Insulation Of Electrical Equipment Research Articles

Adsorption and gas sensitivity properties of graphene and Rh-decorated graphene towards SF6 decomposed gases: A DFT study

In order to solve the serious threat of SF6 decomposed gases (H2S, SO2, SOF2, SO2F2) to the stable operation of electrical equipment. In this study, the geometric structure, adsorption energy, density of states (DOS), sensitivity based on band structure and recovery time of H2S, SO2, SOF2, SO2F2 on graphene and Rh-modified graphene (Rh-graphene) were investigated computationally by density functional theory (DFT). The geometric structure of Rh-graphene was optimized with an average Rh-C bond length of 1.891 Å. According to the analysis of DOS and band structure, the electrical conductivity has a little effect of the Rh-graphene compared with pristine graphene, but Rh modification can regulate the band gap of graphene. The adsorption energy (Ead) and the sensitivity (S) at work temperature indicate that graphene has ideal adsorption and sensing properties for SO2 and Rh-graphene reflects the excellent applicability as the SO2 and SO2F2 gases sensor with the sensitivity of approximately −99 % and −60 %, respectively. The Graphene/SO2 system owns the minimum recovery time of 2154.3 ps. The recovery time of Rh-graphene/H2S and SOF2 is several orders of magnitude smaller than Rh-graphene/SO2 and SO2F2. The analysis of DOS and band structure was used to explain the sensing mechanism. The study would lay a theoretical foundation for the development of SF6 decomposed gases sensor for electrical equipment insulation.

Innovative Approach for Detecting Early-Stage Partial Discharges in Instrument Transformers via Ultrasound and Random Forest Analysis

This article introduces a novel technique for detecting and classifying Partial Discharges in Instrument Transformers, addressing the gradual breakdown of external insulation in high-voltage electrical equipment through ultrasound measurements. The use of hand-held probe-microphones for ultrasonic sensing gains prominence for its versatility and online diagnostic capabilities. The proposed method combines insights into partial discharge types and the pollution level within the equipment, thereby transforming ultrasonic readings into useful information and facilitating informed decision-making. Laboratory tests simulate real-world conditions to which current and voltage transformers of 145 kV and 245 kV are subjected. These tests result in ultrasonic and apparent charge measurements, also known as Phase-Resolved Partial Discharges (PRPD). A random forest model achieves over 92 % accuracy in classifying ultrasonic signals into eight class: normal, light partial discharge, light corona, corona, light superficial, light saline pollution, moderate saline pollution and heavy saline pollution; enhancing the understanding and predictive maintenance of instrument transformers.

Partial Discharge Signal Denoising Algorithm Based on Aquila Optimizer–Variational Mode Decomposition and K-Singular Value Decomposition

Partial discharge (PD) is a primary factor leading to the deterioration of insulation in electrical equipment. However, it is hard for traditional methods to precisely extract PD signals in increasingly complex engineering environments. This paper proposes a new PD signal denoising method combining Aquila Optimizer–Variational Mode Decomposition (AO-VMD) and K-Singular Value Decomposition (K-SVD) algorithms. Firstly, the AO algorithm optimizes critical parameters of the VMD algorithm. For the PD signal overwhelmed by noise, the AO-VMD algorithm can decompose it and reconstruct it by using kurtosis. In this process, the majority of the noise is removed, and the characteristics of the original signal are shown. Subsequently, the K-SVD algorithm performs sparse decomposition on the signal after OA-VMD, constructs a learned dictionary, and captures the characteristics of the signal for continuous learning and updating. After the dictionary learning is completed, the best matching atoms from the dictionary are selected to precisely reconstruct the original noiseless signal. Finally, the proposed method is compared with three traditional algorithms, Adaptive Ensemble Empirical Mode Decomposition (AEEMD), SVD-VMD, and the Adaptive Wavelet Multilevel Soft Threshold algorithm, on the simulated signal and the actual engineering signal. The results both demonstrate that the algorithm proposed by this paper has superior noise reduction and signal extraction performance.

Insight into the interface effect and PTC effect on the temperature-adaptive electrical conductivity of epoxy composite

Doping functional fillers into the polymeric matrix is an effective strategy to improve the electrical, thermal, and other performance of insulating materials. It is imperative to understand the influence of fillers on the charge carrier behavior to achieve better regulation effectiveness. In this work, micrometer-sized and nano-sized ceramic particles with positive temperature coefficient (PTC) electrical resistivity are employed to prepare the epoxy composites, whose electrical conductivity under different temperature and electric field, space charge characteristics, permittivity, and electric field distribution are studied. It is found that the doping of a PTC filler shifts the electrical conduction from bulk-controlled to electrode-limited, determining the quantity of charge carriers within epoxy composites. While the interface effect mainly affects the transport process of charge carriers, it would fail to dominate the electrical conduction since the abundant charge carrier introduced by the semiconductive functional filler. Combined with the reinforced interface effect, the electrical conductivity–temperature characteristic of the epoxy nanocomposite is optimized, leading to the reduction in the maximum electric field within electrical equipment insulation by 55%. These findings emphasize the synergistic regulation of charge carrier amount and transport, which contributes to the precision design of polymeric composites doped with functional fillers.

Assessment of the Arc Resistance of 3D-Printed Insulation Materials for Outdoor High-Voltage Applications

High-voltage electrical equipment insulation often uses composite materials like epoxy resin, cross-linked polyethylene, polyurethane, and silicone rubber as encapsulation. 3D printing technology offers a more efficient and cost-effective solution, producing intricate elements without cutting and casting. Research shows that 3D printed materials have comparable properties to polymer-based insulation, but further testing is needed to evaluate their resistance to harsh environmental conditions. This research investigates the arc resistance properties of 3D printed insulation materials for outdoor high-voltage applications, assessing their suitability for outdoor applications. The wet and dry arc resistance tests were performed in accordance with ASTM D495-99 and IEC-60587. The present work investigated three varieties of samples: polylactic acid, epoxy resin, and silicone rubber. The results of the tests reveal that polylactic acid test samples have average wet and dry arc resistance times of 2.5 hours and 1.4 seconds, which is less than silicone rubber and epoxy resin. Additional research is required to comprehend the behavior of arc formation in polylactic acid insulation materials for high-voltage 3D printing applications.

Rapid Recovery Technology of SF6/N2 Mixed Insulation Gas in Electrical Equipment

SF6 mixed gas is widely used as an insulation and arc extinguishing medium in electrical equipment in cold regions of northern China. Due to its low liquefaction temperature, existing gas recovery technologies are unable to achieve efficient and rapid recovery of SF6/N2 mixed insulation gases. In response to this challenge, a two-stage membrane separation and recovery technology has been proposed, which can efficiently and quickly separate SF6 and N2 from the mixed gas. The volume fraction (V/V) of obtained product SF6 gas reaches 90%, and the use of compression and refrigeration units can achieve rapid filling of 50 m3/h mixed gas. At the same time, the enrichment and recovery of trace SF6 gas in the exhaust gas are achieved. After enrichment, the volume fraction (V/V) of SF6 gas reaches 92%, and the volume fraction (V/V) of SF6 gas in the emptied mixed gas is 600 μL/L, far below the national standard value, solving the problems in actual production.

DEVELOPMENT OF A TESTER FOR DIAGNOSTICS OF CABLE LINES STATE WITH XLPE INSULATION

Link for citation: Konev A.A., Khakimyanov M.I. Development of a tester for diagnostics of cable lines state with XLPE insulation. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 9, рр. 216-223. In Rus. Relevance. The moral and physical deterioration of cable lines voltage of 6–10 kV in our country ranges from 40 to 80 %. At the same time, up to 63 % of all accidents in electrical equipment are due to cable line failures. Recently, cables with cross-linked polyethylene insulation have been actively used, for the diagnosis of which special approaches are required. Therefore, the issues of developing high-voltage test facilities for diagnosing the state of insulation of electrical equipment are quite relevant. The authors proposed an original design of a high-voltage test facility that allows generating both direct voltage and alternating voltages of industrial and ultra-low frequencies. A feature of the device is the use of a multifunctional integrated electromagnetic component in it, which combines the functions of both an inductor and a capacitor. The use of this component allows reducing the dimensions and weight of the test facility. The main aims of the research are to develop a design of a high-voltage test facility and to study its characteristics; build a mathematical model and get dependency graphs. Objects: cables with XLPE insulation, high voltage test facilities. Methods: theory of electrical circuits, mathematical modeling, program for mathematical and engineering calculations Mathcad, MATLAB Simulink. Results. The authors proposed the original design of a high-voltage test facility, which makes it possible to generate both direct voltage and alternating voltages of industrial and ultra-low frequencies. The simulation of the installation was carried out. A method for calculating high-voltage test facilities is proposed.

Electrical properties enhancement of natural ester insulating oil by interfacial interaction between KH550-TiO2 and oil molecules

Bio-based sustainable natural ester has a great application prospect in the field of electrical equipment insulation due to its characteristics such as environmental friendliness. In recent years, the use of nanotechnology to improve the electrical and physical and chemical properties of liquid dielectrics has come under the spotlight. Therefore, two bio-based sustainable natural ester insulating oils were prepared in this paper, modified by nano-TiO2 and KH550-TiO2, respectively. The basic physicochemical and electrical properties of two kinds of nano-TiO2 modified insulating oils were tested and compared. And the interfacial interaction between KH550-TiO2 and oil molecules was explored by molecular dynamics. The results showed that the improving effect of KH550 surface modified nano-TiO2 on the electrical properties of insulating oil was superior to that of nano-TiO2, and the optimal concentration was 0.03 g/L. Compared with pure insulating oil, when the concentration of KH550-TiO2 is 0.03 g/L, the breakdown voltage of nano-modified insulating oil was 75.7 kV, increased by 37.9 %, and the dielectric loss factor was 1.03 %, decreased by 59.8 %. DFT calculations show that there are a large number of electron traps at the interface of nano-TiO2. Electron traps can capture free electrons, reduce carrier mobility, and thus improve the breakdown voltage of insulating oil. The band gap width of KH550-TiO2 is 4.15 eV, which is much larger than that of TiO2. The wider the band gap, the harder it is for electrons to transition from the valence band to the conduction band, which explains why the breakdown voltage of KH550-TiO2 modified oil is higher than that of TiO2 modified oil. More importantly, the amino and silicon hydroxyl groups on the surface of KH550-TiO2 carry strong positive electrostatic potential, and can adsorb free electrons and polar molecules in insulating oil. Moreover, the interface adsorption energy between KH550-TiO2 and oil molecular is -806.03 kJ/mol, which greatly improves the dispersion of KH550-TiO2 in natural esters.

Designing a promising sensor for SF6 decomposed gases by using platinum doped-aluminum nitride nanotubes

Developing a sensor for detecting SF6 decomposed gasses is considered important for the insulation of electrical equipment. First-principles density functional theory computations are undertaken to examine the possible use of metal-doped one-dimensional (1D) nanomaterials in gas sensors, and to investigate their sensitivity, adsorption and electronic properties. Within this work, a platinum (Pt)-doped aluminum nitride nanotube (Pt-AlNNT) was used to investigate the adhesion of SF6 decomposed gasses, namely SO2, SOF2, SO2F2. Two possible sites were considered to investigate the stable structure of Pt-AlNNT. The binding energy of the structure with most stability was − 1.314 eV. Also, the sensitivity and adhesion energy of the above-mentioned gasses demonstrated that Pt-AlNNT had more suitable sensing and adhesion properties compared to other materials. The results can provide useful insights into investigating Pt-AlNNT as a suitable sensor for detecting SF6 decomposed gasses for the insulation of electrical equipment.

ERROR ESTIMATION OF THE DEVELOPED METHOD FOR UNGROUNDED AC SYSTEMS TO DETERMINE THE NETWORK INSULATION

The problem of efficient and safe mining has recently become more relevant due to the intensification of production processes, for example, during the operation of electrical installations at mining enterprises, the insulation of electrical networks and electrical equipment undergoes a change in the electrical insulating properties of materials, which reduces the electrical safety. The network insulation admittance determines the safety of electrical receivers and operational personnel in mining facilities, since the current of a single-phase earth fault is directly proportional to the value of the network insulation admittance, and by controlling its active and reactive components, this will allow for a violation of the integrity of the insulation, thereby taking preventive measures. The article depicts the analysis of the reliability of the devised method by estimating the error of insulation parameters in ungrounded AC systems which is done by indirect measurements. Graph-analytical studies of relative root-mean-square error reveal that the accuracy of the calculation in the devised method can be effectually managed by selecting the susceptance of the additional capacitor and accuracy class of measuring units.

High-Frequency Models of Inductive Sensors for Recording Partial Discharges in Electrical-Equipment Insulation

High-Frequency Models of Inductive Sensors for Recording Partial Discharges in Electrical-Equipment Insulation

Theoretical Analysis of External Insulation of Typical Electric Equipment under Impulse Voltage and Research on Design and Verification Method of Margin

Lightning impulse voltage, one of the typical characteristic working conditions for assessing high-voltage power equipment, can be divided into two forms, namely full wave, and chopped wave. The external structure size of the power equipment directly depends on the lightning impulse voltage, but how lightning impulse voltage relates to the external structure size of the power equipment needs to be carefully studied. Firstly, the theoretical analytical expressions of full wave and chopped wave lightning waveforms are given from the perspective of theoretical formulas. And the lightning waveform is considered to be a polynomial superposition of exponential functions. Based on this, the discussion is divided into two typical insulation structure scenarios: 1) the verification and analysis of the space net distance of a 10 m class super long composite insulator; 2) the analysis of the relationship between the breakdown electric field strength of 5 mm tiny oil gap and oil gap spacing. Further, the lightning impulse voltage test was conducted for large hardware structures, and the corona layer mathematical model was obtained through the precise observation of the structure with the ultraviolet imager. The research shows that the lightning impulse voltage mainly checks the external insulation performance of large insulation structures such as bushings and post-insulators. For the internal oil gap duct structure of the large converter transformer, the lightning impulse voltage mainly checks the micro gap insulation strength. Lightning impulse voltage also has a breakdown effect on SF6 insulation gas, but its internal gas decomposition mechanism needs theoretical and experimental analysis urgently. The research content of this paper has certain theoretical and practical guiding value for the optimization design of large insulation structures under lightning impulse voltage.

Back Flashover Probability of the Overhead Power Line Insulation Taking into Account the Soil Ionization and Frequency Response Features

Back flashovers caused by a lightning strike on an overhead power line tower or overhead ground wire give rise to voltage surges dangerous for the insulation of power substation electrical equipment. A pulse back flashover turns into a short-circuit arc leading to the power line tripping. Calculations of voltage surges in a single–circuit 110 kV power line are carried out using the methods of the grounding devices theory, and the back flashover probability is estimated based on the curve of dangerous currents. The insulation back flashover probability for a power line tower with a ground wire in areas with high-resistance soil is determined by the grounding conductor surge impedance. It is shown that the analysis carried out with taking into account the soil ionization and frequency response features yields an essentially lower back flashover probability. The second ground wire placed under the power line wires reduces the inductance of the ground wires, thereby intensifying the spread of current through the grounding conductors of neighboring towers. This leads to a decreased tower voltage and an increased voltage induced on the wires, thus resulting in a decreased voltage across the insulation voltage and, hence, lower back flashover probability. The factors governing a positive effect from using grounding counterpoises of an overhead power line in areas with high-resistance soil are shown, and the conditions under which this effect is achieved are determined.

Residual charge effects on partial discharges' response to varying sub‐kHz voltage frequencies

AbstractPartial discharges (PD) are the ‘cancer’ of electrical insulation. Insulation design and mitigation of PD‐induced degradation should be based on good knowledge of PD phenomena. In that regard, a significant body of knowledge has been built up from concerted research across the world in past decades and on various aspects of PD phenomena under various conditions. However, the work is far from being complete as new challenges arise. One such challenge is that electric power equipment insulation is becoming more exposed to non‐power frequency voltages. Examples are the proliferation of invertor‐based grid‐tied renewable energy sources and other technologies such as high‐frequency power electronic transformers. Questions that are driving continued research in this regard include the reasons for lack of consensus on the findings on how PD characteristics respond to variations in the voltage frequency. This paper presents results of how residual charge influences PD characteristics' response to voltage frequency changes from 1 to 200 Hz. The study approach is implementing the extended 3‐capacitor PD model in MATLAB® Simulink® and validating the findings using the relevant experimental results that are available in literature. The PD type studied is that of an air cavity encapsulated in a polyethylene dielectric. Highlights of the findings are that the extent of the influence of residual charge on PD characteristics depends on the relative magnitude of the residual charge as well as the voltage frequency. The relationships however exhibit non‐monotonous trends. Such results further confirm similar findings and conclusions by other researchers and could be signalling the establishment of a more solid knowledge base for design of insulations that operate at non‐power frequencies.

High-frequency models of inductive sensors for recording of partial discharges in the insulation of electrical equipment

High-frequency models of inductive sensors for recording of partial discharges in the insulation of electrical equipment

Audible acoustic characteristics of epoxy resins with partial discharge

The epoxy resin is the main solid insulating material for electrical equipment. PD (partial discharge) is an important factor leading to epoxy resin aging or failure. Fault detection technology based on audible acoustic imaging has the advantages of real-time monitoring, visibility, and flexibility and is gradually being used in the field of electrical equipment insulation state monitoring. However, the audible voiceprint features of epoxy resins with typical PD defects are not clear, which is not conducive to effective detection and fault diagnosis. Therefore, in this study, the study of audible voiceprint features of epoxy resins with a metal burr, pollution, metal foreign matters, and surface discharge defects was carried out. The discharge audible signals were obtained, and their time and frequency domain features were analyzed. The results show that the discharge audible signals of four PD defects can reflect the occurrence of PD simultaneously with pulse current signals. But the characteristics are obviously different in the time domain, which are embodied in listening perception, persistence, amplitude, and phase. In the frequency domain, the frequency spectra of discharge audible signals of four defects are mainly 5–10 and 13–24 kHz. Furthermore, the three feature vectors of frequency spectrum complexity, high-frequency energy factor, and maximum frequency point are extracted, which can well distinguish the discharge audible signals of four PD defects.

Rhn (n = 1, 2) modified C3N: A potential candidate for H2S, SOF2, SO2F2 and SO2 detection and scavenging

Since high voltage insulation equipment fault and aging are always accompanied with insulation gas decomposition, it is critical to monitor and scavenge SF6 decomposition gases. In this paper, based on density functional theory, Rh and Rh2 doped C3N are utilized to detect SF6 decomposition species (H2S, SO2, SOF2, and SO2F2). The ideal binding energy of the most stable structures are −2.769 eV (Rh-C3N) and −3.482 eV (Rh2-C3N), respectively. The Rhn-C3N composite structure considerably increases the adsorption behaviors and electrical properties of SF6 decomposition species. After gas molecules adsorption, changes of differential charge density, density of state, work function, and theoretical recovery time further support the sensing characteristic of composite structures. For various target gases, the results reveal that Rh-C3N and Rh2-C3N exhibit distinct adsorption types. SO2 and H2S adsorption belongs to physical adsorption, while the type of SOF2 and SO2F2 adsorbed system is chemical adsorption. Even at high temperatures, the good recovery time (30.32 s and 21.77 s) for H2S adsorption systems can be acquired. The results demonstrate that Rhn-C3N (n = 1,2) is a novel carbon-based SF6 gas sensing material that can be used to diagnose SF6 decomposition in SF6 electrical equipment insulation faults.

THE USE OF PERSONAL PROTECTIVE EQUIPMENT WHEN APPLYING A POLYMER COATING TO EXTERNAL INSULATION IN EXISTING ELECTRICAL INSTALLATIONS

The application of hydrophobic coatings based on organosilicon polymers is one of the effective methods of ensuring the required level of reliability of electrical equipment insulation operation on the surface of which a layer with high electrical conductivity can form. An important aspect of such works is protection of life and health of workers from harmful and dangerous factors by means of personal protective equipment. It is noted that the formation of requirements for their use, as well as the rules of selection and provision is carried out according to the assessment of risks for the health of workers. Improvement of the labor protection system at Ukrainian enterprises is based on the Order of the Ministry of Social Policy of 29.11.2018, which actively cooperates with the International Labor Organization. The purpose of the study is to determine the most likely risks when performing work on polymer coating at the existing power facilities, the analysis of existing personal protective equipment against these risks assessment of the convenience of their application. For this purpose the data from the Registers of risks of the enterprises where the works were performed, own observations, impressions and recommendations of the team members were used. The overwhelming majority of equipment which was covered with the coating falls on the voltage classes of 110 kV and above. The size and location of such equipment require the mandatory use of safety harnesses and safety helmets. The technological procedure of coating deposition was considered and the factors which can cause damage to the health of the employees were singled out. The principles of operation of different types of personal protective equipment against these factors and peculiarities of their application when working at the operating power facilities are analyzed. Particular attention is paid to respiratory protection equipment. Signs are marked, at appearance of which it is necessary to perform operative replacement of protective means. The conclusions from the study defined the minimum equipment of personal protective equipment which must be provided to the employees of the teams for applying hydrophobic polymer coating.

Power Leakage Monitoring and Warning Device for Power Grid Fault Diagnosis: Design and Field Test

Electrical equipment insulation damage, metal shell conduction on rainy days, and wire short circuits are easy to produce leakage, which form step voltage on the ground and endangers the life and safety of nearby personnel. In addition to the existing leakage protector, a new method is proposed to use leakage energy to obtain energy and early warning. The step voltage generated by the leakage current is collected through the electrode, which is rectified and reduced by the nano power LTC3588, while energy is stored in the supercapacitor for the superheterodyne transmitting module to send the leakage signal to the nearby receiving device. Based on the possibility of the superheterodyne transmitting module sending the leakage signal, it is judged whether leakage occurs here. The experimental results illustrate that when 10 mA leakage occurs in a 220 V wire, the electrode distance is 1.0 m, while the energy extraction device can obtain 360 MW of power for the superheterodyne transmitting module to send the leakage signal.

Molecular-dynamics study on the thermodynamic properties of nano-SiO2 particle-doped silicone rubber composites

Polymer dielectric materials doped with nanoparticles show promising applications in the insulation of electrical equipment. In experiment, however, the doping amounts of nanoparticles significantly affect the mechanical and dielectric properties of polymer nanodielectrics. In this paper, the doping amounts and agglomeration of nanoparticles are considered in molecular dynamics (MD) simulations to reveal the probable microscopic mechanism. The effects of doping amounts and agglomeration of nano-SiO2 particles on the thermodynamic properties of silicone rubber (SR) nanocomposites are studied from the aspects of the mean square displacement, free volume fraction, pore size distributions, interaction energy, cohesive energy density and hydrogen bond analysis. The results show that with increasing doping amounts of nano-SiO2, the interfacial interactions and intermolecular force of the SR composites are enhanced. Therefore, the mean square displacement, the free volume fraction and the maximum pore size for SR composites all decrease, which is beneficial to the improvement of mechanical and dielectric performances for nano-SiO2/SR composites. However, the agglomeration of nano-SiO2 particles (the increase of the size of nanoparticles), will lead to a decline in the intermolecular forces among SR chains and the destruction of hydrogen bond networks. Therefore, the mean square displacement, the free volume fraction and the maximum pore size in SR composites will increase, which will degrade the mechanical and dielectric performances of SR composites. This work reveals a generalized relationship between the doping amounts and agglomeration of nanoparticles and the thermodynamic properties of polymer dielectric composites.