Gas-insulated Metal-enclosed Switchgear Research Articles

Stress Measurements of GIS Epoxy Composite with Transverse Waves Based on the Ultrasonic Pulse-Echo Method

The mechanical reliability of the gas-insulated metal-enclosed switchgear (GIS) is critical to the safe and stable operation of a power system. The internal stress induced in GIS insulators, which typically lead to cracking, can degrade the mechanical properties and compromise the reliability of the GIS. In this work, ultrasonic nondestructive measurements of the internal stress in a GIS 126 kV epoxy composite with the transverse waves are demonstrated for the first time. Our results show that the velocities of ultrasonic transverse waves increase linearly with the compressive stress and decrease linearly with the tensile stress. The acoustoelastic coefficients are −1.18 × 10−4/MPa and −1.96 × 10−4/MPa for measurements with transverse waves polarized vertically and parallelly to stress, respectively. Based on these acoustoelastic coefficients, the internal stresses are calculated, and the maximum absolute values of relative errors are 35.4% and 26.3% for measurements with the transverse wave polarized vertically and parallelly to stress, respectively.

Finite element analysis of reinforcement for gas insulated switchgear

Considering the burgeoning requirement for reinforcing gas-insulated metal-enclosed switchgear, a three-dimensional elastic-plastic finite element model was established to examine the stress distribution before and after reinforcement. The results showed that, under an internal pressure of 3.8 MPa, the maximum stress of the defective sample surpassed the yield strength of the material, leading to its destruction. On the other hand, the maximum stress value of the reinforced sample, with a gel and a reinforcing plate, decreased to 145 MPa and was lower than the yield strength of the material. Moreover, the results of the hydrostatic test further demonstrated that the gel was effective in reducing the stress concentration at the defect within a certain range. In particular, the results indicated that the gel was capable of decreasing the maximum stress value by 33 MPa, thereby safeguarding the structural integrity of the switchgear.

Applicability of the acoustic–electrical joint detection method to identify defects in gas insulated system

AbstractThere are many defects in gas‐insulated metal‐enclosed switchgear (GIS) and gas‐insulated transmission lines (GIL) that may cause accidents, such as floating potentials, metal particles, air gaps, and cracks in support insulators. Nevertheless, to‐this‐date, there is no effective method to recognize them to adjust their operation status. Accordingly, this study compared three typical defect models to explore the partial discharge process, and three typical experimental models were established to identify the characteristic parameters of acoustic and electrical information in the development of defects. The research study shows that that as the voltage increases, the partial discharge of free‐metal‐particle defects and air‐gap defects obtained by the pulse‐current method increase gradually. A sudden increase also occurred in the partial discharge of the floating potential defect. The discharge amount of free conductive particles obtained by an ultrahigh‐frequency detection method was distributed symmetrically on both sides of the applied voltage peak, and the other two defects were on one side of the peak and yielded an obvious phase difference. The particle collision signal obtained by the ultrasonic method was obvious, but had no obvious phase relationship with the applied voltage. However, the obtained floating potential defect information had obvious phase differences, and the ultrasonic method was not sensitive to air‐gap defects. The three typical defects can be identified by the combined method more accurately; this provides a theoretical basis and data support for GIS and GIS voltage tests, detection technologies, and online monitoring methods.

Analysis and detection of fault for substation GIS insulating part based on integrated automation system data

Insulators are important components in gas-insulated metal-enclosed switchgear (GIS), and their safe operation is of great engineering significance. In an air leakage fault accident caused by the cracking of the insulating part of the grounding knife switch of 500kV HGIS equipment, the following measures were taken to find out the cause of the failure: disassembly inspection, equipment assembly review, insulation performance test and residual stress analysis during casting and curing. It turned out that the failure was caused by a lack of cache firmware in the production process. The thermal conductivity and thermal expansion coefficient of the central copper conductor and epoxy resin are different. When the two are solidly adhered, the incompletely reacted insulating parts shrink too quickly when the temperature difference is too large. The copper conductor locally produces excessive residual stress to the epoxy resin, which causes the insulation to crack. According to the causes of the fault, suggestions are put forward, such as replacing the central copper conductor with aluminum material, adding secondary pre-curing procedure in the production process, and adding Remote longitudinal Wave probe on the Insulated Basin side to monitor residual stress in real time.

Exploration on Automatic Management of GIS Using TL-CNN and IoT

The research aims to effectively monitor the state of complex industrial equipment in real time, diagnose the internal Partial Discharge (PD) pattern of Gas Insulated Metal Enclosed Switchgear (GIS), implement effective health management, and change the traditional model optimization route of increasing training time in exchange for performance improvement. This paper studies the complex equipment-oriented Health Management System (HMS) based on Internet of Things (IoT) technology and Transfer Learning. Firstly, the principles of Transfer Learning and Deep Learning (DL) technology are introduced. Secondly, the requirements of GIS internal status recognition and management are studied. Furthermore, a GIS-oriented HMS based on Transfer Learning-optimized Convolutional Neural Networks (CNN) is proposed, and the training dataset is constructed. Finally, the proposed model is tested. The results show that the complex equipment-oriented HMS based on IoT technology, CNN, and Transfer Learning can detect the internal status of GIS in real time. Compared with the traditional DL algorithm and expert system, the proposed model has a shorter training time of only 16min, faster convergence speed, high testing recognition rate, and over 96% recognition rate. Compared with other mainstream algorithms, it has higher identification, the storage parameter volume is 408, and the storage space is 12.8MB. Moreover, the proposed Transfer Learning-optimized CNN model can accurately detect the status of GIS, identify abnormal statuses, and help prolong the service life of GIS. The proposed complex equipment-oriented HMS contributes to the intelligent manufacturing industry and provides a new direction for applying emerging Computer Technology in the intelligent industry.

Research on Fault Vibration Signal Features of GIS Disconnector Based on EEMD and Kurtosis Criterion

Gas insulated metal enclosed switchgear (GIS) has been widely used in the world because of its compact structure and adaption to the environment. However, due to frequent operation and other reasons, GIS disconnector is prone to mechanical failure with poor contact, leading to abnormal vibration signals. In this paper, a GIS disconnector contact fault simulation platform is built to collect vibration signals in three states: normal contact, moderate poor contact and severe poor contact of disconnector contact. The Ensemble Empirical Mode Decomposition (EEMD) method is used to decompose the vibration signals, and the IMF decomposition signals are screened by Kurtosis criterion (a numerical statistic method). Finally, the vibration signal features of GIS under different conditions are obtained by reconstructing the screening signals. The results indicate that, under the normal contact, the frequency of GIS vibration signal mainly presents the distribution of 100 Hz and its integer multiple frequency component, when there is a contact defect, the high frequency component in the vibration signal spectrum increases significantly, and the tripling frequency component is present, and the amplitude of component will increase with the severity of the fault. Therefore, this study provides a theoretical reference for on‐line monitoring of GIS disconnecting switch contact fault. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

An Ultrasonic Nondestructive Testing Method for Density Uniformity of Basin-Type Insulators in GIS

A large density difference of a basin-type insulator in gas-insulated metal-enclosed switchgear (GIS) weakens its mechanical strength, which will threaten the safe and stable operation of GIS. In this article, an ultrasonic nondestructive testing method for density uniformity of GIS basin-type insulators was proposed. First, seven standard samples with different Al2O3 content were tested by an ultrasonic testing system, and then a mapping relationship between density and ultrasonic velocity was established. Second, the uncertainty of the testing system was obtained, and the ultrasonic velocities of 192 positions in a 126 kV three-phase basin-type insulator were measured. Finally, the density distribution of the insulator was obtained based on the mapping equation of velocity-density, and a contour plot of density was established by the cubic spline interpolation. The results show that there was a positive linear correlation between the density of standard samples and the ultrasonic velocity, and the determination coefficient was 0.992. Notably, the expanded uncertainty of ultrasonic propagation time for detecting 45 mm-thick EP/Al2O3 composites was only $0.0112~\mu \text{s}$ . The ultrasonic propagation time of detection positions in the insulator was from 31.0634 to $31.4708~\mu \text{s}$ and the difference was greater than $0.0112~\mu \text{s}$ , which illustrated that the testing system meets the requirements for detecting the density of the insulator. According to the contour plot of density, the density distribution of the insulator was shown clearly and efficiently. The density was higher at the bottom edge of the insulator and the upper part of the insert, whereas the density was smaller at the lateral upper part of the insulator and the lower part of the insert. Specifically, the maximum density of the insulator was 2.36 g/cm3 and the minimum density was 2.25 g/cm3. The feasibility of nondestructive testing density by the ultrasonic method is verified, which provides a new method for density evaluation of GIS insulators.

Subsurface Stress Measurement in GIS Epoxy Composite by Using LCR Waves

Internal stress in basin insulators of gas-insulated metal-enclosed switchgear (GIS) can lead to cracks, which affects the safe operation of these apparatuses. In this research, we proposed a subsurface internal stress measurement method for GIS epoxy composites. This method is based on an ultrasonic longitudinal critically refracted (LCR) wave technique. In this study, some epoxy composite specimens were synthesized with similar materials and manufacturing processes to those of 252 kV GIS basin insulators. An ultrasonic stress measurement system that utilized the LCR wave technique was set-up to investigate the relationship between stress and LCR wave propagation time, as well as to measure the compressive stress of the epoxy specimen within 0–50 MPa. The results show that LCR wave propagation time linearly decreased when stress increased in the subsurface zone and the acoustoelastic coefficient was −4.95. We found the relative errors of stress measurements to be less than 13%.

Characteristics of the Partial Discharge in the Development of Conductive Particle-Initiated Flashover of a GIS Insulator

Conductive particles are one of the most important defects which can greatly degrade the performance of gas-insulated metal-enclosed switchgear (GIS). Many efforts have been made to clarify the influence on the withstand voltage, understand the flashover mechanism, and build a comprehensive model to describe the particle-initiated flashover. In this study, a partial discharge (PD) signal detected through a photomultiplier (PMT) and recorded by a high-speed data acquisition (DAQ) system was used to analyze the discharge development of a conductive particle-contaminated GIS insulator under constant high AC voltage. An additional PMT was used as a reference to eliminate the dark count of the PMT and the data collection method of a DAQ system was optimized to capture the pulse waveform of each PD to obtain detailed physical information. Spectra of the PD pulse amplitude over pulse width, PD counts within various amplitude ranges over time and phase resolved partial discharge (PRPD) patterns of the PDs in different stages are obtained through the captured PD waveforms. Characteristics of the PDs from the application of the high AC voltage up to the flashover of the insulator were then analyzed, and it was found that the features of the PDs in the near-flashover stage were significantly different to the previous stages.

An Ultrasonic Longitudinal Through-Transmission Method to Measure the Compressive Internal Stress in Epoxy Composite Specimens of Gas-Insulated Metal-Enclosed Switchgear

Situations of internal stress in basin insulators inside gas-insulated metal-enclosed switchgear (GIS) can lead to cracks, which can influence the safety and stability of apparatus. However, there is currently no research on internal stress measurements for composites of GIS basin insulators, and only measurements for surface stress. In this paper, an internal stress measurement method for GIS epoxy composite is proposed using an ultrasonic longitudinal through-transmission technique based on the acoustoelastic effect. An internal stress measurement system is developed to investigate the relationship between the uniaxial compressive internal stress and the velocity of the ultrasonic wave vertical to the stress in epoxy composite within a range of 0–70 MPa, and to calculate the acoustoelastic coefficient of epoxy composite. The effects of system delay are eliminated in measuring the propagation time. Some epoxy composite cuboid specimens with similar materials and using a manufacturing process similar to those of 252 kV GIS basin insulators are synthesized, and the uniformity of the internal stress in cuboid specimens is verified by finite element simulation. The results reveal a linear increase of the ultrasonic longitudinal wave velocity with increasing stress. It has been shown that the average acoustoelastic coefficient of GIS epoxy composites, using the longitudinal waves vertical to the stress, is 4.556 × 10−5/MPa. Additionally, the absolute errors of the internal stress measurements are less than 12.397 MPa. This research shows that the ultrasonic method based on the acoustoelastic effect for measuring the internal stress in GIS epoxy composites is feasible.

Phase-space joint resolved PD characteristics of defects on insulator surface in GIS

Partial discharges (PDs) initiated by conductive particles attached to the insulator surface in gas-insulated metal-enclosed switchgear (GIS) may occur at different particle tips with varying spatial information. PD modes also differ depending on the spatial position and voltage phase. In this study, PDs were investigated as per phase-space joint resolved characteristics using two photomultiplier tubes and phase-resolved discharge images. PDs were observed to occur mainly at the negative particle tip regardless of the half-cycle. A sudden increase in apparent PD charge is attributed to the corona-creepage transition. The PD mode transition mechanism and effectiveness of the on-site dielectric test for defect detection were also determined. The results presented here may provide theoretical support for GIS defect identification and threat assessment.

An Ultrasonic Pulse-Echo Method to Detect Internal Defects in Epoxy Composite Insulation

Voids or cracks in basin insulators inside a GIS (gas-insulated metal-enclosed switchgear) could trigger partial discharges or surface flashover under electrical stresses, threatening safe GIS operation. For this paper, some epoxy composite specimens were made from similar materials and manufacturing processes to make 252 kV GIS basin insulators. Some voids with different diameters or cracks with different diameters and orientations were artificially made in the specimens with different thicknesses. An ultrasonic pulse-echo system was set up, and ultrasonic tests were carried out on the specimens with voids or cracks. A method to calculate the depth of a defect was proposed by the propagation time of defect reflected waves. The results showed that a depth of 50 mm, a diameter φ of 2 mm void, and a diameter φ of 1 mm crack in epoxy composite insulation were detected by the ultrasonic system using a 1 MHz transducer.

A new method to evaluate the effectiveness of impulse voltage for detecting insulation defects in GIS equipment

Lightning impulse (LI) test is an effective means to detect insulation defects in gas-insulated metal-enclosed switchgear (GIS) equipment. However, the LI test wavefront time Tf will exceed the standard value of 1.2 μs ± 30% for large test load capacitance. Whether extending the Tf will influence defect detection effectiveness should be a concern. In this study, a generating system of impulses with different wavefront parameters was established. The insulation characteristics of a coaxial cylinder structure with an SF6 gas gap with conductive protrusion in a bus under impulses with different wavefront parameters were studied. Experimental results show that the voltage–time curve of the gap shows a bathtub trend that has a flat part in the range of 1 μs to 5 μs. With a Tf increase, the 50% breakdown voltage increases. Whether extending the Tf will influence defect detection effectiveness is analyzed from the standpoint of the different meaning of the breakdown voltage in voltage-time curve and 50% breakdown voltage. The essence of detection effectiveness under impulse voltages with different wavefront parameters is a comparison of the probability of detecting the same insulation defect. Based on the discharge probability distribution, a new quantitative method to evaluate the insulation defect detection effectiveness of impulse voltages for GIS equipment is proposed. The method, based on the 90% discharge voltage value of an insulation defect under a standard LI, normalizes the discharge probability under different wavefront parameters.

Study on waveform parameters of impulse test voltage and on-site docking method for EHV/UHV GIS

GIS (gas-insulated metal-enclosed switchgear) is one of the important components in modern electrical power systems. Compared with traditional open switching devices, GIS has many advantages such as compact structure, smaller occupied area, little influence from environment as well as safe and reliable operation [1–3]. Statistical data show that equipment failure rate of GIS is only 20%–40% of traditional open switching devices. However, as GIS is designed as a fully enclosed structure, once something goes wrong, the diagnosis process is much more complex and the time necessary for fault repair becomes much longer [4–5]. For instance, a severe short circuit fault occurred in Jiangsu Power Grid, China in 2014 due to the development of cracks on a disc insulator. In the same year, abnormal discharges occurred in GIS substations because of a disconnector fault that led to large economic loss and undesired social impacts. Much work had, therefore, been done on analyzing transient events in gas insulated installations in China and internationally [6–9].

Through-Process Finite Element Modeling for Warm Flanging Process of Large-Diameter Aluminum Alloy Shell of Gas Insulated (Metal-Enclosed) Switchgear.

The large diameter metal shell component (LDMSC) is an important part of gas insulated (metal-enclosed) switchgear (GIS). The LDMSC with multi branches is filled with gas under certain pressure. The plastic forming process is an efficient approach to manufacturing the high reliability LDMSC. The warm flanging process has been widely used to form LDMSC using aluminum alloy. The forming process is characterized by local heating, and the distribution of temperature is strongly inhomogeneous. Although the wall thickness of the shell is 10 mm to 20 mm, the ratio of outer diameter to thickness is more than 40. These present some difficulties in the flanging process and result in some forming defects. Detailed forming characteristics are hard to obtain by analytical and experimental methods. Thus, the through-process finite element (FE) modeling considering heating, forming, unloading, and cooling is one of the key problems to research the manufacturing process of LDMSC. In this study, the through-process FE modeling of the warm flanging process of LDMSC using aluminum alloy was carried out based on the FORGE. The thermo-mechanical coupled finite element method was adopted in the modeling, and the deformation of the workpiece and the die stress were considered together in the modeling. A full three-dimensional (3D) geometry was modeled due to inhomogeneous distribution in all directions for the temperature field. The simulation data of local flame heating could be transferred seamlessly to the simulations of the deforming process, the unloading process, and the cooling process in the through-process FE model. The model was validated by comparison with geometric shapes and forming defects obtained from the experiment. The developed FE model could describe the inhomogeneous temperature field along circumferential, radial, and axial directions for the formed branch as well as the deformation characteristic and the unloading behavior during the warm flanging process. By using the FE model, the forming defects during the flanging process and their controlling characteristics were explored, the evolution of the temperature field through the whole process was studied, and deformation and springback characteristics were analyzed. The results of this study provide a basis for investigating deformation mechanisms, optimizing processes, and determining parameters in the warm flanging process of a large-diameter aluminum alloy shell component.

Metal particle movement and distribution characteristics under AC voltage and ball‐plane electrodes

Metal particles, difficult to be eliminated in gas-insulated metal-enclosed switchgear (GIS), can cause GIS discharge and breakdown between electrodes, or flashover on the insulator surface. It influences the development of ultra-high voltage (UHV) projects. Therefore, the work optimised the model of metal particle movement under AC voltage, studying the metal particle movement and distribution characteristics between ball-plane electrodes through experiment and simulation. Under AC voltage, the particle jumps on a small scale on the plane surface. With the increase of voltage, the jump amplitude increases. However, the collision frequency decreases until the particle collides with the ball electrode. When the initial phase angle of power changes, the particle-moving pattern is symmetrical in the angle ranging from 0 to 180°, and from 180 to 360°. The collision frequency changes slightly with the increase of jump amplitude when the angel ranges from 0 to 120°.

Research on the synergy of SF6/N2 mixture gas in low temperature environment

For high latitudes, due to the deficiencies of liquefaction of SF6 and extreme greenhouse effect, gas-insulated metal-enclosed switchgear (GIS), gas-insulated metal-enclosed transmission lines (GIL) and other electrical equipment have begun to use mixed gas of SF6 and N2 as the insulation medium. For this purpose, slightly non-uniform electric field distribution is generated using hemisphere-plane electrodes. Under the excitation of a negative DC high voltage, the breakdown voltage of the SF6/N2 mixture gas is measured at a temperature of 0 to -15°C and a gas pressure of 15 to 60 kPa. The voltage is used to calculate the synergistic coefficient of the mixed gas, and the effect of the temperature and pressure on the synergy of the mixed gas is analyzed. The results show that under slightly non-uniform electric field conditions, the synergy of the mixed gas decreases with decreasing temperature, and increases with increasing gas pressure. It follows that good insulating property of SF6/N2 gas mixture used in a low temperature environment can be achieved by selecting a reasonable temperature and gas pressure.

Study on Influence Factors of Lightning Impulse Test Waveform of UHV GIS Equipment

The lightning impulse withstand voltage test is a test item that must be carried out for type testing, factory test or even field test of electrical equipment such as gas insulated metal-enclosed switchgear (GIS).However, the factors affecting the lightning impulse test waveform are complex and diverse. In this paper, the discharge principle of the impulse voltage generator is studied. Combined with simulation, the influence of different factors on the waveform parameters of lightning impulse test of UHV GIS equipment is obtained. The common methods and improvement measures of waveform debugging are pointed out, and the main factors affecting the parameters of lightning waves are studied.

Effectiveness of on-site dielectric test of GIS equipment

Even for gas-insulated metal-enclosed switchgear (GIS) equipment that has passed an on-site dielectric test, some dielectric failure can occasionally occur without warning. It is necessary to evaluate the effectiveness of on-site dielectric tests of GIS equipment. In this study, two standard test procedures, power-frequency partial discharge (PD) and lighting impulse (LI) withstand test, were carried out in a real model test platform of 550 kV GIS to evaluate the effectiveness of on-site dielectric tests. Through experiments, the minimum detectable defect sizes were determined for different curvature radius values. The results show the limitation of the power-frequency PD test and the need to use of the LI withstand test as supplementary assessment on site. Two calculable constraints of defect detectability were proposed to extend the results to GIS equipment at other voltage levels. The results clarify the cause of dielectric failure without any warning and provide technological guidance for manufacturing and installation.

Effects of electrode chemical reactions on SF6 discharge characteristics in extremely inhomogeneous electric fields

SF6 is widely used in the gas-insulated metal-enclosed switchgear or the corona-stabilized gas spark switch applications as a gas dielectric. It is generally believed that the discharge characteristics are only related to the electric field distribution and gas molecular density; however, the electrode chemical reactions can indeed markedly affect the SF6 discharge characteristics in the extremely inhomogeneous electric fields under the steady-state voltage. In this study, we used a needle-plane electrode system to build an extremely inhomogeneous electric field and examined the discharge characteristics within it including U-p characteristics, corona appearance, and corona current. We also analyzed the micro-region characteristics of the electrode surface, including the surface morphology, elemental composition, and chemical state to fully qualitatively determine the role of the electrode chemical reactions in discharge behavior. We found that the N-shaped U-p curve widens, the filamentous leader channels disappear, and the corona current drops suddenly as the duration of the electrode chemical reactions increases. Varying the surface morphology, elemental composition, and chemical state was observed on the electrodes of different polarities through micro-region analysis. The metal fluoride or metal sulfide film on the electrode surface may serve as a resistive coating due to its low electrical conductivity, which obstructs the leader discharge while enhancing the streamer discharge, suppressing the transition from the streamer to leader discharge and altogether significantly altering the discharge characteristics. The resistive coating produced is the primary cause of the electrode chemical reaction effects on the discharge characteristics, primarily as it depresses the transition from the streamer to leader discharge. The results presented here may provide useful guidelines for further research on SF6 discharge under inhomogeneous electric fields.