a new and important indicator of the environmental assessment of HVDC projects. In this paper, the upper-stream finite element ...method is used to simulate and calculate the distribution characteristics of the total electric field on the roof platform of the flat-roofed building adjacent to an HVDC line, from the factors of material conductivity and three-dimensional structure. The results show that when the conductivity of the building is greater than 10
−10
S/m, it can be regarded as an equipotential body with the ground. Therefore, when the field mill measures the electric field on the roof platform, the field mill can be connected to the building to achieve the purpose of grounding. Otherwise, additional appropriate grounding treatment is required. Moreover, the protrusions such as parapets and stairwells on the roof platform of the building have both distortion and shielding effects on the total electric field. The larger the area of the protrusions, the better the shielding effect, making the total electric field on the roof platform weaker. Therefore, when measuring the total electric field on the roof platform, to avoid the unpredictability of the measurement results of the field mill, the field mill should be arranged in the center flat area at least 2 m away from the protrusions.
Corona loss is the key parameter for evaluating operating economy of ultra-high voltage (UHV) and extra-high voltage (EHV) alternating current (AC) transmission lines and is one of important factors ...that need to be considered in line design and operation. At present, corona losses of 8 × LGJ-630 conductors, which are commonly used in ultra-high voltage alternating current (UHV AC) double-circuit transmission lines on the same tower, and 8 × LGJ-720, and 10 × LGJ-720 bundle conductors with a larger cross-section and more bundle number in high-altitude areas have not yet been studied. In the paper, the corona losses of the 8 × LGJ-630, 8 × LGJ-720, and 10 × LGJ-720 conductors were measured under conditions of dryness, artificial moderate rain, heavy rain and a wet conductor, based on the UHV corona cage built in Ping’an County, Xi’ning, China at an altitude of 2,200 m. By taking typical 1,000 kV UHV-AC double-circuit transmission lines on the same tower as an example, the electric field strengths on the surface of conductors in the corona cage and the actual lines were calculated. On this basis, the corona loss of the UHV-AC double-circuit transmission line in a high-altitude area was analyzed. The research results can provide data reference for constructing UHV transmission lines in high-altitude areas.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Abstract
A series of high‐performance linear and cross‐linked polyimide (PI) aerogels with different molecular structures have been successfully synthesised using the freeze‐drying process. In this ...study, the comprehensive regulation of microstructure, thermodynamic, thermal insulation and dielectric properties of PI aerogels are achieved by controlling the rigid/flexible structure and composition of polymerised monomers. The increase in rigidity of PI molecular structure could promote the formation of denser pores, which is beneficial to improve the thermodynamic and thermal insulation properties of aerogels. Notably, the cross‐linked PI aerogel prepared by introducing cross‐linking agent (tris(4‐aminophenyl) amine, TPA) into linear PI exhibits high thermal stability (
T
d
5%
> 560°C), excellent ultralow permittivity (
ε
r
= 1.31,
f
= 10
6
Hz) and good thermal insulation property (
k
= 0.056 W/m · K). This innovative strategy promotes the wider application of the cross‐linked polyimide aerogel in the field of integrated circuits and aerospace exploration.
Full text
Available for:
FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Film capacitors have widely been used in modern electrical/electronic equipment because of their high insulation property and high-power density. However, the traditional dielectric films suffered a ...high conduction loss under high temperature and electric field conditions, which leads to the depression of high temperature energy storage properties. Herein, sandwich-structured composite films using biaxially oriented polyethylene terephthalate (BOPET) as the outer layers were prepared to construct the interfacial barrier, which was beneficial for hindering the propagation of breakdown path. In addition, epoxy resin was applied as the adhesive inner layer to bind the outer layers up tightly, while the boron nitride nanosheets (BNNSs) in the inner layer further improved the breakdown strength of the film and inhibited the conduction loss, especially under high temperature and electric field conditions. The composite film with optimized BNNSs content had a high discharged energy density of 9.11 J/cm3 and a ultrahigh charge–discharge efficiency of 95% at 25 °C, while the values were 6.45 J/cm3 and 70% at 150 °C, respectively, of which both were much higher than those of pure BOPET. Thus, the sandwich-structure method points out a promising way of preparing dielectric films with excellent energy storage performances.
Thanks to the development of deep learning, various sound source separation networks have been proposed and made significant progress. However, the study on the underlying separation mechanisms is ...still in its infancy. In this study, deep networks are explained from the perspective of auditory perception mechanisms. For separating two arbitrary sound sources from monaural recordings, three different networks with different parameters are trained and achieve excellent performances. The networks’ output can obtain an average scale-invariant signal-to-distortion ratio improvement (SI-SDRi) higher than 10 dB, comparable with the human performance to separate natural sources. More importantly, the most intuitive principle—proximity—is explored through simultaneous and sequential organization experiments. Results show that regardless of network structures and parameters, the proximity principle is learned spontaneously by all networks. If components are proximate in frequency or time, they are not easily separated by networks. Moreover, the frequency resolution at low frequencies is better than at high frequencies. These behavior characteristics of all three networks are highly consistent with those of the human auditory system, which implies that the learned proximity principle is not accidental, but the optimal strategy selected by networks and humans when facing the same task. The emergence of the auditory-like separation mechanisms provides the possibility to develop a universal system that can be adapted to all sources and scenes.
PDF
