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Abstract The valve‐side bushing of the UHV converter transformer is the key equipment in the DC transmission project, and its running state directly affects the security and stability of the power system. This paper analyses the attributes of the physical entities, uses the digital twins to establish the state feature set and proposes a zero‐sample state evaluation algorithm for the valve‐side bushing. First, the geometric, materials and electrical characteristics are analyzed, and the detailed components of carrier current are obtained by empirical mode decomposition. Then, COMSOL is used to establish digital twins, verify the validity of twins with axial heat distribution of bushing, and establish a state feature set with the extreme temperature inside and outside bushing. Finally, the fuzzy clustering algorithm is used to classify the state feature set, and the similarity is used as the index to realize the zero‐sample state evaluation of the valve‐side bushing. Through the demonstration and analysis of examples, the evaluation model solves the problems of difficulty in extracting the internal features, fewer fault samples, and training difficulty, which is conducive to improving the operation and maintenance management level of power transmission equipment.

Abstract Herein, the surface charge characteristics of a tri‐post insulator in a ± 500 kV direct current gas‐insulated transmission lines (DC‐GIL) filled with SF6 are thoroughly studied. The influences of volume and surface conductivity of the insulator on the surface charge and consequent electric field distribution are discussed. An improved method is introduced to obtain the distribution of surface charge with considerable accuracy and efficiency for the calculation. It is found that with increasing the volume conductivity, the dominative conduction mechanism changes from surface conduction to bulk conduction, while the inverse variation appears with increasing the surface conductivity. During the variation of electric conductivity, obvious effect of surface charge accumulation is found on the electric field distribution involving the variation of peak electric field strength and its location. Besides, high charge density usually appears along with low peak field strength during this variation. It can be concluded that the surface charge accumulation should be paid special attention when analysing the insulation characteristics of tri‐post insulators. The variation of volume and surface electric conductivity should be thoroughly considered.

The temperature distribution of the tri‐post insulator in a ±500 kV direct current gas‐insulated transmission lines (DC‐GIL) is investigated. The influence of thermal gradient on the electric field characteristics is investigated as well. A horizontally installed GIL model is applied in the simulation. The thermal and electric parameters of the insulator are measured and employed. The temperature results indicate that the gas shows a layered distribution pattern while the insulator shows a radial distribution pattern. The temperature of the upper post is higher. With increasing ambient temperature, the surface temperature increases linearly following the variation of ambient temperature. With increasing load current, the temperature near the conductor shows an obvious increase. With increasing gas pressure, the temperature decreases due to the promotion of convection. Besides, the electric field strength of the insulator surface increases if the surface temperature increases during the variation of operating conditions. And the peak of field strength moves towards the enclosure. After 10 h, the temperature reaches a quasi‐stationary state. Since the thermal gradient affects the distribution of gas density and electric field strength of the insulator, the investigation of temperature characteristics is necessary when evaluating the insulating performance of DC‐GIL with insulators. [ABSTRACT FROM AUTHOR]

The valve‐side bushing of the UHV converter transformer is the key equipment in the DC transmission project, and its running state directly affects the security and stability of the power system. This paper analyses the attributes of the physical entities, uses the digital twins to establish the state feature set and proposes a zero‐sample state evaluation algorithm for the valve‐side bushing. First, the geometric, materials and electrical characteristics are analyzed, and the detailed components of carrier current are obtained by empirical mode decomposition. Then, COMSOL is used to establish digital twins, verify the validity of twins with axial heat distribution of bushing, and establish a state feature set with the extreme temperature inside and outside bushing. Finally, the fuzzy clustering algorithm is used to classify the state feature set, and the similarity is used as the index to realize the zero‐sample state evaluation of the valve‐side bushing. Through the demonstration and analysis of examples, the evaluation model solves the problems of difficulty in extracting the internal features, fewer fault samples, and training difficulty, which is conducive to improving the operation and maintenance management level of power transmission equipment. [ABSTRACT FROM AUTHOR]

Herein, the surface charge characteristics of a tri‐post insulator in a ± 500 kV direct current gas‐insulated transmission lines (DC‐GIL) filled with SF6 are thoroughly studied. The influences of volume and surface conductivity of the insulator on the surface charge and consequent electric field distribution are discussed. An improved method is introduced to obtain the distribution of surface charge with considerable accuracy and efficiency for the calculation. It is found that with increasing the volume conductivity, the dominative conduction mechanism changes from surface conduction to bulk conduction, while the inverse variation appears with increasing the surface conductivity. During the variation of electric conductivity, obvious effect of surface charge accumulation is found on the electric field distribution involving the variation of peak electric field strength and its location. Besides, high charge density usually appears along with low peak field strength during this variation. It can be concluded that the surface charge accumulation should be paid special attention when analysing the insulation characteristics of tri‐post insulators. The variation of volume and surface electric conductivity should be thoroughly considered. [ABSTRACT FROM AUTHOR]

The development of electricity users induces significant design needs in the field of electrical installations. These needs naturally arise from increased requirements, with regard to the quantity and quality of service provided by these facilities. Therefore, the consumption of electrical energy is increasing day by day, and the assurance of its supply has become an unavoidable imperative. The continuity of this offer requires a suitable design and sizing of the HV/A transformer stations, which constitute the essential part in the field of the distribution of electrical energy. Through this report, we tried to make a study on the substations of distribution HV whereas our objective was to gather the most possible information in order to work out a document, which makes it possible to give the maximum of details on the coordination of insulation in HV/A substation equipment. [ABSTRACT FROM AUTHOR]

The paper presents the development of a megavolt-class SF6-insulated radial switch. The switch is used as a crowbar in a MV Tesla-type generator to produce pulsed electric fields in very large volumes, for proof-of-concept experimentation of a novel non-invasive food processing technology. The main features of the switch include: (1) Using SF6 gas as the insulation gas; (2) a breakdown channel along the radial direction, rather than axial; (3) a compact configuration with its volume limited to 3.2 L. In order to achieve a ruggedized high voltage insulation as well as an enhanced operation safety, the following design techniques were applied: (1) Structures of the switch were well designed to minimize the local electric filed in the cathode triple junctions; (2) the grooves of surface of the insulators that enclose the switch were finely optimized to keep the surface flashover under control; (3) a prolate spheroid geometry of the high voltage electrode was adopted to achieve a better control of the gas breakdown. This paper describes in detail the design and the preliminary test of this switch. [ABSTRACT FROM AUTHOR]

The paper presents the development of a megavolt-class SF6-insulated radial switch. The switch is used as a crowbar in a MV Tesla-type generator to produce pulsed electric fields in very large volumes, for proof-of-concept experimentation of a novel non-invasive food processing technology. The main features of the switch include: (1) Using SF6 gas as the insulation gas; (2) a breakdown channel along the radial direction, rather than axial; (3) a compact configuration with its volume limited to 3.2 L. In order to achieve a ruggedized high voltage insulation as well as an enhanced operation safety, the following design techniques were applied: (1) Structures of the switch were well designed to minimize the local electric filed in the cathode triple junctions; (2) the grooves of surface of the insulators that enclose the switch were finely optimized to keep the surface flashover under control; (3) a prolate spheroid geometry of the high voltage electrode was adopted to achieve a better control of the gas breakdown. This paper describes in detail the design and the preliminary test of this switch.

In order to study the influence mechanism of dielectrically coated electrode in SF6 gas under DC electric field on metal particle lift-off, experimental platform is setup and motion trajectory is recorded by high-speed camera. The experiment shows that with the increasing of SF6 gas pressures, the lift-off field of metal particle is increased and the time to reach the high-voltage electrode shortened. Instantaneous displacement of metal particle is gained by image processing and computational method of charge quantity is raised, analysing of charge quantity shows that the metal particle's charge quantity decreases. Meanwhile, theoretical analysis model of field distribution around metal particle is established, result indicates that there is an enhance of electric field between coating and metal particle and a transform of charge density distribution, which leads to a downward polarisation force for metal particle. The decreasing of the electric charge quantity and the downward polarisation force results in the increasing of the lift-off field. This article maintains that partial discharge is the charging mechanism of metal particle; the enlargement of SF6 gas pressure brings about the raise of initial electric field of partial discharge, causing the increase of downward polarisation force with higher electric field to lift-off. [ABSTRACT FROM AUTHOR]

In this paper, the gas flow model of high voltage SF6 circuit breaker arc quenching chamber was established to analyse the nozzle high speed gas flow variation characteristics using finite volume method, and k-ɛ turbulent equation combined with the wall function was analysed. According to the similarity theory, the similarity criteria and the equivalent model for the arc quenching chamber was established and simulated for reflecting the aerodynamic behavior under cold gas flow interruption condition. [ABSTRACT FROM AUTHOR]

Statistical characteristics of discharge magnitude are significant for insulation diagnosis by monitoring partial discharge (PD) in power apparatuses. However, hitherto, investigations on the PD magnitude distribution in SF6 gas under direct current voltage are insufficient. A current pulse measuring circuit and a ultra‐high‐frequency (UHF) antenna were simultaneously employed to investigate characteristics of positive corona in 0.3 MPa SF6 gas. It is found that compared to the UHF antenna, the common measurement impedance used in laboratories caused several current pulses overlapped, resulting in pulse burst phenomenon. The pulse burst was easily mistaken as a single PD, which actually contained several PDs, thereby negatively affecting obtaining a real discharge magnitude distribution. Moreover, the discharge magnitude distributions were compared when a pulse burst was treated as a single PD and several PDs, respectively. It is found the former and latter one had forms of non‐skewed two‐parameter Weibull distribution with large‐scale parameters and positively skewed two‐parameter Weibull distribution with small‐scale parameters, respectively. Based on this understanding, the change of the distributions with time was investigated, and the results showed that the distribution would have a permanent form of two‐parameter Weibull distribution after a 24‐h transition time. [ABSTRACT FROM AUTHOR]

The decomposition component analysis method can be used to monitor and diagnose the insulation state of SF6 electrical equipment in power industry. Here, the authors firstly compared the advantages and disadvantages of various SF6 decomposition products detection methods and analysed their feasibility of online monitoring. Then the requirements of SF6 decomposition products online detecting technology according to the actual engineering needs were discussed. The SF6 decomposition products online detection system has been mainly introduced from the aspects of principle, structure, detection effect, and practicability. The research points and development tendency of SF6 decomposition products online detection system is forecasted. [ABSTRACT FROM AUTHOR]

Surface charge accumulation on spacer is an important factor to cause surface flashover. An experimental set‐up is established to measure surface potential over a truncated cone‐type spacer under DC voltage in SF6 gas at atmospheric pressure using a Kelvin vibrating electrostatic probe. The surface charge density is calibrated based on multipoint measurement technique, which takes the influence of electrostatic probe into account. The experimental results show that surface charge distribution patterns can be divided into three classes including centrosymmetric distribution, spot‐like distribution, and cloud‐like distribution. The symmetrically distributed charges are injected by electrode, which migrate along spacer surface through the surface conductivity. While the charges showing spot‐like and cloud‐like distribution are generated by the ionisation of SF6 due to local electrical field concentrated. Besides, the hetero‐charges are more easily to be saturated with different charging durations and the polarity of the net charge is the same as that of applied voltage. [ABSTRACT FROM AUTHOR]

SO2 is a symbolic gas that can indicate the insulation status of SF6 insulation electrical equipment. Its accurate quantitative measurement is of the great significance for the judgement of the type and severity of faults inside the insulation equipment. For this reason, a detection system of trace SO2 based on ultraviolet (UV) spectrometry was presented. The measured UV absorption spectra of SO2 were processed using the wavelet analysis to remove useless spectra information and get the UV differential absorption spectra of SO2. The fast Fourier transform (FFT) was used to analyse UV differential spectra in the band of 190–230 and 290–310 nm and extract the feature information. The results show that there is a good linear relationship between the FFT characteristic peak value and the concentration of trace SO2 in the two wave bands. The detection limit in the band of 190–230 nm was even lower than that in the band of 290–310 nm. Besides, the differential absorption cross section of SO2 decreases with the increase of temperature. The study has laid a foundation for the application of the UV differential absorption spectroscopy in the online monitoring and fault diagnosis of SF6 insulation electrical equipment. [ABSTRACT FROM AUTHOR]

SO2 is a symbolic gas that can indicate the insulation status of SF6 insulation electrical equipment. Its accurate quantitative measurement is of the great significance for the judgement of the type and severity of faults inside the insulation equipment. For this reason, a detection system of trace SO2 based on ultraviolet (UV) spectrometry was presented. The measured UV absorption spectra of SO2 were processed using the wavelet analysis to remove useless spectra information and get the UV differential absorption spectra of SO2. The fast Fourier transform (FFT) was used to analyse UV differential spectra in the band of 190–230 and 290–310 nm and extract the feature information. The results show that there is a good linear relationship between the FFT characteristic peak value and the concentration of trace SO2 in the two wave bands. The detection limit in the band of 190–230 nm was even lower than that in the band of 290–310 nm. Besides, the differential absorption cross section of SO2 decreases with the increase of temperature. The study has laid a foundation for the application of the UV differential absorption spectroscopy in the online monitoring and fault diagnosis of SF6 insulation electrical equipment. [ABSTRACT FROM AUTHOR]

Aimed to clarify the correlation characteristics between the internal partial discharge (PD) in the negative direct current (DC) gas‐insulated system (GIS) and gas pressure, and to establish an insulation fault diagnosis method based on decomposition component analysis, this study on PD decomposition of sulphur hexafluoride (SF6) was conducted under different pressures on the basis of constructing a SF6 decomposition experimental platform under DC PD. A stainless steel needle‐plate electrode was used to simulate the insulation defects of metal protrusions in GIS. SOF2, SO2 F2, CO2, SO2, and CF4 data generated from SF6 decomposition were obtained under different pressures. The variation law of component concentration and effective characteristic ratio with pressure were analysed in detail. In addition, a mathematical formula for pressure and decomposition components was deduced according to gas micro‐ionisation theory. The effective content and formation rate were defined to validate the relationship. Results show that the concentration of SF6 decomposition components decreased gradually with increasing pressure with a strong regularity. Furthermore, the relationship between pressure and component concentration derived from the theory can explain the relationship between the effective content of SF6 decomposition components and the effective formation rate and pressure variations. [ABSTRACT FROM AUTHOR]

Voltage–time (V –t) characteristics of the SF6 long gap under very fast transient overvoltage (VFTO) draw wide attention at the high‐voltage transmission systems. In this research, a generating system of VFTO and lightning impulse (LI) up to 2.5 MV was set up. The V –t characteristics for SF6 gaps with hundreds of millimetres length under negative LI and VFTO were researched. Experimental results indicated the rate of rising of V –t curve for the sphere‐plane gap under VFTO was moderate, and V –t curve under LI was rapid, resulting in the intersection of the two types of V –t curves. However, for the rod‐plane gap, the V –t curve under VFTO was below that under LI at 0.5 MPa. The shape of V –t curve had many relationships with discharge propagation velocity in the SF6 gap, which was determined by the gap distance, field non‐uniformity, gas pressure and applied voltages. Based on analysis of discharge process and physical background of V –t curve, the semi‐empirical formulae were derived and the prediction model was established. It was demonstrated the predicted V –t curves could accurately predict breakdown characteristics of long SF6 gas gaps [ABSTRACT FROM AUTHOR]

Dynamic resistance measurement (DRM) was proved to be an important method for condition assessment of contact sets of SF6 circuit breakers (CBs). The erosion of contact sets due to arc energy is a main factor that influences the electrical lifetime of the extinguishing chamber. In this study, a high‐voltage CB synthetic circuit was used to produce fault current for electrical erosion tests on the contact sets. The contact sets were close to the end of their service life after a series of erosion tests. DRMs with DC amperages of 0.5, 1.0, and 1.5 kA were conducted on the two tested breakers in the interval of each erosion test. Five essential diagnostic parameters were extracted from the contact resistance curves as a function of contact travel. The variation of these parameters during the whole erosion tests were investigated to find an effective condition assessment method for contact sets. From the power balance at the contact surface, the material erosion rate due to metal evaporation for each erosion test was calculated and in good agreement to the experimental results. Finally, the contact length and contact resistance were employed as diagnostic parameters for condition assessment of contact sets. [ABSTRACT FROM AUTHOR]

This study examines how byproducts from thermal decomposition of sulfur fluoride (SF6) can be measured and applied to diagnose an overheating fault occurring in SF6 insulated equipment. Using a series of experiments performed on a SF6 thermal fault simulation system, the thermal decomposition characteristics of SF6 were obtained for temperatures below 400°C. Based on these results, the formation rate was extracted to indicate the progress of the thermal fault's development, and the characteristic component ratio was used to identify the type and severity of the thermal fault. The relationship of the fault temperature and the formation rate along with the correlation between the characteristic ratio and the fault temperature were studied. The results show that: the formation rate of the components effectively reflects the severity and development trend of the thermal fault; by integrating the IEC standard 60480‐2004, the obtained thermal fault maximum safe time (TMS) can accurately indicate the largest safe time when thermal fault happens; component characteristic ratios C(SO2)/C(SO2F2) and C(SO2F2+SOF4)/C(SOF2) can be used to evaluate whether the fault type is a thermal fault; and the thermal correlation ratio (TR) can be employed to recognize the temperature value from 300°C to 400°C. [ABSTRACT FROM AUTHOR]

To obtain the inner correlation feature between SF6 decomposition characteristics caused by the partial discharge (PD) of the free metal particle insulation fault and charge magnitude, a series of experiments are conducted on the designed experimental system. Three methods, namely, gas chromatograph, chromatography‐mass spectrometry and Fourier infrared spectroscopy, are used to quantitatively measure the decomposed components. Their content relation under different PD magnitudes is obtained and determined as SOF2 > SiF4 > SOF4 > SO2F2 > SO2 > S2F10 > CO2 > CF4, where the content of highly toxic S2F10 greatly exceeds its safe threshold. The study also discusses the correlation feature between each component of the free metal particle insulation fault and charge magnitude, which is found only when the charge magnitude reaches the point where it promotes the obvious formation of the components. Each component formation is found positively related to PD quantity. Based on a stability analysis of the produced components, five components are proposed to represent PD strength and the diagnosis table to recognise the severity of the metal particle insulation fault. This study attempts to lay a solid foundation for the conditional assessment of SF6 insulated equipment. [ABSTRACT FROM AUTHOR]

The detection of gas decomposition products is widely used to diagnose the inner condition of SF6-insulated electrical equipment for its anti-interference ability and high sensitivity. A discharge chamber with Teflon coating inside was designed, with adjustable defect parameters and the volume nearly the same as real ones in gas-insulated switchgear. With the assistance of newly developed dual gas chromatography detection system, this paper investigated the influences of relatively low moisture on the discharge characteristics and gas decomposition under corona and mild spark in SF6. Considering notable hydrolysis reactions in the main gas volume and on the vessel walls, SO2F2, SO2, and S2OF10 were selected as typical gas decomposition products. The average discharge capacity and its fluctuation were found to decrease with the increase of moisture content within research scope, which is related to the electronegativity of water molecule. The concentration of typical decomposition products under various moisture conditions was observed in detail. The results show that in mild spark, O atom in S2OF10 mainly originated from oxygen rather than water vapor in SF6. To diagnose internal insulation condition by only monitoring, the magnitude of discharge capacity is proved unreliable. A new parameter, the concentration ratio of SO2/S2OF10, was proposed to group moisture content and discharge types. [ABSTRACT FROM PUBLISHER]

This article introduces a comprehensive survey on new trends in high-voltage (HV) power circuit breakers (CBs) technology. Applying the new puffer and the self-blast technologies, the ratings of SF6 CBs have reached upto 1,100 kV, 80 kA, and 50 GVA, which is the world's largest gas insulated switchgear (GIS), with independent pole operation and utilizing the advantages of external composite insulators. Several new vacuum arc control technologies are discussed. New generations of controlled intelligent switching devices that implement new power electronic actuating devices are introduced. Finally, superconducting fault current limiters (SFCLs) are introduced. SFCLs have two main properties: current limitation capability and ultra high-speed operation. SFCLS could be a key technology for future power systems engineering [ABSTRACT FROM PUBLISHER]

A preliminary description of a new arc representation has been introduced in . In which, the Modified Mayr (P-τ model) arc equations are solved in the transient analysis control system (TACS) field of the electromagnetic transient program (EMTP) and represented in the power network by TACS controlled voltage source. In this paper, substantial improvements of this representation are carried out. A performance comparison with the EMTP built-in Avdonin model is incorporated to validate the proposed representation effectiveness. SF6 breakers with experimentally defined arc parameters are used to perform this comparison. The thermal limiting curve is computed by the proposed and the built-in models and compared with the measured characteristic. Also, universality of representation is verified via carrying out different arc model examples of circuit breaker and transmission-line arcing faults. The study results validated the proposed representation regarding accuracy and universality. [ABSTRACT FROM PUBLISHER]

A comparative analysis of the parameters of reliability of switchgears with SF6 and conventional insulation is performed. It is shown that the use of gas-insulated switchgears is preferable for the conditions of the power system of Russia. Ways of renovating switchgear equipment in the networks of power systems are outlined. [ABSTRACT FROM AUTHOR]

Conducting particles in transmission and switching equipment insulated by compressed sulphur hexafluoride (SF6) can result in loss of as much as 90% of the gas dielectric strength. Particles in practical systems can exist in a wide variety of shapes and sizes, and of materials of different densities. In this paper, the effect of particle size on the probability of SF6 breakdown is discussed. Theoretical and experimental results are presented. [ABSTRACT FROM PUBLISHER]

This letter presents a side-hole fiber-based extrinsic Fabry-Perot interferometric (EFPI) sensor whose cavity was filled with sulfur hexafluoride (SF6) for in situ power transformer partial discharge detection. The Fabry-Perot cavity was formed by a polished thin diaphragm and a cleaved side-hole fiber that were thermally fused onto a fused silica ferrule. The cavity was first vacuumed and then inflated with 300-kPa SF6 through the fiber side holes to increase its resistance to electric stress. Experimental results show that the sensor filled with SF6 was able to withstand electric stress of at least 10 kV/mm (ac root-mean-square value) in transformer oil, three times larger than that of a traditional air-filled EFPI sensor. [ABSTRACT FROM PUBLISHER]

In this letter the dynamics of wire particles in a coaxial gas insulated transmission line (GITL) system with coated electrodes under AC voltage are studied using a computational algorithm. The possibility of the SF6 gas insulation breakdown due to the presence of metallic contaminants was computed at different applied voltages and gas pressures [ABSTRACT FROM PUBLISHER]

Gas-insulated transmission lines (GIL) are a further development of the tubular conductor intended for long distances and are especially suitable for connecting conurbations to centers of power supply. They are also as “invisible” as ordinary power cables as well as having a number of other advantages. The first mixed-gas-insulated power transmission line in the world successfully completed its field trials with an endurance test in early 1999. The most important aim in the further development of tubular conductors for long-distance power transmission was to reduce costs so that they can be used economically over distances of up to several kilometers. This has now been achieved. The system costs of the gas-insulated transmission lines developed by Siemens are now only a factor of 8 or 10 above those of overhead power lines, down from a factor of 30. Now the GIL has reached the order of magnitude to be accepted by utilities if an overhead line must be brought underground. The basis of this reduction in costs was: adaptation of installation techniques similar to those used in laying pipelines; simplification and standardization of individual components; and use of a sulfur hexafluoride (SF6) and nitrogen (N2 ) gas mixture. In the past, pure SF6 has been the most widely used gas for tubular conductors, most of which have been incorporated into substations [ABSTRACT FROM PUBLISHER]