Yiyi Zhang

Yiyi Zhang
Guangxi University · Department of Electrical Engineering

Professor

About

1,150
Publications
326,865
Reads
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14,721
Citations
Citations since 2017
1080 Research Items
14221 Citations
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201720182019202020212022202301,0002,0003,0004,0005,000
201720182019202020212022202301,0002,0003,0004,0005,000
Introduction
Yiyi Zhang currently works at the Department of Electrical Engineering, Guangxi University. Yiyi does research in Electrical Engineering, Solid State Physics and Materials Physics. Their current project is '973 project'.

Publications

Publications (1,150)
Article
Full-text available
Engineering experience shows that for transformers with long service life and serious moisture exposure, the inter‐turn paper insulation inside the winding will precipitate bubbles under the condition of electric field and conductor heating, which will endanger the equipment insulation. In order to explore the influence factors of bubbles formation...
Article
Full-text available
The evaluation of the state of transformer oil-immersed insulation based on the traditional methods becomes unreliable due to the nonuniform aging effect. To address this issue, a novel model for accessing the aging information of transformer oil-immersed insulation at the hotspot is proposed. In this article, frequency-domain spectroscopy (FDS) is...
Article
Full-text available
The paper/oil system is the main component of transformer insulation. Indicator plays a vital role in assessing the aging condition of local hot spots of transformer insulation paper. The cellulosic insulating paper is mainly composed of cellobiose. This study uses the molecular dynamics method based on reactive force field (ReaxFF) to pyrolyze the...
Article
Full-text available
Cellulose insulation paper is the main component of oil‐paper insulation systems in oil‐immersed transformers. However, the poor thermal conductivity and thermal stability of the cellulose can lead to thermal ageing. It is critical to address this issue by improving the performance of cellulose, nano‐SiC‐modified cellulose models were established b...
Article
Under actual working conditions, the cable is subjected to electrical, thermal, and mechanical stresses, and its aging is nonuniform along the radial direction. To fully dig out the rich information hidden in the frequency-domain spectroscopy (FDS) to evaluate the nonuniform thermal aging state of cross-linked polyethylene (XLPE), based on the Diss...
Article
The spread of the global COVID-19 epidemic has resulted in significant shifts in electricity consumption compared to regular days. It is unknown if standard single-task, single-indicator load forecasting algorithms can accurately reflect COVID-19 load patterns. Power practitioners urgently want a simple, efficient, and accurate solution for anticip...
Article
Full-text available
Owing to its lack of crosslinking, polypropylene (PP) is considered an environmentally friendly alternative to crosslinked polyethylene as high-voltage direct current (HVDC) cable insulation. However, pure PP can accumulate space charges under a HVDC, and thus must be modified for use as an insulating material for HVDC cables. In this study, 4-meth...
Preprint
The globally booming renewable power industry has stimulated an unprecedented appetite for metals as key infrastructure components. Many economies with different endowments and technology levels participate in global renewable power value chains (RPVCs) at different production stages, making it difficult to tell who supplies metals for whose low-ca...
Preprint
To enhance the thermodynamic properties of insulating paper, nano-fibrillated cellulose (NFC) was used to dope cellulose. The mechanical strength and thermal stability of cellulose insulating paper with different NFC doping mass fractions were analyzed by molecular dynamics simulations and experiments, and the optimal doping ratio of NFC was determ...
Article
Full-text available
As the main insulation material of the power electronic transformer (PET), polyimide (PI) is easy to accumulate space charge under the continuous high-frequency pulse voltage, which will threaten the operation of PET and cause electric field distortion. At present, the microscopic mechanism of charge transport under high-frequency voltage is unclea...
Article
Full-text available
The rapid growth of photovoltaic installed capacity exacerbates the power management challenges faced by photovoltaic power stations, emphasizing the importance of accurate and stable photovoltaic generation forecasting. As a result, researchers conducted research and developed several photovoltaic power prediction models. However, many prediction...
Article
Full-text available
The ageing kinetic model is regarded as an effective tool to describe the degradation of transformer paper insulation. However, the temperature of the transformer winding is unevenly distributed, and the existing ageing kinetic models only depend on experimental data of accelerated thermal ageing at a constant temperature. Given this issue, this wo...
Article
Full-text available
The polarization information contained in the frequency-domain spectroscopy (FDS) could be utilised for characterising the ageing degree of transformer oil-immersed insulation. However, the polarization information will be obscured by its conductance effect, it is thus hard to analyse the polarization behaviour by using the traditional FDS techniqu...
Article
With China’s vast territory and high regional heterogeneity in the spatial energy and water resources distribution, provincial-level embodied energy (EE) and virtual water (VW) reallocation are critical to regional energy and water recourse management but unfortunately, remain far from completed. In this paper, considering the heterogeneity of ener...
Article
Full-text available
The predictive model of aging indicator based on intelligent algorithms has become an auxiliary method for the aging condition of transformer polymer insulation. However, most of the current research on the concentration prediction of aging products focuses on dissolved gases in oil, and the concentration prediction of alcohols in oil is ignored. A...
Article
Full-text available
The polarization/depolarization curve (PDC), which contains abundant insulation information, is widely used to evaluate the insulation condition of the cross-linked polyethylene (XLPE) cables. However, the insulation condition assessing the result of the XLPE cables is usually inaccurate using the PDC technology because the parameters of the curren...
Article
Full-text available
The traditional method for transformer moisture diagnosis is to establish empirical equations between feature parameters extracted from frequency domain spectroscopy (FDS) and the transformer’s moisture content. However, the established empirical equation may not be applicable to a novel testing environment, resulting in an unreliable evaluation re...
Article
The generation and distribution of furfural are significantly affected by moisture content in the insulating paper. However, the diffusion mechanism of furfural under moisture effect is not clear, hence, this study investigates the effect of moisture on the diffusion characteristics of furfural by combining macro experiment and micro molecular dyna...
Article
Affected by the new coronavirus (COVID-19) pandemic, global energy production and consumption have changed a lot. It is unknown whether conventional short-term load forecasting methods based on single-task, single-region, and conventional indicators can accurately capture the load pattern during the COVID-19 and should be carefully studied. In this...
Article
The space charge effect of transformer insulating paper will distort its internal electric field, and its space charge effect will be more prominent under extremely complex working conditions. At present, the micromechanism of charge transport and electric field distortion characteristics of paperboard are not clear under complex working conditions...
Article
Full-text available
Abstract The charge transport and accumulation in oil–paper can cause the insulation degradation. So far, the most widely used model to simulate space charge transport and accumulation is the bipolar charge transport (BCT) model, which can well simulate the space charge dynamics. However, there are two shortcomings in the algorithms for solving the...
Article
Internal temperature distribution of an oil-immersed transformer is not uniform, resulting in an axial moisture gradient. Thus, the internal insulating paper ages unevenly with the synergetic impact of temperature and moisture. To examine the aging characteristics and moisture dispersion mechanism of insulating paper in a nonuniform system. A discr...
Article
The conventional method is insufficient for determining the worst aging state of traction transformer oil-paper insulation due to the non-uniform aging. To address this issue, an extended relaxation distribution model based on multi-population immune algorithm (ERD-MPIA) is proposed. Current work collects frequency domain spectroscopy (FDS) on the...
Article
The applicability of existing single aging indicator-based lifespan prediction methods needs further improvement during different aging stages. Considering the aforementioned challenges, this work proposes a two-stage residual lifespan prediction model based on both methanol and furfural. Firstly, the changes in methanol and furfural contents in oi...
Article
The complex dielectric frequency response (DFR) behavior is established during the frequency-domain spectroscopy (FDS) test, the methods for extracting the feature parameters to distinguish the diverse response process as well as achieve the state analysis, still deserve variable attention. To address this, a combination of nondominated sorting gen...
Article
Frequency domain spectroscopy (FDS) is a nondestructive insulation test method that has been widely applied to the insulation evaluation of power transformers. However, a major shortcoming of conventional FDS is the long test duration. Existing studies on accelerated FDS tests suffer from a lack of accuracy and are difficult to apply to field testi...
Article
The moisture-dependent parameter in the aging kinetic model is inaccessible due to the fluctuation of moisture during the aging period of bushing insulation. This significantly restricts the adoption of aging kinetics-based approaches for predicting transformer bushing insulation lifespan. Given this issue, an improved aging kinetic model is propos...
Article
Alcohol indicators in oil are utilized to evaluate the aging status of transformer paper insulation. The fluctuation of alcohol concentration in insulating oil affects the accuracy of aging assessment. Low molecular acid (LMA) is a significant factor influencing the concentration of alcohol in insulating oil. However, the mechanism of LMA on alcoho...
Article
Health condition monitoring of insulators is one of the key factors to ensure a stable power supply. This article proposes an automated insulator surface condition analysis approach based on vision measurement and convolutional neural network (CNN). Specifically, we consider the condition analysis of insulators as an image multiclassification probl...
Article
The X model is a conventional tool of frequency domain spectroscopy (FDS) technology for assessing the insulation state of oil-impregnated paper (OIP) bushings. However, the accuracy and applicability of the X model are questionable because it overlooked the effect of non-uniform thermal ageing, and there are no models and mathematical formulas tha...
Article
Frequency-domain spectroscopy (FDS)-based methods are rarely reported for aging evaluation of nonuniform aged transformer insulation, in part due to the unavailability of the database. To address this issue, this work proposes an improved geometric model for constructing the FDS of oil–paper insulation under axial nonuniform aging. First, the mathe...
Article
Existing methods based on frequency domain spectroscopy (FDS) cannot address the non-uniform aging of transformer insulation induced by the temperature gradient. To solve this issue, the genetic algorithm (GA) and finite element method (FEM) are combined to obtain the aging information of insulation at the transformer high-temperature region via th...
Article
This paper investigated the variation law of methanol concentration in transformer oil caused by operational defects and hotspot temperature from 500 kV field transformers. The correlations between various operational defects and methanol in oil are explained in detail for the first time. It is observed that three types of operational defects such...
Article
Furfural content dissolved in transformer oil is affected by the furfural diffusion in oil-paper insulation. Previous studies focused on the effects of temperature and moisture on furfural diffusion, while the effect of formic acid on furfural is ignored. Given this, the effect of formic acid on the diffusion properties of furfural is studied in th...
Article
A growing body of evidence suggests that the ethanol dissolved in the oil can be used as an indicator to effectively monitor the aging behavior of insulating paper. In this study, thermal aging experiments are performed on oil-paper systems with different initial moisture contents and aging temperatures, and then a gas chromatography-mass spectrome...
Article
This work investigates which acid can mainly lead to the reduction of alcohols contents in insulating oil during transformer oil-paper insulation aging. In terms of the activation free energy barrier theory, the microscopic mechanisms for the preferential reactions of methanol and ethanol with formic, acetic, naphthenic and stearic acids are analyz...
Article
Full-text available
The heterocharge accumulated in the oil-paper insulation system of the converter transformer will enhance the local electric field and cause insulation deterioration. Numerical simulation is an effective method to analyze heterocharge. Currently, the numerical simulation of heterocharge is mainly based on the bipolar charge transport (BCT) model an...
Article
Accurate description of wind speed probability distribution is an essential part of wind farm planning and dispatching. The two-parameter Weibull distribution is mostly used to fit unimodal wind speed probability distribution, but it suffers from low fitting accuracy and insufficient applicability. To solve these issues of the Weibull distribution,...
Article
The furfural analysis is an effective method to evaluate the aging state of transformer cellulose insulation. However, the existing research on the furfural analysis mainly focuses on ‘oil-paper’ system, without considering the oil-paper-pressboard system. In fact, the mass of insulating pressboard occupies a large proportion in the transformer, an...
Article
Full-text available
The total/partial oil change treatment can affect the furfural partitioning in oil-paper-pressboard insulation, resulting in poor accuracy of furfural analysis. Moreover, due to the high cost of total oil change, partial oil change is more practical during transformer operation. This paper investigates the furfural partitioning in the oil-paper-pre...
Article
The spatial mismatch between energy resources and water resources has been widely concerned. Electricity trade drives virtual water flows from electricity production sides to consumption sides, which can aggravate or alleviate regional water scarcity. Investigating the historical evolution of virtual water transmission and its impacts on water scar...
Article
Full-text available
Abstract The accuracy and feasibility of the traditional XY model of transformer oil–paper insulation system are disputable since it ignored the effect of non‐uniform aging and conductance on dielectric response property. Given this issue, this work attempted to report a modified XY model to overcome these defects. The novelty of this work is in th...
Article
Full-text available
Abstract The low‐frequency polarisation information of oil‐paper insulation could be easily obscured by the conductance effect, and the contained polarisation information thus can not be readily extracted from the frequency domain spectroscopy (FDS). Given this issue, an alternative idea is reported to extract the low‐frequency polarisation informa...
Article
Oil change, as an effective method, could improve the performance of liquid insulation. However, due to the furfural loss in oil after the oil change, the aging assessment results of cellulose insulation based on the traditional furfural-degree of polymerization (DP) model is not accurate. Besides, the different oil/pressboard mass ratio of the tra...
Article
Furfural, as a typical chemical indicator, is used to evaluate the aging state of the cellulose insulation in the transformer. However, partial oil replacement will lead to the loss of furfural in oil and disturb the equilibrium distribution of furfural between oil and cellulose insulation, which could affect the evaluation results of the aging sta...
Article
Full-text available
Objective To explore the alternative medicine of the shortage-drugs in the emergency department,and pro• vide the evidence to establish the list of alternative drugs for the targeted shortage-drugs. Methods With the focus shortage drugs designated by the National Health Commission,the initial list of alternative drugs for shortage drugs in emergenc...
Article
Full-text available
Moisture accumulates with the growing aging progress of oil-paper insulation and further shorten the remaining life of the transformer. The frequency domain spectroscopy (FDS) technique can be employed to realize the moisture estimation. However, the moisture estimation results would be unreliable once the aging effect on FDS was ignored. Given thi...
Article
Full-text available
Frequency domain spectroscopy (FDS) technique is widely used for the aging evaluation of the transformer oil-paper insulation system. However, the typical ‘relaxation information’ of FDS data in low-frequency regions is seriously affected by both the electrode polarization effect and conductance effect, which often leads to an unsatisfactory aging...
Article
Full-text available
The influence of nonuniform aging has not been considered in the prediction of the frequency domain spectroscopy (FDS) of the transformer oil-paper insulation (OPI) when using the finite element method (FEM). Given this issue, the modified simulation model was constructed based on the XY model and FEM. In the current work, the dielectric response...
Article
Full-text available
Derived from our original nomogram study by using the risk variables from multivariable analyses in the derivation cohort of 1383 patients with extranodal NK/T-cell lymphoma, nasal-type (ENKTCL) who were mostly treated with anthracycline-based chemotherapy, we propose an easily used nomogram-revised risk index (NRI), validated it and compared with...
Article
Full-text available
Methanol is regarded as an available indicator to analyze the aging condition of cellulose insulation. However, the diffusion mechanism of methanol molecules in the paper-oil insulation system is still unclear, since it cannot be explored by using only experiments. Given this issue, the molecular dynamics simulations were performed to investigate t...
Article
One of the key tasks of the overhead line power equipment inspection based on aerial images acquired by unmanned aerial vehicles is to determine whether the insulators are faulty. However, the fault area on the insulator string occupies a relatively small portion of the entire image, which will make detection difficult. This article presents an int...
Article
Full-text available
Support vector machine (SVM), which serves as one kind of artificial intelligence technique, has been widely employed in transformer fault diagnosis when involving dissolved gas analysis (DGA). However, when using SVM, it is easy to misclassify samples which are located near the decision boundary, resulting in a decrease in the accuracy of fault di...
Article
Full-text available
In recent years, methanol has been proposed as a chemical indicator to assess the aging condition of cellulose insulation in oil-immersed power transformers. However, the formation mechanisms of methanol during cellulose degradation are not clear enough. In this paper, such formation mechanisms were studied using molecular dynamics simulation. Thre...
Article
Full-text available
A novel model for predicting the frequency domain spectroscopy (FDS) curve is reported in this work, which is capable of analyzing the synergistic effect generated by temperature and moisture. The innovation of this work is an exploration of the reported model as a potential tool for predicting the FDS (dispersion loss/permittivity) curves of oil-i...
Article
Full-text available
The distribution behavior of furfural in insulation systems is influenced by the oil–pressboard mass ratio. In addition, the equilibrium distribution of furfural between oil and pressboard will be disturbed after oil replacement. Therefore, it is of great significance to study the distribution ratio of furfural in oil with various oil–pressboard ma...
Article
Expansion of electric grid has induced increasing stress on regional water resources. Yet, few insights have been gained into the network dynamics of virtual water flows embodied in interprovincial electricity transmission. Here, we calculated the interprovincial transfer of virtual water and virtual scarce water associated with electricity transmi...
Cover Page
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mart materials based on nano-dielectrics are actively synthesizing and implementing recently such as submarine cable using XLPE doped with MgO, DC cables using PE with carbon black as an insulation, hydro-generator insulation using nano-silica, motor insulation using hybrid organic-inorganic nano-insulation. The European program Horizon 2020 has de...
Article
Full-text available
Operating temperature is an important parameter of thyristors to ensure the stable operation of power electronic devices. Thermal management technology is of great significance for improving the reliability of thyristors. In this study, the performance of a phase change material (PCM) mesh-finned heat sink is investigated for the thermal management...
Article
Full-text available
The measurement of polarization and depolarization currents (PDC) based on time–domain response is an effective method for state assessment of cellulose insulation material in oil-immersed electrical equipment. However, the versatility of the data obtained at different temperatures is limited because of the temperature dependence of the PDC. In thi...
Article
Full-text available
The quick development of smart grids coupled with IoT devices has opened breaches of security leading to cyberattacks done by attackers with different purposes. In this study, a behavior model is proposed to investigate the risk of cyber attacks on power grids, where the utility value is determined by subjective attack attitude and characteristics...