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Abstract The main part of oil‐immersed power equipment is oil‐paper insulation. At lower ambient temperatures, transformer oil will become viscous. As a result, compared to those at room temperature or operating temperature, the frequency domain dielectric properties of oil‐paper insulation at low temperatures are drastically different. For evaluating the insulation condition of electrical equipment, it is essential to accurately determine their dielectric properties. This paper described the FDS test, the DC conductivity test, and the transformer oil viscosity test, which was carried out in a laboratory environment for different ageing of oil‐immersed pressboard and transformer oil at 233–373 K. The effects of temperature on the dielectric properties at the competing mechanisms of polarisation and conductivity loss were clarified based on variations of the FDS curves. Considering the viscosity change of ageing transformer oil at low temperatures, the Arrhenius and VFT viscosity equations were used to achieve a fitting calculation in the different temperature zones. Based on the molecular/ion transition model in the force field and electric field, the characterisation relationships between the dynamic viscosity, DC conductivity, and test temperature of transformer oil were established. The limitations of conventional transformer oil equivalent dielectric relaxation models over a wide temperature range were finally clarified by combining the test findings of the DC conductivity over a wide temperature range with observed and simulated calculations. This paper provides an essential theoretical reference when using the FDS test to diagnose the insulation performance of oil‐immersed power equipment in extremely cold regions.

Epoxy/glass fibre composites possess excellent mechanical and electrical properties and are widely utilised in electrical and electronic power equipment. However, the composites exhibit relatively poor thermal conductivity, causing the temperature of the composites to increase during the operation of power equipment, resulting in a significant reduction in the electrical breakdown strength. Although the effects of thermal aging on polymeric materials have been widely studied, its influence on electrical strength mechanisms has not been investigated at the molecular level. In this study, epoxy/glass fibre composite specimens were subjected to accelerated thermal aging treatment for 360 h at 180 °C. Functional groups, molecular chain dynamics, and electrical breakdown are characterised using infrared spectroscopy, dielectric spectroscopy, and breakdown measurement. Subsequently, electrical breakdown mechanism and life prediction of the thermally aged composites are discussed. During thermal aging, the epoxy resin molecular chains undergo continuous oxidation and chain scission, which generate numerous polar functional groups and short chains and an increase in the free volume. This triggers an enhancement in the chain segmental dynamics, thereby significantly reducing the activation energy of the epoxy resin. After 360 h, activation energy decreased from 0.78 eV to 0.67 eV. The DC breakdown voltages of the specimens decreased from 168.28 kV/mm to 134.91 kV/mm. An insulation life prediction model for thermally aged epoxy/glass fibre composites is established based on the time-temperature equivalence theory. The prediction results indicate that the service life of the operational composites is approximately 11.2 years at 353 K, which is consistent with engineering experience.

In this work, a day-ahead dispatch optimization model with energy-type, power-type, and composite-type energy storage systems (ESSs) is established to participate in multiple frequency control ancillary services (FCASs), in wind-energy-integrated power systems. This model is designed to better handle the operational uncertainties of wind energy, mitigate operational risks and reduce carbon emissions. Leveraging the complementary features of different types of ESSs, the proposed operation strategies of regulation units can respond to multiple FCASs and achieve the optimal task allocation among different types of resources. Various uncertainty handling approaches are adopted to better cope with the randomness of step disturbances and wind power fluctuations. Furthermore, a new environmental factor is devised in the dispatch objective and the time-of-use carbon-price carbon emission trading (ToU-CET) and ladder-type CET (LT-CET) models are developed. They can incorporate dynamic carbon prices and leverage mechanisms to reduce carbon emissions during daily operations. The effectiveness of the proposed model is verified by case studies, and the decisions can help save energy and reduce carbon emissions in modern power systems with wind power generators with high security and reliability.

This is is an article in the field of mineral processing engineering. In this study, the controllable factors such as the amount of collector used in the flotation, the amount of foaming agent, the ore feeding rate and the aeration amount were changed,we conducted a column flotation comparative test study on fine coal with or without nanobubbles. On this basis, the recovery mechanism of nano-bubble to fine coal was expounded. The test results show that nano-bubbles can improve the recovery rate of ultra-fine coal particles, save about 1/2 of the dosage of the agent under the same ash content, and play the role of the second collector. In addition, the use of nanobubble flotation can still obtain a better sorting index under the condition of lower airflow velocity. Nanobubbles can be preferentially adsorbed on the surface of hydrophobic particles to make fine-grained coal agglomerate into larger particles, enhancing the collision probability of conventional bubbles and coal particles to achieve the effect of enhanced flotation.

Taking the aggregator as a unit, battery swapping and charging stations (BSCSs) for electric vehicles (EVs) can be aggregated and dispatched by grid operators, to realize the demand-side resource regulation. Considering the characteristics of an aggregator’s multilateral services, in this study, BSCSs need to ensure the quality of swapping service for EV users and participate in the demand-side regulation response. Firstly, we analyze the operation mechanism of a BSCS in the aggregation mode and propose a state transition model for EV batteries. On this basis, the EV demand uncertainty is incorporated by a distributed robust optimization (DRO) approach for multi-timescale inventories, and an optimization model to maximize the BSCSs’ income is established, which obtains the optimal load planning and dispatchable capacity scheduling for a BSCS aggregator. Extensive simulations and numerical results show that the BSCS aggregator with demand-side regulation capacity can increase its income by 59.05% and 36.78% on working and non-working days, respectively. Also, the aggregator does not worsen the original power load while meeting the EV swapping demand and can decrease the daily load fluctuations by 0.65% and 12.89%, reduce the peak–valley difference by 5.81% and 7.80%, and increase the load rate by 3.67% and 4.08% in working and non-working day situations through providing the dynamic dispatchable capacity for the grid.

Abstract The converter transformer is an essential part of the DC transmission system. Compared with the traditional oil‐impregnated AC transformer, the main insulation of the converter transformer bears more complex electric field aging stress during long‐term operation. The influence of the proportion of AC components in the AC/DC composite electric field on insulation aging is still unclear. Therefore, a combined aging test platform of composite electric field and thermal was built in the laboratory, and accelerated aging tests of oil‐paper insulation under different AC/DC ratios were carried out. Through the time‐frequency domain dielectric response characteristics of oil‐paper insulation, the quantitative relationship between the time‐frequency domain dielectric response characteristic parameters and AC proportional coefficient in different aging stages was obtained. The results show that the influence of the AC component on the aging of the oil‐impregnated pressboard is more prominent. The maximum relaxation polarization time and the maximum exponential coefficient of polarization–depolarization current (PDC) can effectively characterize the aging of oil‐paper insulation. Meanwhile, to accurately assess the insulation state of the converter transformer, this paper established the equivalent dielectric relaxation model for the main insulation structure. A quantitative assessment method for moisture content and aging of oil‐paper insulation based on time‐frequency domain dielectric response was proposed. The influence of transformer oil conductivity, test temperature, and main insulation structure was eliminated. The effectiveness of this method was verified by comparative tests, the maximum error for DP is 20, and the maximum error for moisture content is 0.15%. The research results of this paper can provide theoretical support for on‐site assessment of converter transformer insulation status.

Single-phase-to-ground fault in low-current grounding systems represents a serious public safety concern. Low-voltage (LV) sensors, with their growing maturity, can now monitor multiple points of the mid-voltage (MV) distribution network. This paper proposes a new method for identifying single-phase-to-ground line faults and locating them using LV sensors deployed on the LV side of distribution transformers. We analyze the characteristics of the negative-sequence signal on the LV side after a single-phase grounding fault occurs on the MV side. The negative-sequence current can distinguish between fault and non-fault lines. By setting the ratio coefficient of negative-sequence voltage and positive-sequence voltage, we can use multi-point collaborative calculation and comparison to determine the section of the fault point. We consider the unbalanced load on the LV side and the special case of a fault point on one end of the line. Through simulation of combined MV and LV distribution systems in MATLAB software and dynamic model experiments, we verify that the proposed method has good robustness and accuracy. Monitoring the status information of the MV distribution network through LV sensors has great potential in practical application and implementation for realizing the fault detection of low-current grounding systems.

Pre-separation test of grinding-high intensity magnetic separation-medium magnetic separation was carried out on the flotation tailings of Gongchangling hematite. The iron grade of magnetic separation rough concentrate obtained by pre-separation is 41.71%，yield is 33.62% and iron recovery is 84.21%. The effects of two flotation processes, flotation column and flotation machine roughing, on the quality improvement of pre-concentration coarse concentrate were compared. The single factor test results show that the optimal working parameters of flotation column are feeding pressure 0.08 Mpa and aeration 0.05 m3/h. Through the closed-circuit test of one roughing, one cleaning and one scavenging process made of flotation column and two flotation units，the technical indexes of 18.89% concentrate mineral rate, 65.29% grade and 74.07% iron recovery can be obtained, which are 0.27 percentage points and 2.61 percentage points higher than that of single flotation machine process, respectively.

Flavonoids are important bioactive components in Dendrobium officinale, a medicinal orchid. They are involved in many biological activities, including protecting plants against biotic and abiotic stresses. Research on the key genes related to flavonoid biosynthesis in D. officinale is limited. In this study, one of the key flavonoid biosynthesis genes, flavanone 3-hydroxylase (F3H), was characterized from D. officinale. The open reading frame of DoF3H was 1 134 bp long and it encoded a 377-amino acid protein. The DoF3H protein showed considerably high homology with F3H proteins from other plant species and shared a common evolutionary ancestor with other F3Hs. DoF3H transcripts were detected in different organs of adult plants and mainly accumulated in flowers, followed by roots, stems and leaves, a pattern that was similar to the content of flavonoids. Recombinant DoF3H protein, which was localized in the cytosol, could convert naringenin to dihydrokaempferol. The mRNA levels of DoF3H were significantly induced by salt and cold stresses. Furthermore, the heterologous expression of DoF3H in Escherichia coli conferred it higher tolerance to salt and cold stresses. These results provide insight into the molecular function of DoF3H in the biosynthesis of flavonoids, and provide a new application for improvement of abiotic tolerance in D. officinale.

Abstract The stable operation of transformers is an important guarantee of power system security. The temperature distribution of main insulation is different in long‐term operation. The temperature difference between the local hottest spot temperature and the average oil temperature in the transformer exceeds 30 K. Therefore, the oil‐paper insulation inside the transformer will exhibit non‐uniform ageing after long‐term operation. At present, frequency domain dielectric response (FDS) technology is widely used in transformer ageing assessment. However, the existing assessment methods are only used for overall insulation ageing assessment. The average moisture content and polymerization degree of the overall insulation between each phase winding are obtained. But it still cannot be used to assess the non‐uniform ageing of the transformer's main insulation. The radial, axial, and two directions non‐uniform ageing models have been made in the laboratory in this study. The FDS and physicochemical properties of non‐uniform ageing models were tested. The variation law of FDS for non‐uniform ageing models was analysed. Meanwhile, the dielectric relaxation model of non‐uniform ageing for main insulation was established. The method of frequency division iterative calculation was proposed. Combined with the Fessler moisture balance formula of ageing oil‐paper insulation, the quantitative assessment method for ageing parameters of the non‐uniform ageing model can be realized. Compared the calculated results with the chemical analysis results, the relative error of the polymerization degree calculation is less than 4%, and the error of the moisture content calculation is less than 0.3%. The calculation results can meet the needs of the engineering apply. Therefore, this method can realize the quantitative assessment of transformer main insulation ageing, which is of great significance to assess the transformer insulation state.

Network RTK (NRTK), one of the primary means of high-precision real-time kinematic positioning (RTK), has been widely used. The key to providing highly accurate positioning is the ambiguity of the reference station being correctly fixed, but the atmospheric errors must be handled carefully, which seriously affects the efficiency of ambiguity fixing. This paper aims to improve the efficiency of ambiguity fixing by studying the time-varying characteristics of atmospheric errors. Once reasonable constraints are imposed on atmospheric parameters in the uncombined observation model, it can better fix ambiguity. Atmospheric parameters are estimated by random walk at the reference station, and the power spectral density (PSD) of atmosphere is determined by real-time observations, instead of using empirical values or empirical models that do not consider atmospheric variations. The experimental results showed that the real-time estimated PSD can improve the ambiguity fixing time by 18.4% and the ambiguity fixing success rate for the reference station by 11.7%, compared with using empirical PSD for atmospheric parameters. Unlike general NRTK positioning based on differential error correction values, undifferenced NRTK estimates the integer ambiguity and undifferenced error correction value at a single reference station, ensuring the independence of the error correction value of each reference station, and it can be easily broadcast and received through the network, which is more convenient for realizing high-precision RTK positioning for users.

Dendrobium officinale is a precious medicinal Chinese herb that employs facultative crassulacean acid metabolism (CAM) and has a high degree of abiotic stress tolerance, but the molecular mechanism underlying the response of this orchid to abiotic stresses is poorly understood. In this study, we analyzed the root microstructure of D. officinale plantlets and verified the presence of chloroplasts by transmission electron microscopy. To obtain a more comprehensive overview of the molecular mechanism underlying their tolerance to abiotic stress, we performed whole‐transcriptome sequencing of the roots of 10-month-old plantlets exposed to salt (NaCl) treatment in a time‐course experiment (0, 4 and 12 h). The total of 7376 differentially expressed genes that were identified were grouped into three clusters (P < 0.05). Metabolic pathway analysis revealed that the expression of genes related to hormone (such as auxins, cytokinins, abscisic acid, ethylene and jasmonic acid) biosynthesis and response, as well as the expression of genes related to photosynthesis, amino acid and flavonoid metabolism, and the SOS pathway, were either up- or down-regulated after salt treatment. Additionally, we identified an up-regulated WRKY transcription factor, DoWRKY69, whose ectopic expression in Arabidopsis promoted seed germination under salt tress. Collectively, our findings provide a greater understanding of the salt stress response mechanisms in the roots of a facultative CAM plant. A number of candidate genes that were discovered may help plants to cope with salt stress when introduced via genetic engineering.

Multi Global Navigation Satellite System (GNSS) Precise Point Positioning (PPP) has become the mainstream of PPP technology. Due to the differences in the coordinates and time references of each GNSS, multi-GNSS PPP must include additional Inter-System Bias (ISB) parameters to ensure compatibility between different GNSSs. Therefore, research on the characteristics of ISB is also essential. To analyze the short- and long-term time characteristics of multi-GNSS ISBs, as well as their relationship with receiver type and receiver antenna type, the Undifferenced and Uncombined (UDUC) PPP model of Global Positioning System (GPS), BeiDou navigation satellite system (BDS), and Galileo satellite navigation system (Galileo) was rigorously derived, and the physical of ISBs was elaborated in depth. ISB parameters were estimated and analyzed using 31 days of data from the 31 Multi-GNSS Experimental stations (MGEX). The results indicate that: (1) the ISB value is dependent on the station receiver type, receiver antenna type, analysis center product utilized, and GNSS system. (2) The short-term time characteristics of ISB-COM, ISB-WUM, and ISB-GBM are similar for the same station but not for the long term. In addition, ISBs are more stable in the short term. (3) There is little correlation between the ISB time characteristics, the receiver type, and the receiver antenna type, and the day-boundary discontinuity(DBD) on the ISB can be ignored for the concussive days’ process.

Abstract Background DNA methylation is a conserved and important epigenetic modification involved in the regulation of numerous biological processes, including plant development, secondary metabolism, and response to stresses. However, no information is available regarding the identification of cytosine-5 DNA methyltransferase (C5-MTase) and DNA demethylase (dMTase) genes in the orchid Dendrobium officinale. Results In this study, we performed a genome-wide analysis of DoC5-MTase and DodMTase gene families in D. officinale. Integrated analysis of conserved motifs, gene structures and phylogenetic analysis showed that eight DoC5-MTases were divided into four subfamilies (DoCMT, DoDNMT, DoDRM, DoMET) while three DodMTases were divided into two subfamilies (DoDML3, DoROS1). Multiple cis-acting elements, especially stress-responsive and hormone-responsive ones, were found in the promoter region of DoC5-MTase and DodMTase genes. Furthermore, we investigated the expression profiles of DoC5-MTase and DodMTase in 10 different tissues, as well as their transcript abundance under abiotic stresses (cold and drought) and at the seedling stage, in protocorm-like bodies, shoots, and plantlets. Interestingly, most DoC5-MTases were downregulated whereas DodMTases were upregulated by cold stress. At the seedling stage, DoC5-MTase expression decreased as growth proceeded, but DodMTase expression increased. Conclusions These results provide a basis for elucidating the role of DoC5-MTase and DodMTase in secondary metabolite production and responses to abiotic stresses in D. officinale.

To achieve optimal configuration of switching devices in a power distribution system, this paper proposes a repulsive firefly algorithm-based optimal switching device placement method. In this method, the influence of territorial repulsion during firefly courtship is considered. The algorithm is practically applied to optimize the position and quantity of switching devices, while avoiding its convergence to the local optimal solution. The experimental simulation results have showed that the proposed repulsive firefly algorithm is feasible and effective, with satisfying global search capability and convergence speed, holding potential applications in setting value calculation of relay protection and distribution network automation control. Keywords: Power distribution systems, Switching device, Repulsive firefly algorithm, Optimal placement, Reliability

The APETALA2 (AP2) transcription factors (TFs) play crucial roles in regulating development in plants. However, a comprehensive analysis of the AP2 family members in a valuable Chinese herbal orchid, Dendrobium officinale, or in other orchids, is limited. In this study, the 14 DoAP2 TFs that were identified from the D. officinale genome and named DoAP2-1 to DoAP2-14 were divided into three clades: euAP2, euANT, and basalANT. The promoters of all DoAP2 genes contained cis-regulatory elements related to plant development and also responsive to plant hormones and stress. qRT-PCR analysis showed the abundant expression of DoAP2-2, DoAP2-5, DoAP2-7, DoAP2-8 and DoAP2-12 genes in protocorm-like bodies (PLBs), while DoAP2-3, DoAP2-4, DoAP2-6, DoAP2-9, DoAP2-10 and DoAP2-11 expression was strong in plantlets. In addition, the expression of some DoAP2 genes was down-regulated during flower development. These results suggest that DoAP2 genes may play roles in plant regeneration and flower development in D. officinale. Four DoAP2 genes (DoAP2-1 from euAP2, DoAP2-2 from euANT, and DoAP2-6 and DoAP2-11 from basal ANT) were selected for further analyses. The transcriptional activation of DoAP2-1, DoAP2-2, DoAP2-6 and DoAP2-11 proteins, which were localized in the nucleus of Arabidopsis thaliana mesophyll protoplasts, was further analyzed by a dual-luciferase reporter gene system in Nicotiana benthamiana leaves. Our data showed that pBD-DoAP2-1, pBD-DoAP2-2, pBD-DoAP2-6 and pBD-DoAP2-11 significantly repressed the expression of the LUC reporter compared with the negative control (pBD), suggesting that these DoAP2 proteins may act as transcriptional repressors in the nucleus of plant cells. Our findings on AP2 genes in D. officinale shed light on the function of AP2 genes in this orchid and other plant species.

Dendrobium officinale Kimura et Migo is a precious traditional Chinese medicine. Despite D. officinale displaying a good salt-tolerance level, the yield and growth of D. officinale were impaired drastically by the increasing soil secondary salinization. The molecular mechanisms of D. officinale plants’ adaptation to salt stress are not well documented. Therefore, in the present study, D. officinale plants were treated with 250 mM NaCl. Transcriptome analysis showed that salt stress significantly altered various metabolic pathways, including phenylalanine metabolism, flavonoid biosynthesis, and α-linolenic acid metabolism, and significantly upregulated the mRNA expression levels of DoAOC, DoAOS, DoLOX2S, DoMFP, and DoOPR involved in the jasmonic acid (JA) biosynthesis pathway, as well as rutin synthesis genes involved in the flavonoid synthesis pathway. In addition, metabolomics analysis showed that salt stress induced the accumulation of some compounds in D. officinale leaves, especially flavonoids, sugars, and alkaloids, which may play an important role in salt-stress responses of leaf tissues from D. officinale. Moreover, salt stress could trigger JA biosynthesis, and JA may act as a signal molecule that promotes flavonoid biosynthesis in D. officinale leaves. To sum up, D. officinale plants adapted to salt stress by enhancing the biosynthesis of secondary metabolites.

Floral scent is a key ornamental trait that determines the quality and commercial value of orchids. Geraniol, an important volatile monoterpene in orchids that attracts pollinators, is also involved in responses to stresses but the geraniol synthase (GES) responsible for its synthesis in the medicinal orchid Dendrobium officinale has not yet been identified. In this study, three potential geraniol synthases were mined from the D. officinale genome. DoGES1, which was localized in chloroplasts, was characterized as a geraniol synthase. DoGES1 was highly expressed in flowers, especially in petals. DoGES1 transcript levels were high in the budding stage of D. officinale flowers at 11:00 a.m. DoGES1 catalyzed geraniol in vitro, and transient expression of DoGES1 in Nicotiana benthamiana leaves resulted in the accumulation of geraniol in vivo. These findings on DoGES1 advance our understanding of geraniol biosynthesis in orchids, and lay the basis for genetic modification of floral scent in D. officinale or in other ornamental orchids.

The acetylation or deacetylation of polysaccharides can influence their physical properties and biological activities. One main constituent of the edible medicinal orchid, Dendrobium officinale, is water-soluble polysaccharides (WSPs) with substituted O-acetyl groups. Both O-acetyl groups and WSPs show a similar trend in different organs, but the genes coding for enzymes that transfer acetyl groups to WSPs have not been identified. In this study, we report that REDUCED WALL ACETYLATION (RWA) proteins may act as acetyltransferases. Three DoRWA genes were identified, cloned, and sequenced. They were sensitive to abscisic acid (ABA), but there were no differences in germination rate and root length between wild type and 35S::DoRWA3 transgenic lines under ABA stress. Three DoRWA proteins were localized in the endoplasmic reticulum. DoRWA3 had relatively stronger transcript levels in organs where acetyl groups accumulated than DoRWA1 and DoRWA2, was co-expressed with polysaccharides synthetic genes, so it was considered as a candidate acetyltransferase gene. The level of acetylation of polysaccharides increased significantly in the seeds, leaves and stems of three 35S::DoRWA3 transgenic lines compared to wild type plants. These results indicate that DoRWA3 can transfer acetyl groups to polysaccharides and is a candidate protein to improve the biological activity of other edible and medicinal plants.

Improving the sodiophilicity of the substrate is essential to enhance the reversibility of anode-less sodium metal batteries. Here, we have prepared a sodiophilic nano-Pb coating on aluminum-based collectors by magnetron sputtering. The slow alloying kinetics between Pb and sodium allows prolonged Pb retention in the coating, endowing the coating with a durable sodiophilicity. [ABSTRACT FROM AUTHOR]