Gas Insulated Switchgear Model Research Articles

Investigating the impact of X-ray irradiation on the SF6 gas discharge in GIS equipment

ABSTRACT Gas Insulated Switchgear (GIS) is extensively utilized in power grid systems. However, the existence of numerous photoelectrons in the SF6 gas during X-ray non-destructive testing in ultra-high-voltage (UHV) GIS equipment may induce gas streamer discharge in a strong electric field. To address this issue, in this work, the impact of X-ray irradiation on the SF6 gas discharge in GIS equipment was systematically analyzed. Firstly, one GIS engineering mode with a three-dimensional electric field was established, and a physical GIS model was established by the Geant4 and Garfield++ codes. Secondly, the electrons’ ionization, and multiplication processes in SF6 gas during the X-ray irradiation were studied. Finally, a test platform with an equivalent electric field tube, which had the same intensity as in the GIS equipment, was established to verify the physical GIS model. X-ray beams with 0.1 MeV, 0.16 MeV, 0.3 MeV, and 1.25 MeV energy were used during the test process. From our analysis, it was concluded that X-ray irradiation can cause an electron avalanche in SF6 gas and the intensity of the avalanche is low, which is far away from the appearance of the streamer discharge.

Study on Very Fast Transient Overvoltage Characteristics of Gas-Insulated Switchgear Substation Based on Hybrid Reactive Power Compensation

In recent years, gas-insulated switchgear (GIS) substations have become widely used in power systems. Due to their compact structure, extremely high oscillation frequencies are prone to extremely high oscillation transient overvoltages or very fast transient overvoltages (VFTOs) when the isolating switch or circuit breaker is operated. The characteristics of these special fast transient processes in GIS and the effect of hybrid reactive power compensation (HRPC) on these fast transient processes were studied. A simulation of the GIS model was established, and based on the transient model of HRPC and the theory of the transmission line, the effects of VFTO produced by HRPC switching operation and the parameters of HRPC on VFTO were studied and the differences in the characteristics of VFTOs in substations with or without HRPC. Based on the conclusions of our study on the influence of HRPC on VFTO, the inhibitory effects of a ferrite magnet ring and an inhibitor busbar on VFTO were verified.

Three-Dimensional FDTD-Based Simulation of Induced Surges in Secondary Circuits Owing to Primary-Circuit Surges in Substations

Currently, plenty of sensitive electronic devices are installed in secondary circuits in substations and power plants. Electronic devices may malfunction and become damaged owing to electromagnetic disturbances caused mainly by lightning surges. To protect electronic devices properly, it is useful to predict electromagnetic transient phenomena and evaluate the effectiveness of lightning protection methodologies. Recently, the finite-difference time-domain (FDTD) method, which is one of the full-wave numerical approaches, has become a very powerful tool for analyzing electromagnetic transient phenomena in 3-D structures and grounding systems. In this article, first, we study the modeling of protection relay units and instrument transformers for FDTD-based surge simulations. Second, using an FDTD-based electromagnetic transient simulation code, we model a test platform of a gas-insulated switchgear (GIS), instrument transformers, and a control cable above a grounding grid. By applying a surge voltage to the center conductor of the GIS model, we calculate the transient voltage in the GIS model, the transient response of the grounding grid, and the induced voltage on the control cable, and compare the calculated results with measured waveforms for validation.

Detection and Diagnosis of Defect in GIS Based on X-ray Digital Imaging Technology

For better application of X-ray digital imaging technology in defect detection in Gas Insulated Switchgear (GIS), it is essential to investigate the typical defect and establish the defect database, which has not been adequately performed in previous work. Systematic experimental research is also needed to accumulate data and experience. In this research, an experimental platform, including Computed Radiography (CR) imaging system and a GIS model, is built, and extensive tests of different kinds of typical defects are studied. The influence X-ray irradiation on SF6 under different tube voltage levels is firstly examined, which proves that the withstand voltage of SF6 gas has not been affected and no dissociation has been found. Then, several kinds of defects are tested by X-ray digital imaging technology. The successful application examples of “visual” detection of defects further prove the practicability and validity of the X-ray digital imaging technique. Finally, the image database of typical defects inside of GIS is established and the defect risk is also analyzed in three levels, which would be useful for the defect severity diagnosis and risk assessment.

Time–frequency analysis of PD‐induced UHF signal in GIS and feature extraction using invariant moments

The ultra-high-frequency (UHF) method is efficient in partial discharges (PDs) detection in gas-insulated switchgear (GIS). The features extraction of UHF signals is significant for propagation characteristics analysis and PD pattern classification. The PD-induced UHF signals are acquired by the internal UHF sensors in an actual 252 kV L-shaped GIS. The short-time Fourier transform method is applied to process UHF signals and describe the propagation characteristics in L-shaped GIS. Hu's invariant moments of energy density distribution are extracted as features in time-frequency plane. The features are utilised to discriminate different PD defect patterns in actual GIS model by the support vector machine classifier and achieve good results. Finally, a novel system of features extraction and classification of UHF signals is summarised.

Full-Maxwell Simulations of Very Fast Transients in GIS: Case Study to Compare 3-D and 2-D-Axisymmetric Models of 1100 kV Test Setup

Development and type testing of gas-insulated switchgear (GIS) disconnectors are supported with the simulation-based analyses of very fast transients (VFTs) that are associated with the disconnector switching operations. In order to analyze local field values in the entire GIS geometry, the full-Maxwell approach needs to be involved for simulating the VFT generation process. According to power substation layout studies, 90 ${}^{\circ }$ -angled GIS disconnectors are often used in GIS projects, since they offer most layout options and, at the same time, require the lowest number of GIS components. This implies that the test setups are asymmetric, thus the direct use of the full-Maxwell approach requires 3-D models, the application of which is considered to be highly demanding from a numerical point of view. The paper shows a comparison of the results obtained from full-Maxwell numerical simulations for a development test setup of 1100 kV GIS. The analyses are conducted for full 3-D geometry and for the corresponding 2-D-axisymmetric geometry. Example simulations of the VFT overvoltage (VFTO) waveforms are presented for both geometries, together with a comparison of the numerical effort needed for solving the associated field equations. The presented approach based on the 2-D-axisymmetric GIS model allows one to significantly reduce the numerical effort involved to support design work and development tests.

Partial Discharge Pattern of Various Defects Measured by Spiral Antenna as UHF External Sensor on 66 kV GIS Model

This paper deals with partial discharge (PD) measurement in gas insulated switchgear (GIS) using spiral antenna as UHF external sensor. PD detection in UHF band is effective because it detects electromagnetic (EM) wave induced by PD with high S/N ratio. External sensor was used to detect leaked EM wave signals from insulation spacer of GIS tank. The experiment was conducted in 66 kV GIS model with metal type spacer. There is insulation window in the spacer. PD was generated by some artificial defects in GIS and an external PD source. The leaked EM wave propagated through spacer aperture was measured using spiral type sensor without filter and amplifier. The peak to peak value (Vpp) and the transmission rate of electromagnetic wave signals were evaluated. The PD patterns were observed. The results showed that the PD was detected by the spiral antenna. PD pattern was unique for each defect. These results are considered to be useful for enhancement of database PD diagnosis.

Recognition of GIS Insulating Defect Types Based on Ultrasonic Detection

In this paper, high voltage conductor metal protrusions, suspended particles and immobilized metal particles on gas insulated switchgear (GIS) insulators were simulated in the GIS model. The high voltage conductor metal protrusions defect was simulated by a needle-plate model. The GIS model was filled with 0.4MPa SF6 gas. When the voltage was added to 60kV, the three models all had stable discharge. Ultrasonic sensor was used to measure the discharge waveform for 100 groups. The absolute value of difference between the amplitude of adjacent half wave as Udif and the absolute sum of a cycle of the signal as Utal were chosen as the characteristic parameters. The defect types were recognized with BP neural network and the recognition rate is about 80%.

Analysis of Distribution, Pattern, and Vector of Electric Field in the Inter Phases Region of Three-phase Gas Insulated Switchgear

This paper deals with the electric field characteristics in the inter-phases region of three-phase gas insulated switchgear (GIS). The electric field in a three-phase construction of a simplified GIS model was analyzed. The results show that in the inter- phases region the direction and the magnitude of electric field vector varies with the location of the observation point while in the phase-enclosure region the direction of the electric field vector tends to linear and constant. There is no zero electric field on the particle tip of a particle in the inter-phases region, except S90 particle. There is zero electric field on the particle tip of a particle in the phase-enclosure region every half cycle of applied voltage. The maximum electric field of the particles on the inter-phases region generally is higher than one of the particles on the phase-enclosure region. The electric field vector locus in the inter-phases region varies: linear, elliptic, or circular while one in phase-enclosure region is constant and linear.

Propagation properties of PD-induced electromagnetic wave in 66 kV GIS model tank with L branch structure

The authors investigated the effects of a corner that affects the transmission characteristics of a partial discharge (PD) induced electromagnetic (EM) wave, using a gas insulated switchgear (GIS) model with an L-shaped branch. The authors also experimentally investigated the change of amplitude of PD-induced EM wave around the passage of the Lshaped part using a disc-type ultra-high frequency (UHF) sensor located in a 66 kV model GIS. In addition, the effects of transverse electric (TE) mode were examined using a low pass filtering process, and a finite difference time domain (FD-TD) simulation with a simple model was performed. Subsequently, the effects of the L-shaped part that affected the EM wave transmission characteristic were discussed based on a comparison of the results with the analysis. It was found that the effects of the L-shaped part that affected the transmission characteristics of the PD-induced the EM wave did not affect the transverse electromagnetic (TEM) wave mode component, and reflection was generated with a higher frequency component above TE11 mode. It was also shown that the amplitude of the propagating EM wave changed significantly around the L-shaped part due to the superimposition of the reflected TE mode on the latter part of the incoming EM wave.

Examination of Single-phase Partial Discharge Monitoring Device for Partial Discharge Diagnosis on Three-phase GIS

This paper deals with partial discharge induced electromagnetic wave investigation on three-phase GIS using UHF method and the application of single-phase partial discharge monitoring device (PDM) on three-phase gas insulated switchgear (GIS). The PD source is a protrusion at different positions on the conductor or on the tank. Frequency and phase spectrums of EMW signals emitted by PD at different positions were observed. The most dominant frequency of EMW signal in three-phase GIS was estimated from the cutoff frequency (fc) formula for single-phase GIS. The main difference in frequency spectrum between three-phase and single-phase GIS was found to be the shift of fc to the lower value for three-phase GIS. The presence of three conductors can be considered as increase in an equivalent radius of three-phase conductor by a factor of 1.6 for this GIS model. The phase of PD phase pattern in the phase spectrum depended on the particle position. The PD sources on three-phase GIS were diagnosed by single-phase PDM device. The success rate of diagnosis results is low. The error is predicted to be caused by error in phase recognition of PD pattern. The change in phase shift setting of PD phase pattern in PDM device based on the phase angle of applied voltage at maximum electric field gave better diagnosis results. Index Terms: three-phase, GIS, PDM device, phase shift setting, success rate

The Insulation Evaluation of N2:O2Mixture Gas

With the improvement of industrial society, high quality electrical energy, simplification of operation and maintenance, and ensuring reliability are being required. Also we request an urgent change from SF? gas to an environment-friendly gas insulation material. In this paper, the experiments of breakdown characteristics by pressure and gap change of N₂/O₂ mixture gas through a GIS (Gas Insulated Switchgear) model were described. This paper reviews basic data of the surface discharge characteristics for Teflon resin in not only pure N2, N₂:O₂ mixture gas as being focused on environmentally-friendly insulating gas, but also SF?. Also, insulation characteristics by breakdown voltage and surface discharge voltage of N₂:O₂ mixture gas in the experimental chamber were studied.

Blind Source Separation of Mixed PD Signals Produced by Multiple Insulation Defects in GIS

Partial discharge (PD) source signals concurring at different internal positions in gas insulated switchgear (GIS) may be mixed linearly or nonlinearly when they are propagating through GIS pipes. To identify the interior insulation defects in GIS, it is important and intricate to extract these individual PD source signals from the mixed PD signals. This paper applies the blind source separation (BSS) theory to acquire individual source signals assisted by complex wavelet transform. First, a maximizing signal-to-noise ratio (MSNR) BSS algorithm is introduced. Then simulated PD mixed signals are constructed from four individual ultra-high frequency theoretical PD signals and employed to implement BSS separation. Finally, two typical individual PD signals sampled from GIS model are adopted for testing. Both can produce satisfying result, which shows that it is feasible to apply BSS to separate the mixed PD signals in GIS.

Propagation Characteristics of Higher-order Mode Electromagnetic Signals in Coaxial GIS Model with Various Conditions of Arch-shaped UHF Sensor

Partial discharge detection using a UHF band signal is a well known advanced insulation diagnosis method in gas insulated switchgear (GIS), and has been well studied. In contrast to conventional diagnosis with lower frequencies in the kHz range, UHF band signal above the cutoff frequency has been detected with higher-order modes that only appear in electromagnetic signal propagating inside the GIS tank. This is because the wavelength of UHF band signals is comparable to the GIS tank size. The authors had observed the characteristics of such higher-order electromagnetic waves with a focus on the resonance characteristics of the TE11 mode, using a disk-shaped UHF sensor with the sensor extending into the inside of the tank. The purpose of this paper is to investigate the propagation characteristics of higher-order mode waves in a coaxial GIS model. Considering application to actual equipment, it was investigated that the output of a sensor with an arch-shape not extending into the inside of the tank, which has less influence on the propagation mode of the inner electromagnetic wave. In the frequency domain below the cutoff frequency of the TE11 mode, the output characteristics were almost independent of the installation position of the UHF sensor, but in the higher frequency domain the output power displayed discontinuous increases at some frequencies. It was also studied that the circumferential dependence of sensor output. For higher-order modes resonant characteristics appeared that depended on the tank length, and it was recognized that the electric field distribution inside the tank influenced the output of the UHF sensor at resonant frequencies. Further, it was found that installing a spacer inside the tank shifted resonant frequencies and the influence of the spacer consistent with the relationship between the spacer position and the electric field distribution inside the tank.

Examination of Electromagnetic Mode Propagation Characteristics in Straight and L-Section GIS Model Using FD-TD Analysis

It is an effective method of insulation accident prevention for gas-insulated switchgear (GIS) to detect a partial discharge (PD) that occurs as a preceding phenomenon for an insulation accident. Among various methods, a PD detection method based on the detection of electromagnetic emission through measurement of the UHF band (300 MHz to 3 GHz), which is relatively free of influences from external noises, is drawing attention as an effective method in terms of extensive and highly sensitive detection. This paper describes conducting EM-wave propagation analysis on GISs with L-sections using the finite difference-time domain (FD-TD) method and examining the influences of the Insertions on the propagation characteristics of EM-wave modes with comparison of straight GIS part. As a result, this study identified that, even on a straight GIS, the velocity dispersion characteristic of high-order modes resulted in a decrease in the crest value even if there is no reflection or conductor loss in the discontinuities. And that mode conversions and reflections in L-sections also resulted in a decrease in the crest value.

Electromagnetic Wave Propagation in a Coaxial Pipe GIS Model

Partial discharge (PD) detection using a UHF band signal is a well known advanced insulation diagnosis method in a gas insulated switchgear (GIS) and has been actively studied. Detailed investigation of detection principles and electromagnetic wave propagation inside the GIS tank is required for significant improvement in sensitivity and accuracy. As the wavelength of UHF-band signals is comparable to the GIS tank size, higher-order modes also appear in electromagnetic waves propagating inside at frequencies at or above a certain value, creating complicating phenomena. This study investigated these phenomena, focusing on experiments with a UHF sensor inside a coaxial pipe as a simplified model of GIS structure, while varying conditions such as sensor shape and installation position (both circumferential and longitudinal), the input method of a simulated PD signal, and the presence or absence of an insulating spacer. On the low frequency side (TEM mode only), the sensor output can be described by an equivalent electric circuit determined by the coupling capacitance between the sensor surface, the center conductor and the tank. At the cutoff frequency of the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> mode or above, resonance phenomena appeared, which were related to the pipe length. Further, it was found that installing an insulating spacer inside the coaxial pipe shifted the resonant frequency in a manner closely connected with the spacer position's relationship to the electric field distribution inside the tank.

Preventive maintenance system with a different gas injecting facility for GIS

A preventive maintenance system for gas insulated switchgear (GIS) is developed. It detects signs of trouble and prevents breakdowns in service. The system constantly monitors UHF signals, which are generated by partial discharges (PDs), and propagate in the GIS, by using couplers built into the apparatus. The PDs are detected at high sensitivity (5 pC) and located according to the attenuation of the signals. Then the system injects a different gas into the section where PDs are occurring and improves the dielectric strength. This prevents faults in service and allows remedial actions to be taken with less accuracy. By injecting a small quantity (5-10%) of c-C/sub 4/F/sub 8/ into the GIS, dielectric strength is raised more than 20%. A preventive maintenance system with a facility to inject a different gas is constructed for a full-scale GIS model. The system detects and locates PDs, and automatically injects the different gas to improve the dielectric strength. >